TWI793080B - Continuous-wave organic thin-film distributed feedback laser and electrically driven organic semiconductor laser diode - Google Patents

Abstract

Disclosed are a current excitation type organic semiconductor laser containing a pair of electrodes, an organic laser active layer and an optical resonator structure between the pair of electrodes and a laser having an organic layer on a distributed feedback grating structure. The lasers include a continuous-wave laser, a quasi-continuous-wave laser and an electrically driven semiconductor laser diode.

Description

Continuous Wave Organic Thin Film Distributed Feedback Laser and Electrically Driven Organic Semiconductor Laser Diode

The invention relates to a continuous wave organic thin film distributed feedback laser and an electrically driven organic semiconductor laser diode.

The present application discloses the following inventions: 1. A current-excited organic semiconductor laser, which includes two electrodes, an organic optical gain layer and an optical resonator structure. In the specification, a current-excited organic semiconductor laser may be referred to as a current-injected organic semiconductor laser or an electrically driven organic semiconductor laser. 2. Laser according to item 1, wherein the organic optical gain layer consists of at least one charge transport layer and at least one light amplification layer resulting from stimulated emission. 3. The laser according to item 1 or 2, wherein at least one of the two electrodes is transparent. 4. The laser according to any one of items 1 to 3, wherein the optical resonator structure consists of a distributed feedback (DFB) structure. 5. The laser according to any one of items 1 to 4, wherein the optical resonator structure is a one-dimensional resonator structure. 6. The laser according to item 5, wherein the optical resonator structure consists of a second order Bragg scattering region surrounded by a first order Bragg scattering region. 7. The laser according to any one of items 1 to 4, wherein the optical resonator structure is a two-dimensional resonator structure. 8. The laser as in item 7, wherein the optical resonator structure is a circular resonator structure. 9. The laser according to any one of items 1 to 3, 7 and 8, wherein the optical resonator structure consists of a distributed Bragg reflector (DBR) structure. 10. The laser according to any one of items 1 to 9, which contains at least one hole transport or injection region and at least one electron transport or injection region. The hole transport region may be present in the organic optical gain layer or may be a layer formed on the organic optical gain layer. This layer may be free of organic gain media and may consist only of dopants. Regions present in the organic optical gain layer may contain dopants and organic gain media. The hole transport region in the organic optical gain layer can be formed by doping the organic optical gain layer with a dopant. Doping can be performed by doping a dopant from one surface of the organic optical gain layer. The electron transport region may exist in the organic optical gain layer or may be a layer formed on the organic optical gain layer. This layer may be free of organic gain media and may consist only of dopants. Regions present in the organic optical gain layer may contain dopants and organic gain media. The electron transport region in the organic optical gain layer can be formed by doping a dopant in the organic optical gain layer. Doping can be performed by doping a dopant from one surface of the organic optical gain layer. 11. The laser according to item 10, wherein the hole transport or injection region contains acceptors. 12. The laser according to item 10, wherein the hole transport or injection region is doped with acceptors. 13. The laser according to any one of items 10 to 12, wherein the acceptor is a metal oxide. The metal oxide may be MoO ₃ . 14. The laser according to any one of items 10 to 13, further comprising an accepting layer between the hole transport or injection region and the anode. The anode is one of the two electrodes. 15. The laser according to any one of items 10 to 14, wherein the electron transport or injection region contains a donor. The donor may be an alkali metal such as Cs. 16. The laser according to item 15, wherein the electron transport or injection region is doped with a donor. 17. The laser according to any one of items 10 to 16, further comprising a donor layer between the electron transport or injection region and the cathode. The cathode is one of the two electrodes. 18. The laser according to any one of items 1 to 17, which has no organic layer other than an organic optical gain layer. 19. The laser according to any one of items 1 to 18, wherein the optical resonator structure is an external optical resonator structure. 20. The laser according to any one of clauses 1 to 18, wherein the optical resonator structure is located between two electrodes. 21. The laser of any one of items 1 to 20, further comprising a current confinement structure between the two electrodes. 22. The laser according to any one of items 1 to 21, wherein the optical resonator structure is a whispering high-sounding gallery type optical resonator structure. 23. The laser according to any one of clauses 1 to 22, wherein the excitons are generated by electric current excitation and overlap the optical resonance mode of the optical resonator structure. 24. The laser of any one of items 1 to 23, which does not exhibit substantial exciton destruction at the wavelength of the laser. The loss caused by exciton mutual destruction is preferably lower than 10%, more preferably lower than 5%, further preferably lower than 1%, further preferably lower than 0.1%, further preferably lower than 0.01%, the best is 0%. 25. A laser as in item 24 which does not exhibit substantial singlet-singlet and triplet-triplet mutual destruction. 26. The laser of any one of items 1 to 25, which exhibits no substantial polaron absorption loss at the laser wavelength. There is no substantial overlap between polaron absorption and emission spectra of organic semiconductor lasers. The loss due to polaron absorption is preferably less than 10%, more preferably less than 5%, even more preferably less than 1%, still more preferably less than 0.1%, still more preferably less than 0.01%, the best is 0%. 27. The laser according to any one of items 1 to 26, wherein the ratio of electron mobility to hole mobility in the organic optical gain layer is in the range of 1/10 to 10/1. The ratio is preferably from 1/5 to 5/1, more preferably from 1/3 to 3/1, still more preferably from 1/2 to 2/1. 28. A laser having an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium. 29. The laser of item 28, wherein the DFB grating structure is a mixed-order DFB grating structure in which a second-order Bragg scattering region is surrounded by a first-order scattering region. 30. The laser according to item 28, wherein the DFB grating structure is a mixed-order DFB grating structure in which second-order Bragg scattering regions and first-order scattering regions are formed. 31. The laser as in item 28, wherein second-order Bragg scattering regions and first-order scattering regions are alternately formed. 32. The laser according to any one of items 28 to 31, wherein the DFB grating structure has a circular structure. 33. The laser of any one of items 28 to 32, wherein there is no substantial spectral overlap between excited state absorption and laser emission. 34. The laser of any one of items 28 to 33, wherein the stimulated emission cross section σ _em is 100 times or more than the triplet excited state cross section σ _TT , preferably 400 times or more, more Jiadi is 700 times or more than 700 times larger. 35. The laser according to any one of items 28 to 34, wherein the organic layer contains a host material and at least one dopant. 36. The laser according to any one of items 28 to 35, wherein the organic layer is directly or indirectly covered with sapphire. 37. The laser according to any one of items 28 to 36, wherein the organic layer is covered directly or indirectly with a fluoropolymer. 38. The laser according to item 37, wherein the thickness of the fluoropolymer is less than 3 μm. 39. The laser according to item 38, wherein the organic layer covered with fluoropolymer is further covered with sapphire. 40. The laser of any one of items 29 to 39, which is a continuous wave laser. 41. The laser of any one of items 29 to 39, which is a quasi-continuous wave laser. 42. The laser according to any one of items 1 to 41, wherein the organic layer contains an organic compound having at least one stilbene unit. 43. The laser according to any one of items 1 to 41, wherein the organic layer contains 4,4'-bis[( N - carbazole)styryl]biphenyl (BSBCz). 44. The laser as in item 43, wherein the organic layer contains 4,4'-bis[( N - carbazole)styryl]biphenyl (BSBCz) and 4,4'-bis( N - carbazolyl)- 1,1'-biphenyl (CBP). 45. The laser according to any one of items 1 to 41, wherein the organic layer contains a compound having at least one fennel unit. A compound having a fennel unit may be a compound having at least two fennel structures, such as heptaben, octacyl and bistila core dendrimers. 46. The laser according to any one of items 1 to 45, wherein the thickness of the organic layer is 80 to 350 nm, preferably 100 to 300 nm, more preferably 150 to 250 nm. 47. The laser according to any one of items 1 to 46, wherein the depth of the grating structure is below 75 nm, preferably 20 to 70 nm. 48. The laser according to any one of items 1 to 47, wherein the grating structure is made of _SiO2 . 49. The laser of any one of items 1 to 48, which does not contain a triplet quencher.

(1) 其中m 為繞射角，l _Bragg 為腔中之共振波長，n_eff 為均一波導之有效折射率，且L為光柵週期。在二階光柵(m =2)的情況下，一階繞射光自薄膜之表面垂直提取，而共平面回饋由2階繞射提供。根據耦合模式理論，不允許滿足布拉格條件(1)之波長在薄膜[15]中傳播。此係由於折射率之週期性調變，其導致集中於布拉格波長上之光子阻帶的出現。從而，在l _Bragg 下，觀測到發射中之突降且雷射振盪出現於位於阻帶邊緣上之一對波長上。在二階光柵中，雷射振盪僅處於阻帶(處於最高波長下)之一個邊緣處。在此波長下，由於較低輻射損失，臨限值較低[16]。 共振腔經由兩個參數對雷射效能產生影響：限制因數G 及品質因數Q 。雷射臨限值處之激子密度與G 及Q 兩者成反比[17]。因此，DFB共振腔之幾何結構之最佳化對減小損失至關重要，該損失可藉由G 及Q 定量。 此工作之目標在於研究有機薄膜厚度對雷射效能(包括能量臨限值及雷射波長)的影響。首先，雷射之設計為固定的。為了推斷獲得ASE波長下之雷射所需之光柵週期，藉由計算波導結構之有效折射率來完成此步驟。有機薄膜之厚度自100 nm變為300 nm之，且計算在各厚度下的有效折射率。其次，為了獲得對雷射臨限能量隨著厚度之變化的物理性瞭解，執行光學模擬。根據薄膜厚度計算共振腔之品質因數及限制因數且與有機雷射裝置之實驗能量臨限值進行比較。2 . 裝置結構及模擬細節 構成此工作中研究之二階DFB有機雷射之光柵耦合波導之幾何結構描繪於圖33中。波導結構由增益介質(6%wt BSBCz：CBP)組成，該增益介質由藉由較低折射率的SiO₂ 光柵及空氣包圍之高折射率層構成。增益介質由真空沈積於2階DFB光柵上之6wt% BSBCz：CBP摻合物薄膜組成。藉由電子束微影將光柵製作於SiO₂ 基板上。在別處描述DFB雷射之製造[4]。 用於模擬之輸入參數為層之厚度及折射率。認為空氣(n_a =1)及SiO₂ 基板(n_s =1.46)係半無限層。認為6wt% BSBCz：CBP摻合物之折射率n_f 等於[18]中所報導之CBP之折射率(n_f 約1.8)。有機薄膜之厚度自100 nm變為300 nm。雷射之結構經設計使得雷射在BSB-Cz之經放大自發發射(ASE)波長(約477 nm)下振盪[19]、[20]。模擬軟體 ： 使用自製python 3.5軟體指令碼執行有效折射率計算及法諾擬合 使用Comsol 5.2a軟體之RF模組中之有限元方法自共振腔模式之本徵值之計算提取品質因數及限制因數。3. 結果及論述 3.1 波導特性化 ( 有效折射率計算 ) 為了使用布拉格條件(方程式1)計算光柵週期，需要均一波導(無光柵)之有效折射率n_eff 。在此模型中，忽略光柵，因此波導厚度為有機薄膜之厚度。藉由根據有機薄膜厚度在波長477 nm下求解傳播波方程式[21]計算有效折射率n_eff 的值。 在此計算中，吾人認為不對稱波導不具有光柵(圖34(a))。在不對稱3層厚塊波導之情況下，各區域中之電場由以下給出：

其中：

其中k₀ 為真空傳播常數模式

，且β 為引導模式之傳播常數

。自應用以下邊界條件之後獲得的超越方程式計算波導模式之有效折射率：

圖34(b)呈現自方程式6及方程式7導出的波導色散曲線，其展示在雷射波長477 nm下有效折射率隨有機薄膜厚度之變化。根據此等曲線，吾人可推斷在給定厚度下之傳播模式的數目及特定傳播模式之截止厚度。在此工作中，厚度經選擇以自100 nm變為300 nm。對於低於280 nm之厚度，僅允許基諧模TE₀ 振盪。厚度增加至高於280 nm導致高階(TE₁ ，TE₂ )存在。 一旦計算出有效折射率，吾人可在不同薄膜厚度下使用布拉格條件(方程式1) 推斷光柵週期在l_ASE =477 nm時之值。對於200 nm薄膜厚度，n_eff =1.7。滿足布拉格條件(方程式1)之光柵週期L之值為280 nm。在下文中，吾人將光柵週期固定在280 nm且將光柵深度固定在70 nm厚度。有機薄膜之厚度僅自100 nm變為300 nm。3.2 DFB 共振腔最佳化 藉由共振腔之光子壽命及限制因數描述共振腔。光子壽命t表示光子在腔中花費的時間(該腔中的光子損失的速率)。光子可藉由逃出腔或藉由經材料吸收而損失。此光子壽命t如下與腔之品質因數Q有關：

其中w₀ 為共振角頻率。 以兩種不同方法計算光學腔之Q因數。(1) 本徵模式計算 在第一方法中，使用Comsol軟體之RF模組中之有限元方法自共振腔模式之本徵值之計算提取品質因數。計算域限於光柵之一個週期單位單元。弗羅奎(Floquet)週期邊界條件應用於橫向邊界，且散射邊界條件用於頂部域及底部域[22]，[23]。固有頻率求解器用於尋找共振腔之傳播本徵模式。根據本徵值之實數部分及虛數部分，導出Q因數：

其中α 為阻尼衰變

。此外，使用以下表達式計算本徵模式之限制因數：

其中E_norm 為本徵模式之歸一化電場強度分佈。(2) 反射光譜之法諾擬合 用於提取品質因數之第二方法由使用以用於正入射TE偏振平面波(其電場平行於光柵)之Comsol軟體實施之散射矩陣計算反射光譜構成[ref]。隨後，藉由將模擬反射光譜中存在之共振線寬與以下法諾共振方程式擬合獲得Q因數(方程式8) [24]：

其中w ₀ 為中心頻率，t 為共振之壽命，r 及t 為具有與光柵相同的厚度及有效折射率n_eff,g 之均一厚塊之振幅反射及透射係數。在二元光柵之情況下，可使用以下有效介質理論描述有效折射率[25]：

其中ff 經定義為光柵寬度w 與週期L之比。 圖35展示根據波長及薄膜厚度而計算的反射光譜及使用方程式11之對應的擬合法諾共振曲線。對於具有100、150、200、250及300 nm之薄膜厚度之腔，分別觀測到在448、462、472、478及483 nm之波長處的反射波峰。在此等波長處，由於藉由光柵及漏光波導模式繞射的波之間的相位匹配而發生共振[26]、[27]。因此，多個反射在波導中發生且入射光之波長由波導光柵之共振選擇。 如由章節3.1中所呈現之計算及由先前報導之工作所確認[28]，d_f 之增加使得模態n_eff 增加(圖34(b))，其引起雷射波長之調諧。如吾人於圖36(a)中可見，d_f 之增加引起雷射發射之光譜紅移。實驗雷射波長與自法諾模型及章節3.1中指示「模型d_f +h_g 」之模型的經計算雷射波長的比較呈現於圖36(b)中，其中h_g 係指光柵之深度。兩種模型提供大致相同的結果，接近實驗值，但在較小d_f (＜200 nm)下實驗波長與計算波長之間的間隙仍然顯著(Δλ＞10 nm)。據報導，當比率h_g /d_f 超出0.3時[28]，在d_f 約200 nm及低於200 nm的情況下指數耦合為支配機制。當指數耦合比增益耦合更具支配性時，雷射不會在如上文所提及之λ_Bragg 附近出現。因此，實驗雷射波長與經計算雷射波長之間的偏差可藉由針對低於200 nm之d_f 之指數耦合之支配性來解釋。 圖37(a)展示經計算之Q 因數及Γ 值。用於計算Q 因數之兩種方法均得出相同結果。可見，Γ 隨著d_f 增加，展示良好光學限制。此係歸因於基諧模TE₀ 之n_eff 之增加。然而，共振腔之Q 因數在200 nm之d_f 值下變得最高。不同d_f 之經量測能量臨限值E_th 呈現於圖37(a)中。吾人可觀測到Q 因數與E_th 成反比。此外，當d_f 自100 nm增加至200 nm時，E_th 減小。此係歸因於Q 因數及Γ 兩者之增加。在200 nm之d_f 值下，E_th 展示最小值，且接著隨d_f 增加。較大d_f 之較高E_th 係歸因於共振腔之較低Q 因數。 最後，將自計算及法諾擬合提取之峰值反射之半高全寬(FWHM)與實驗雷射發射之FWHM進行比較[圖37(b)]。實驗FWHM值及經計算FWHM值兩者展示與針對等於200 nm之d_f 獲得的最小值相同的趨勢。3.3 利用囊封之 DFB 雷射最佳化 在此章節中，使用CYTOP計算經囊封DFB雷射之G 及Q 因數。用於光學模擬之輸入參數為有機薄膜厚度及層之折射率。認為CYTOP (n _CYTOP =1.35)及SiO₂ 基板(n _SiO2 =1.46)係半無限層。認為6wt% BSBCz：CBP薄膜之折射率n_f 等於所報導之CBP之折射率(n_f =1.85) (1 )。BSBCz：CBP薄膜之厚度d₀ 自100 nm變為300 nm。由於頂部表面結構化，在厚度(h_g -h_{g ( 頂部 )} )/2=30 nm之薄層上添加具有深度h_{g ( 頂部 )} =5 nm之薄光柵。3.3.1 薄膜厚度變化 首先，吾人在藉由計算G 及Q 因數來使光柵深度h _g 保持恆定(h _g =65 nm)的同時研究薄膜厚度d₀ 之變化之效應。表S1展示計算結果。表 S1 . 薄膜厚度、共振波長、品質因數及限制因數。

當厚度增加時，G 及Q 因數增加，但由於共振波長λ ₀ 自增益材料之ASE波長的移位，200 nm之d₀ 保持用於裝置操作之最佳厚度。3.3.2 光柵深度變化 其次，吾人在藉由計算G 及Q 因數使d₀ 保持恆定(d =200 nm)的同時研究h _g 變化之效應。下表S2展示計算結果。表 S2 . 光柵深度、共振波長、品質因數及限制因數。

藉由減小光柵深度，Q 因數增加而G 仍然幾乎相同。然而，淺光柵之製造具有挑戰性，因為深度之較小變化將極大地影響光柵之光學回應。雖然在將來工作中必定可改良此態樣，但在此研究中選擇65 nm深度似乎為最適當的。3.3.3 經囊封及未經囊封裝置之間的比較 使用相同幾何結構完成計算在經囊封的情況下，頂部層為具有1.35之折射率之CYTOP。在未經囊封的情況下，CYTOP由空氣替換(n =1)。在此情況下，Q 因數及G 增加且共振波長略微藍移，如表S3中所展示。表 S3 . 經囊封裝置與未經囊封裝置之間的共振波長、品質因數及限制因數的比較。

然而，基於實驗結果，經囊封之裝置展示出比未經囊封之裝置更好的效能(FWHM)。此可歸因於當吾人囊封裝置時頂部表面之變化或歸因於免於濕氣影響的保護。3.3.4 2 階光柵區域之尺寸之影響 使用2階區域之不同尺寸以實驗方式判定BSBCz：CBP (6:94wt.%)摻合物混合階DFB雷射之雷射臨限值。結果顯示於圖17中。可見，用於此研究之DFB架構(其對應於等於36之週期之數目)並未完全最佳化，表明藉由僅在共振器結構上播放而使裝置效能之進一步改良應為可能的。參考文獻 1. C. Ge, M. Lu, X. Jian, Y. Tan, and B. T. Cunningham, “Large-area organic distributed feedback laser fabricated by nanoreplica molding and horizontal dipping,” vol. 18, no. 12, pp. 12980-12991, 2010. 2. H. Nakanotani, S. Akiyama, D. Ohnishi, M. Moriwake, M. Yahiro, T. Yoshihara, S. Tobita, and C. Adachi, “Extremely low-threshold amplified spontaneous emission of 9,9-disubstituted-spirobifluorene derivatives and electroluminescence from field-effect transistor structure,”Adv. Funct. Mater. , vol. 17, no. 14, pp. 2328-2335, 2007. 3. G. Tsiminis, Y. Wang, P. E. Shaw, A. L. Kanibolotsky, I. F. Perepichka, M. D. Dawson, P. J. Skabara, G. A. Turnbull, and I. D. W. 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Vol.112,no.4, pp. 43104, 2012.章節 B . 混合階 DFB 裝置之雷射屬性 在20 Hz之重複率下及337 nm之波長下遞送800 ps脈衝之氮雷射之脈衝式光學泵浦下，檢查到使用BSBCz純薄膜或BSBCz:CBP (6:94 wt.%)摻合薄膜作為增益介質之經囊封之混合階DFB裝置之雷射屬性。在CBP摻合薄膜之情況下，激勵光主要由CBP主體吸收。然而，CBP發射與BSBCz吸收之間的較大光譜重疊保證自主體分子至客體分子之高效的Förster型能量傳遞(2 -6 )。藉由在337 nm光激勵下之CBP發射之缺失來確認此情況。圖19A至圖19E顯示在低於及高於臨限值之不同激勵強度下垂直於BSBCz薄膜及BSBCz:CBP (6:94 wt.%)薄膜之表面所收集的發射光譜。在低激勵強度下，對於純薄膜及摻合薄膜分別在480 nm及483 nm處觀測到對應於DFB光柵(2 )之光阻帶的布拉格突降。布拉格突降位置中之微小變化大概歸因於摻合薄膜及純薄膜之略微不同的折射率(2 -6 )。隨著泵浦強度增加高於臨界臨限值，在純裝置及摻合裝置兩者中出現窄發射峰，指示雷射之開始。亦可看出，雷射峰之強度增加比光致發光背景快，提供與經刺激發射相關聯之非線性之證據。發現雷射波長對於摻合薄膜為484 nm且對於純薄膜為481 nm。圖19C至圖19D展示兩種DFB裝置之隨泵浦強度變化的輸出發射強度及半高全寬(FWHM)。發現FWHM在高激勵強度下變得低於0.2 nm。由輸出強度中之突變來判定DFB雷射之雷射臨限值。發現基於純薄膜及摻合薄膜之裝置分別展現0.22 μJ cm^{− 2} 及0.09 μJ cm^{− 2} 之雷射臨限值。在兩種情況下，此等值低於此前針對BSBCz:CBP摻合物中之經放大自發發射(ASE)及二階DFB雷射所報導的臨限值(2 -6 )，支援混合階光柵用於高效能有機固態雷射之可能性。章節 C . 光學增益 根據此等實驗ASE資料，可判定淨增益及損失係數且其值列於表S4中。表 S4 . 脈衝寬度、激勵功率、淨增益及損失係數。

此等ASE結果提供明確證據表明，在CW狀態下在基於BSBCz之薄膜中可達成較大淨光學增益。因此，此明確地支援吾人之陳述：BSBCz為CW雷射及準CW雷射之最好候選之一。章節 D . 瞬態吸收 圖27A中之結果指示PL強度在幾個μs照射之後保持恆定。此暗示裝置中不存在藉由STA對單重態激子之淬滅。圖27C亦展示雷射與三重態吸收光譜之間不存在顯著光譜重疊。彼等結果提供明確的證據表明，用於此研究之增益介質中不存在有害的三重態損失。 根據此等資料，吾人亦估算如先前所報導之經刺激發射截面σ _em 及三重態激勵態截面σ _TT (3 ， 9 )。480 nm下之σ _em 為2.2×10^{− 16} cm² ，其明顯大於為3.0×10^{− 19} cm² 之σ _TT ，指示三重態吸收對長脈衝狀態幾乎無影響。 吾人分別估算溶液中之三重態壽命(τ _TT )、三重態吸收截面(σ _TT )及系統間穿越產率(f _ISC )，τ _TT =5.7×10³ s^-1 ，σ _TT =3.89×10^-17 cm² (在630 nm下，圖27D)且f _ISC =0.04。藉由瞬態吸收與作為參考之二苯甲酮相比較之激勵功率相依性(圖27E)來估算f _ISC (9 )。然而，應著重指出，使用吾人之瞬態吸收量測系統，吾人在薄膜中不能觀測到任何三重態比重。舉例而言，由於f _PL 值接近100%，摻合薄膜中之系統間穿越係可忽略的。 總體而言，經量測高於E _th 之發射光譜並不會大部分與三重態吸收光譜重疊，從而產生長脈衝狀態中之光放大之較大淨增益。因此，吾人確信BSBCz為CW雷射及準CW雷射之最好候選之一。章節 E . 熱模擬 為了探測裝置內之溫度分佈，使用COMSOL 5.2a執行瞬態2D熱傳遞模擬。圖38展示雷射裝置之幾何結構之示意圖。應注意，吾人忽略了此模擬中之光柵。 溫度分佈之控制局部差分方程式經表示為：

其中ρ 為材料密度，C _p 為比熱容，T 為溫度，t 為時間，k 為熱導率且Q 為雷射熱源項。雷射泵浦光束具有高斯(Gaussian)形狀。由於雷射光束之圓形對稱性，在圓柱形座標中求解熱傳遞方程式。對於脈衝式高斯雷射光束，如下編寫熱源(10 )：

其中a 為吸收係數，R 為泵浦光束在裝置之底部小平面處之反射，P 為到達增益區域之入射泵浦功率，r 及z 為空間座標，r₀ 為泵浦雷射光束之1/e ² 半徑，r =0為雷射光束之中心，z _g 為增益區域與頂部層之間的界面的z座標(參見圖38)，H (t )為具有脈衝寬度t _p 之矩形脈衝函數，h _g 為增益區域中所吸收的在在無雷射場(11 )之情況下轉換為熱量的泵浦功率之分率，其由下式給出：

其中f _PL 為螢光量子產率(f _PL (BSBCz：CBP)=86%)，λ _{泵 浦} 為泵浦雷射波長，且λ _雷射 為經提取雷射波長。關於在徑向方向之邊界條件，在旋轉軸處使用對稱性邊界條件。在底部、頂部及邊緣表面處應用熱絕緣邊界條件(忽略空氣對流)。裝置之半徑經設定成2.5 mm。功率密度為2 kW/cm² 。表S5呈現用於自COMSOL資料庫獲取之模擬的熱物理參數及幾何參數。對於BSBCz：CBP層，吾人選擇用於有機材料的與Ref (11)中相同之熱參數。表 S5 . 材料之熱物理參數及幾何參數。

在吸收泵浦雷射能量之後，BSBCz層充當熱源。藉由朝向頂部層及底部層傳導而傳遞所產生的熱。1.1 脈衝寬度變化 圖39及圖40分別展示在每次用10、30及40 ms之脈衝寬度t _p 進行泵浦之後的最大溫度上升及在BSBCz/CYTOP層之界面處的溫度上升。 此等模擬結果論證，由長脈衝泵浦照射引起的溫度上升隨脈衝持續時間增加，但此效應針對長於30 ms之脈衝傾向於飽和。亦可自此等計算看出，並未預期溫度上升會隨著入射脈衝之數目顯著增加。1.2 在 10 ms 脈衝寬度之情況下之囊封之影響 圖41中之模擬結果提供對於用於吾人之裝置中以改良在長脈衝光照射下操作之裝置中之熱管理的囊封之重要性的明確證據。1.3 CYTOP 厚度變化 如圖42中所展示，由於CYTOP之低熱導率，增加CYTOP厚度導致增益區域中之溫度之增加。儘管發現藉由CYTOP囊封DFB雷射對於改良裝置在長脈衝光激勵下之效能至關重要，但CYTOP之不良熱傳導明顯為限制因素，且此態樣在將來研究中應經由選擇更恰當的囊封材料而解決，以便展現實際CW有機半導體技術。參考文獻 1. D. Yokoyama, A. Sakaguchi, M. Suzuki, C. Adachi, Horizontal orientation of linear-shaped organic molecules having bulky substituents in neat and doped vacuum-deposited amorphous films.Org. Electron .10 (1), 127-137 (2009). 2. A. S. D. Sandanayaka, K. Yoshida, M. Inoue, K. Goushi, J. C. Ribierre, T. Matsushima, C. Adachi, Quasi-continuous-wave organic thin film distributed feedback laser.Adv. Opt. Mater. 4 , 834-839 (2016). 3. H. Nakanotani, C. Adachi, S. Watanabe, R. 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Quantum Electron. 30 (4), 89-153 (2006).[ 5 ] 電驅動有機半導體雷射二極體 概述 儘管在光學泵浦有機半導體雷射之效能及其應用方面有重大進步，但尚未實現電驅動有機雷射二極體。此處，吾人報導有機半導體雷射二極體之第一次論證。所報導之裝置將混合階分散式回饋SiO₂ 光柵併入至有機發光二極體結構中。可將高達3.30 kA cm^{− 2} 之電流密度注入至裝置中，且觀測到藍色雷射高於約0.54 kA cm^{− 2} 之臨限值。有機半導體雷射二極體之實現主要係歸因於對於在雷射波長下未展示三重態吸收損失之高增益有機半導體之選擇及在高電流密度下對電致發光效率滾降之遏制。此表示有機電子裝置領域之重大進步及朝向實現有機光電電路之完全整合之新穎的有成本效益的有機雷射二極體技術的第一步。詳細描述 由於高增益有機半導體材料之研發及高品質因數共振器結構之設計兩者中之重大進展，在過去二十年內極大地改良了光學泵浦有機半導體雷射(OSL)之屬性^1-5 。作為雷射之增益介質之有機半導體之優點包括其高光致發光量子產率(PLQY)及較大經刺激發射截面、其化學可調諧性、其跨越可見區域之寬廣的發射光譜及其易於製造性。由於低臨限值分散式回饋(DFB) OSL中之最新進展，論證藉由電驅動奈秒脈衝式無機發光二極體之光學泵浦，提供朝向新的緊湊且低成本的可見雷射技術之途徑⁶ 。此種類型之微型化有機雷射在晶片實驗室應用、化學感測及生物分析中尤其具有前景。然而，為達成有機光子電路與光電電路之完全整合，需要電驅動有機半導體雷射二極體(OSLD)，其迄今為止仍係未實現的科學挑戰。阻止雷射直接電泵浦有機半導體裝置之問題主要係歸因於來自電觸點之光學損失及發生在高電流密度下之額外三重態及極化子損失^4,5,7-9 。已提出解決此等問題之不同方法，該等方法涉及(例如)使用三重態淬滅劑^{10 - 12} 以藉由單重態-三重態激子互毀遏制三重態吸收損失及單重態淬滅，以及減小裝置作用面積¹³ 以在空間上分離激子形成與激子輻射衰變區域且將極化子淬滅製程減至最少。考慮到目前先進技術的光學泵浦有機半導體DFB雷射⁵ 之效能，伴有裝置結構之最佳化之此等方法之謹慎的組合可導致來自有機薄膜之電驅動雷射發射。 先前研究建議，若與電泵浦相關聯之額外損失經完全遏制，則將需要高於幾個kA/cm² 之電流密度以達成自OSLD之雷射¹⁴ 。在展示經放大自發發射(ASE)臨限值低於0.5 μJ/cm² 之不同有機半導體薄膜中，⁵ 用以觀測電泵浦下之雷射發射之最具前景的分子中之一者為4,4'-雙[(N-咔唑)苯乙烯基]聯苯(BSBCz) (參見圖43中之化學結構)¹⁵ 。基於BSBCz之薄膜之ASE臨限值經報導為在800 ps脈衝光激勵下低至0.30 μJ cm^{−2 16} 。同時，另一工作展示在利用5 μs之脈衝寬度之脈衝操作下，高達2.8 kA cm^{− 2} 之電流密度可注入基於BSBCz之有機發光二極體(OLED)中¹³ 。此等裝置展示高於2%的最大電致發光外部量子效率(EQE)值。此外，藉由將電流注入/輸送區域之一個尺寸縮小至50 nm而大體上減少在高電流密度下由於單重態-熱量及單重態-極化子互毀引起的效率滾降。最近，在經光學泵浦之基於BSBCz的有機DFB雷射中論證在80 MHz下之準連續波雷射及持續至少30 ms之真實連續波雷射¹⁷ 。可達成此類前所未有的效能，係因為在4,4'-雙(N-咔唑基)-1,1'-聯苯(CBP)摻合物中，BSBCz之PLQY接近100%，且係因為在BSBCz薄膜之雷射波長下不存在顯著三重態吸收損失。此處，吾人藉由將反向OLED結構與整合於裝置之作用區域中之混合階DFB SiO₂ 光柵相組合來論證來自BSBCz薄膜之電驅動雷射發射，因此提供來自有機半導體之電驅動雷射發射之第一明確證據。 此研究中研發之OSLD之製造方法及架構示意性地展示於圖43至圖45中(參見材料及方法章節中之實驗程序之詳細描述)。首先將100 nm厚的介電SiO₂ 層濺鍍至預清潔之圖案化氧化銦錫(ITO)玻璃基板上。隨後吾人設計一階布拉格散射區域由二階布拉格散射區域包圍的混合階DFB光柵，該等區域分別產生強光學回饋及提供雷射發射之高效垂直提取^17,18 。在DFB雷射中，眾所周知，在滿足布拉格條件^4,19 (mλ_Bragg = 2n_eff Λ)時發生雷射振盪，其中m為繞射階，l _Bragg 為布拉格波長，n_eff 為增益介質之有效折射率，且Λ為光柵週期。使用所報導的用於BSBCz之n_eff 值及l _Bragg 值^20,21 ，混合階(m=1, 2) DFB雷射裝置之光柵週期經計算分別為140 nm及280 nm。使用電子束微影及反應性離子蝕刻將此等混合階DFB光柵雕刻在SiO₂ 層中之140×200 μm面積內(圖46A)。如藉由圖46B中之掃描電子顯微法(SEM)影像所展示，此工作中製造的DFB光柵具有140±5 nm及280±5 nm之週期及約65±5 nm之光柵深度，其完美地符合以上提供之吾人之規範。各1階及2階DFB光柵之長度分別為約10 µm及15.1 µm。隨後執行能量色散X射線光譜儀(EDX)分析，以確保在光柵製造期間ITO層並未損壞且確保在蝕刻區域中完全移除SiO₂ 層。圖46C及圖46D中所展示之EDX結果提供證據表明，自ITO至沈積於DFB光柵之頂部上的有機半導體層的電荷注入可發生於ITO觸點所定位之蝕刻區域中。另外，吾人提出亦可使用低成本之簡單奈米壓印微影製程製備DFB共振器(圖45)。如藉由圖47A中所顯示的示意性表示所展示，在此工作中製造的OSLD具有以下蒸氣沈積於DFB光柵之頂部上之簡單反向OLED結構：ITO (100 nm)/20wt.%Cs:BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm)。在此類反向裝置結構中，在接近ITO觸點之區域中藉由Cs摻雜BSBCz薄膜改良至有機層中的電子注入，而MoO₃ 用作電洞注入層(圖48至圖49)。如圖50中所展示，所有層之表面形態呈現具有20 nm至30 nm之表面調變深度的光柵結構。儘管最有效之OLED大體上使用多層架構以使電荷平衡達到最佳^22,23 ，但電荷積聚可發生在高電流密度下之有機異質界面處，其可對裝置效能及穩定性不利²⁴ 。在此工作中所製造的OSLD僅含有BSBCz作為有機半導體且經特定設計以使有機異質界面的數目降至最低。應注意亦製造不具有SiO₂ DFB光柵之裝置，且用作獲取關於光柵對電致發光屬性的影響的另外資訊的參考。此外，吾人渴望在SiO₂ 、ITO及聚合物中或作用層頂部製作具有不同一維DFB共振器結構的有機半導體雷射二極體(圖51A至圖51D)。如圖52中所展示，具有二維DFB共振器結構之有機半導體雷射二極體對較低臨限值之2D DFB雷射亦具有前景。 圖47B及圖53A至圖53D展示OSLD之光學顯微鏡影像，且圖47C展示不具有光柵之參考OLED之彼等光學顯微鏡影像，其兩者均在4.0 V之直流電(DC)操作下。電致發光自參考OLED之作用面積均勻發射。在OSLD之情況下，可自OSLD之2階DFB光柵區域看見更劇烈的發射，其經特定設計以促進垂直光提取。在具有或不具有DFB光柵之代表性裝置中量測的電流-電壓(J-V)及EQE-J曲線展示於圖47D至圖47E中。裝置在DC及脈衝(具有500 ns之電壓脈衝寬度及100 Hz之重複率)條件兩者下表徵。根據SEM及雷射顯微鏡影像估算OSLD之作用面積，其有必要計算注入至裝置中之電流密度。在DC及脈衝操作下之參考裝置在裝置崩潰之前分別展示70 A cm^{− 2} 及850 A cm^{− 2} 之最大電流密度(J_max )。由於較小有效裝置區域^13,25 之焦耳熱之減小，在DC及脈衝操作下OSLD明顯地分別呈現80 A cm^{− 2} 及3220 A cm^{− 2} 之較高J_max 。發現所有BSBCz裝置在較低電流密度下呈現高於2%之最大EQE值。然而，在DC操作之高於15 A cm^{− 2} 之電流密度下觀測到OSLD及參考裝置中顯著的效率滾降，其可歸因於有機增益介質之熱降解。在脈衝操作下，參考裝置展示在高於410 A cm^{− 2} 之電流密度下的效率滾降，其符合先前報導¹³ 中之結果。更重要地，在脈衝操作下遏制OSLD中之效率滾降且甚至發現EQE大體上增加至高於800 A cm^{− 2} 以達成3.3%之最大值。當電流密度增加至高於3200 A cm^{− 2} 時，EQE快速減少推測歸因於有機半導體之熱降解。 如圖54中所展示，參考裝置之電致發光光譜類似於BSBCz純薄膜之穩態PL光譜且不隨電流密度之變化而變化。圖53E、圖55A、圖55C及圖56A展示在脈衝操作之不同電流密度下若干OSLD之電致發光光譜之演變。在垂直於基板平面之方向上自OSLD之ITO側量測此等光譜。可以明顯看出，當J變得高於800 A cm^{− 2} 時在456.8 nm下產生強光譜線窄化效應。為進行進一步瞭解，輸出強度及半高全寬(FWHM)隨電流密度變化繪製於圖53F、圖55B、圖55D及圖56B中。而BSBCz純薄膜之穩態PL光譜之FWHM為約35 nm，其在最高電流密度下值減小至低於0.2 nm。同時，亦觀測到輸出強度之斜坡效率之突變，其與EQE-J曲線之狀態相符且可用於判定960 A cm^{− 2} 之臨限值。類似於EQE-J曲線中所見，當J ＞ 3.2 kA cm^{− 2} 時，輸出強度隨J減小，歸因於熱降解導致裝置崩潰。在此狀態中，然而，值得注意的係OSLD之發射光譜保持極其陡。所觀測到的狀態明顯地表明光放大在高電流密度下產生且OSLD展示雷射發射高於雷射臨限值。 對已與過去的幾個有爭論的報導相關聯之第一有機半導體雷射二極體之探索，意味著在主張此研究中製造的OSLD之前應加以重視提供電驅動雷射發射⁹ 。首先，幾個研究^{20 , 26 , 27} 表明自有機發光裝置之波導模式之邊緣發射可導致極強的線窄化效應而不雷射放大。對比此等先前工作，在垂直於基板平面之方向上檢測到自吾人之OSLD之發射且展示明確的臨限值狀態。亦應著重指出，有機薄膜之ASE線寬通常在幾個nm範圍內，而有機DFB雷射之FWHM可遠低於1 nm⁵ 。在FWHM低於0.2 nm的情況下，自吾人之OSLD之發射光譜不能僅歸因於ASE且對應於通常在光學泵浦有機DFB雷射中所獲得的要素。其次，先前報導藉由無意激勵ITO中之轉變表明極窄發射光譜。²⁸ ITO之原子光譜線包括在410.3 nm、451.3 nm及468.5 nm下之彼等。²⁹ 圖55A中之OSLD之發射峰波長為456.8 nm，其不能歸因於自ITO之發射。亦應強調，OSLD之發射應為共振器模式之特性，且因此輸出應對雷射腔之任何修改極敏感。調諧光學泵浦有機DFB雷射中之發射波長的一種簡單方式為改變光柵週期^{4 , 5 , 30 , 31} 。圖55C至圖55D顯示在不同電流密度下之發射光譜及針對分別具有300 nm(針對2階散射)之光柵週期及150 nm(針對1階散射)之光柵週期之OSLD輸出強度隨電流密度變化。此裝置展示在475.5 nm下FWHM低至0.16 nm及臨限值為1.07 kA cm^{− 2} 之雷射峰(圖57)。 另外，吾人基於採用經改良共振器設計之BSBCz薄膜展示有機DFB雷射(圖58)。由於藉由二階光柵提取之雷射輻射表示損失通道，此等雷射通常展示相比於其一階對應物之較高臨限值。為研究提取與臨限值之間的平衡點，吾人製造出具有不同寬度及具有一階及二階區域之光柵。根據雷射輸入-輸出曲線推論之臨限值且根據圖59中之二階區域之寬度繪製。可以看出，振盪臨限值隨二階區域之大小線性增加。此可理解為就雷射臨限值而言其與波導損失成正比，其隨遞增週期線性變大。從而，混合階共振器之臨限值隨提取光之分率增加而增加，但即使對於強提取，臨限值保持較低。藉由變化光柵參數，因此有機固態雷射可經調適而具有最佳化屬性(低臨限值及高提取)。 圖56B顯示在不同電流密度下之發射光譜及針對分別具有300 nm(針對2階散射)之光柵週期及150 nm(針對1階散射)之光柵週期及4個一階週期及12個二階週期之OSLD輸出強度隨電流密度變化(圖60)。此裝置展示在500.5 nm下FWHM低至0.18 nm及臨限值為540 A cm^{− 2} 之雷射峰。此明確提供證據表明，自吾人之OSLD之雷射發射很大程度上受DFB共振器結構影響，且此可用於調諧波長範圍內之雷射波長。自OSLD之雷射發射亦應遵循一些關於輸出光束偏光、輸出光束之形狀及時間相干⁹ 之準則。如圖61中所展示，OSLD之輸出光束很大程度上沿光柵圖案線性偏光，提供電驅動裝置中真實一維DFB雷射動作之明確證據。 需要澄清之另一重要問題為看出電驅動OSLD之雷射臨限值如何與藉由光學泵浦獲得的雷射臨限值相比較。圖62展示在405 nm之激勵波長下藉由遞送500 ns脈衝之雷射二極體通過ITO側之OSLD光學泵浦之雷射特性。在481 nm處出現雷射發射，其與電驅動雷射波長相符合。在光學泵浦下量測之雷射臨限值為約450 W cm^{− 2} ，其高於在不具有兩個電極之經光學泵浦基於BSBCz的DFB雷射中獲得的36 W cm^{− 2} 之值。應注意用於OSLD之不同層之厚度在此工作已最佳化以將由於此等電極之存在的光學損失降至最低。假設在高電流密度下之BSBCz OSLD操作中無額外損失機制，在經光學泵浦裝置中量測的臨限值表明電驅動雷射發射應實現電流密度高於1125 A cm^{− 2} 。用於光學及電學泵浦之類似臨限值表明已幾乎遏制在高電流密度³² 下大體上發生在有機電致發光裝置中之額外損失(包括激子互毀、三重態及極化子吸收、由高電場之淬滅、焦耳熱)。此與在劇烈脈衝電激勵下未在OSLD中觀測到電致發光效率滾降之實情完全相符。為解釋此種結果，應記住BSBCz薄膜在雷射/ASE波長下不展示顯著三重態吸收，且其藉由單重態-三重態互毀呈現單重態之極弱淬滅。重要地，先前工作表明裝置作用面積還之減小可用於自激子輻射衰變分離激子形成且大體上降低極化子/熱淬滅製程。 吾人亦製造在一個晶片上具有九個DFB之裝置如圖63中所展示，且此種裝置提供雷射發射之有效輸出。對於低臨限值有機半導體雷射二極體，吾人亦成功地製造了圓形DFB共振器(圖64至圖65)。 總之，此研究論證電驅動有機半導體雷射二極體之第一實現，該電驅動有機半導體雷射二極體實施混合階分散式回饋SiO₂ 共振器至有機發光二極體結構之作用面積中。特定而言，裝置展示出臨限電流密度低至540 A cm^{− 2} 之藍色雷射發射。關於發射線寬、偏光及臨限值之不同準則可用以區分雷射發射與已仔細檢驗及充分支援此係有機半導體中電驅動雷射之首次觀測的主張的其他現象。此報導開拓有機光子之新機會及視角，且應明顯地充當有機半導體雷射二極體技術之將來發展的強基礎，該有機半導體雷射二極體技術應用簡單、便宜及可調諧雷射源及其用於基於有機的光電平台之完全及直接整合的適合性的優點。材料及方法 裝置製造及特性 使用中性清潔劑、純水、丙酮及異丙醇藉由超音波處理接著藉由UV臭氧處理清潔經氧化銦錫(ITO)塗佈之玻璃基板(100 nm ITO,Atsugi Micro Co.)。在室溫下將100 nm厚SiO₂ 濺鍍於100 nm經ITO塗佈玻璃基板上以將DFB雕刻於ITO基板上。在濺鍍期間氬氣壓力為0.2 Pa。RF功率設定為100 W (圖43及圖44)。再次使用異丙醇藉由超音波處理接著藉由UV臭氧處理清潔基板。藉由在4000 rpm下旋塗15 s，用六甲基二矽氮烷(HMDS)來處理二氧化矽表面且在120℃下退火120 s。自ZEP520A-7溶液(ZEON Co.)將具有約70 nm之厚度的抗蝕劑層以4000 rpm旋塗於基板上持續30 s，且在180℃下烘烤240 s。使用具有0.1 nC cm^{− 2} 之經最佳化劑量的JBX-5500SC系統(JEOL)進行電子束微影以將光柵圖案繪製於抗蝕劑層上。在電子束照射之後，在室溫下將圖案於顯影劑溶液(ZED-N50，ZEON Co.)中顯影。將經圖案化之抗蝕劑層用作蝕刻遮罩，同時使用EIS-200ERT蝕刻系統(ELIONIX)用CHF₃ 電漿蝕刻基板。為自基板完全移除抗蝕劑層，使用FA-1EA蝕刻系統(SAMCO)用O₂ 電漿蝕刻基板。蝕刻條件經最佳化以自DFB之間距調變完全移除SiO₂ 直至ITO接觸。使用SEM (SU8000，Hitachi)觀測形成於二氧化矽表面上之光柵(圖46B)。執行EDX (在6.0 kV下，SU8000，Hitachi)分析以確認自DFB之間距完全移除SiO₂ (圖46C及圖46D)。 藉由習知超音波處理清潔DFB基板。隨後藉由在2.0 × 10^{− 4} Pa之壓力下之熱蒸發以0.1 nm s^{− 1} 至0.2 nm s^{− 1} 之總蒸發速率將有機層及金屬電極真空放置在具有SiO₂ 絕緣體之DFB基板上以製造具有氧化銦錫(ITO) (100 nm)/20 wt% Cs：BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm)結構之i-OLED。留在ITO表面之SiO₂ 層充當絕緣體。因此，OLED之電流區域受限於BSBCz與ITO直接接觸之DFB區域。具有140 × 200 µm之作用面積的參考OLED亦使用相同電流區域製備。使用累計球系統(A10094，Hamamatsu Photonics)在室溫下量測OLED之電流密度-電壓-EQE (J-V-EQE)特性(DC)。使用脈衝產生器(NF，WF1945)、放大器(NF，HSA4101)及光電倍增管(PMT) (C9525-02，Hamamatsu Photonics)在脈衝驅動下量測J -V -L 特性。在多通道示波器(Agilent Technologies, MSO6104A)上監測PMT回應及驅動方波信號兩者。在具有變化峰值電流之裝置中施加具有500 ns之脈衝寬度、5 μs之脈衝週期及100 Hz之重複頻率的長方形脈衝。光譜量測 利用光纖收集垂直於裝置表面之經發射雷射光，該光纖連接至多通道光譜儀(PMA-50，Hamamatsu Photonics)且置放為與該裝置相距3 cm。對於CW操作，使用CW雷射二極體(NICHIYA，NDV7375E，最大功率為1400 mW)生成具有405 nm之激勵波長的激勵光。在此等量測中，使用以脈衝產生器(WF 1974，NF Co.)觸發之聲光調變器(AOM，Gooch&Housego)來遞送脈衝。經由透鏡及狹縫將激勵光集中於裝置之4.5×10^{− 5} cm² 之面積上，且使用與數位攝影機(C9300，Hamamatsu Photonics)連接之具有100 ps之時間解析度的條框眼(C7700，Hamamatsu Photonics)收集所發射的光。使用光電倍增管(PMT) (C9525-02，Hamamatsu Photonics)來記錄發射強度。在多通道示波器(Agilent Technologies, MSO6104A)上監測PMT回應及驅動方波信號兩者。如前所描述，針對此量測使用相同的照射及偵測角度。所有量測係在氮氣氛圍中進行，以防止由濕氣及氧氣引起之任何降解。參考文獻 1. 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The pursuit of electrically-driven organic semiconductor lasers.J. Mater. Chem. C 2 , 2827-2836 (2014). 9. Samuel, I. D. W., Namdas, E. B. & Turnbull, G. A. How to recognize lasing.Nature Photon. 3, 546-549 (2009). 10. Sandanayaka, A. S. D.et al. Improvement of the quasi-continuous-wave lasing properties in organic semiconductor lasers using oxygen as triplet quencher.Appl. Phys. Lett. 108 , 223301 (2016). 11. Zhang, Y. F. & Forrest, S. R. Existence of continuous-wave threshold for organic semiconductor lasers.Phys. Rev. B 84 , 241301 (2011). 12. Schols, S.et al. Triplet excitation scavenging in films of conjugated polymers.Chem. Phys. Chem. 10 , 1071-1076 (2009). 13. Hayashi, K.et al. Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm.Appl. Phys. Lett. 106 , 093301 (2015). 14. Gärtner, C.et al. The influence of annihilation processes on the threshold current density of organic laser diodes.J. Appl. 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Mater. 25 , 6801-6827 (2013).分散式回饋電驅動有機雷射之電學模擬 1. 裝置模型及參數 在此研究中，使用所謂的「第一代模型」描述有機發光二極體(OLED)中之電荷輸送。在此模型中，使用二維時間無關漂移擴散模型藉由自洽求解電子密度n 、電洞密度p 及靜電電位Ψ。泊松(Poisson)方程式將靜電電位Ψ與空間電荷密度相關聯，如下:

其中F為向量電場，q為基本電荷，ε_r 為材料之相對電容率且ε₀ 為真空電容率，

為電子(電洞)濃度，

為經填充電子(電洞)陷阱狀態之濃度。假設拋物線能態密度(DOS)及Maxwell-Boltzmann統計，電子及電洞濃度表示為：

其中

及

為最低未佔用分子軌域(LUMO)及最高佔用分子軌域(HOMO)中之載流子之能態密度，

及

為LUMO及HOMO之能量位準，

及

為電子及電洞之準費米位準(quasi Fermi level)，

為Boltzmann常數且T為裝置溫度。 有機半導體中電荷載流子陷阱之存在係由於結構缺陷及/或雜質。經注入電荷需首先在建立電流之前填充此等陷阱。此狀態稱作陷阱限制電流(TLC)。^1,2 指數或高斯分佈用於模型化有機半導體內之陷阱分佈。³ 在此工作中，使用用於電洞陷阱狀態之高斯分佈：^{4 , 5}

其中

為陷阱之總密度，

為高於HOMO位準之能量陷阱深度，且

為分佈之寬度。藉由求高斯能態密度乘以Fermi-Dirac分佈之積分估算經捕獲電洞之密度。 藉由電場F中之漂移及由於電荷密度梯度之擴散控制電荷輸送。漂移-擴散近似法中電子及電洞之穩態連續方程式由下式給出：

其中

為電子(電洞)遷移率，

為電子(電洞)擴散常數，且R 為重組速率。電荷載流子遷移率推測為場相關且具有Pool-Frenkel形式：^6,7

其中

為零場遷移率，且

為電子(電洞)之特性場。在此模型中不考慮高能混亂，因此吾人假設愛因斯坦關係式(Einstein's relation)之有效性以根據電荷遷移率計算擴散常數。藉由Langevin模型⁸ 給出重組速率R ：

當電子與電洞重組時，其形成激子。所產生之激子可在輻射式或非輻射式衰變之前隨特性擴散常數D_s 遷移。單重態激子之連續方程式由下式給出：

其中S 為激子密度。第一時期為根據電子電洞重組之單重態激子產生速率，其為1/4，第二時期表示激子擴散，第三時期表示隨輻射衰變常數

及非輻射衰變常數

之激子衰變，且最後一個時期表示藉由具有場相關解離速率

之電場之激子的解離，其由Onsager-Braun模型給出：^9,10

其中

為激子半徑，

為激子結合能，

為一階Bessel函數，且

為場相關參數。在此模型內，電場淬滅(EFQ)之衝擊取決於激子結合能

。2. 模擬結果及與實驗之比較 2.1. 單極及雙極參考裝置 在進行雙極裝置模擬之前，考慮純電洞及純電子裝置以便測試電學模型、模擬參數及電荷載流子遷移率。純電子裝置由包夾在Cs (10nm)/Al與20 wt% Cs：BSBCz (10nm)/ITO電極之間的190 nm BSBCz層構成。藉由將10 nm MoO₃ 層插入BSBCz (200 nm)與ITO及Al兩者之間獲得純電洞裝置。雙極OLED裝置包含以下結構：ITO/20 wt% Cs：BSBCz (10 nm)/BSBCz (190 nm)/MoO₃ (10 nm)/Al。陰極(ITO/20 wt% Cs：BSBCz)之功函數取值為2.6 eV，且陽極(MoO₃ /Al)中之一功函數為5.7 eV。此等裝置結構之能量位準圖式展示於圖48中。 使用所報導之BSBCz之電荷載流子遷移率(由飛行時間量測) [11]。圖49a展示用於BSBCz之電子及電洞之經量測經報導之遷移率及與Pool-Frenkel場相關模型對應的擬合。在下表中展示經擬合遷移率參數之值以及電模擬所需之輸入參數之其他值。BSBCz之電洞及電子遷移率為差不多相同數量級，指示BSBCz可輸送兩者類型之電荷載流子。 表. 電模擬參數

單極及雙極裝置之實驗及模擬J ( V ) 曲線展示於圖49b中。在直流電(DC)驅動下所量測之實驗J 低於18V ，且在脈衝驅動下高於18V 。純電洞裝置電流很大程度上受V ＜ 20 V 處之陷阱限制。藉由模擬之實驗資料之最佳化獲得的

、

及

之值在上表中給出。結果展示單極裝置之實驗與模擬之間的良好吻合。對於雙極裝置，在較低電流密度下量測與模擬之間的小偏差係歸因於實驗漏電流之存在。模擬模型預測在高電壓下純電洞裝置及純電子裝置具有類似電流密度，展示良好的電子及電洞傳輸平衡。雙極裝置展示比單極電流密度高一個數量級的電流密度。2.2. 雙極 DFB 裝置 DFB光柵共振器之使用不但藉由為光放大^{12 - 14} 提供正光學回饋影響有機雷射之光學性質，而且影響有機雷射之電學特性。計算奈米結構化陰極對DFB OLED之電學特性之影響且與參考OLED (不具有光柵)相比較。DFB OLED之結構與雙極OLED類似，差異在於奈米結構化陰極由沈積於ITO上之週期性光柵SiO₂ -Cs：BSBCz組成。光柵週期為280 nm且光柵深度為60 nm，如圖66a中所表示。在此結構中，BSBCz之厚度為150 nm。為進行比較，製造具有相同厚度之參考OLED (ITO/20 wt% Cs：BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Al)且不具有光柵。已保留用於雙極裝置之所有參數及條件，因為DFB及參考OLED不具有額外的擬合參數。 DFB光柵及參考OLED之實驗及模擬J ( V ) 曲線展示於圖66b中。電模擬預測在DC(V ＜ 18 V )及脈衝式操作(V ≥18 V ) 兩種情況下J ( V ) 曲線與實驗結果良好吻合。 除J ( V ) 曲線預測之外，電模擬可以存取實體參數，該等實體參數難以在實驗上進行判定，諸如電荷載流子密度之空間分佈、電場及重組區域之位置。 首先，吾人考慮參考OLED。圖67a至圖67b展示在10V及70V下參考OLED之電荷載流子分佈及電場剖面。自由電子自ITO/CS：BSBCz陰極注入至BSBCZ中 (在x = 0 μm 時)，且自由電洞自Al/MoO₃ 陽極注入(x = 0 . 215 μm )。由於載流子重組，當其離開觸點時載流子密度減低。當n = p 時，電場增加且達到其中心的最大值。在10V下，藉由接近陰極及陽極之高電荷載流子密度篩選電場。在較高電壓(70V )下，電子穿透得更深且陽極附近的電場仍然較高。 在DFB光柵OLED之情況下，在70V 下提取實體參數。圖68a至圖68b展示電荷載流子密度n及p之空間分佈。由於陰極之週期性奈米結構化電子未均一地注入，其空間分佈遵循週期性注入，如圖68b、圖68c中可清楚地看出。電洞自均一陽極注入且在塊體中相對均一地延伸(圖68a、圖68c)。當電洞到達陰極時，其對於參考OLED衰變(圖67(b))。然而，由於SiO₂ 光柵之存在，電洞在SiO₂ /BSBCz之界面處積聚且展示高密度(圖68a)。 圖69a展示電場之週期性剖面，其在絕緣體中較高且在BSBCz層中稍微調變對於參考OLED (約3.5×10⁶ V / cm )保持相同強度。圖69b中所展示之電流密度剖面在很大程度上經調變且展示在SiO₂ /Cs：BSBCz界面附近之較高值。 為澄清SiO₂ /Cs：BSBCz界面附近之高電流密度值之原因，重組速率剖面R 表示於圖70a中。如吾人可看出，R 亦展示裝置內部之週期性變化。在由陰極/陽極定界的區域中，剖面與參考OLED之剖面相同，而其在由SiO₂ /陽極定界的區域中減小(參見圖70c)。在Cs：BSBCz/SiO₂ 界面處，R 展示由於電洞及電子積聚之最大值，如圖70d中所論證。 裝置內部之電場為約MV/cm² ，如圖69a中所表示。因此，由電場引起的激子解離不可忽略且在很大程度上影響裝置效能。有機半導體之單重態激子結合能在0.3 eV至1.6 eV^{15 - 18} 之範圍內。在低電場下，主導的去活化製程為輻射衰變及非輻射衰變。在高電場下，激子解離之機率極大增加且取決於激子結合能。為了考慮電場誘導激子解離，由方程式10給出的場相關解離速率包括於單重態激子連續性方程式9中。圖71a展示參考裝置之經計算激子密度S ，包括具有不同激子結合能E_b (0 . 2 - 0 . 6 eV ) 之EFQ。當E_b 減低時，EFQ變成嚴重損失機制。使用具有高激子結合能之分子需要克服EFQ。使用PL淬滅產率實驗估算BSBCz之激子結合能且其下限為0 . 6 eV 。 圖71b展示針對參考裝置及DFB裝置之具有或不具有電場誘導激子解離之S ( J ) 特性。在不具有EFQ的情況下，S隨J 增加且展示在J = 3KA / cm² 時就DFB裝置之9×10¹⁷ cm ^{- 3} 而言相對於參考裝置之2×10¹⁷ cm ^{- 3} 之高值。S 中之此種不同來自不同裝置架構，其導致裝置內部之不同R 分佈，如圖70a、70b中所展示。藉由考慮EFQ模型及BSBCz之E_b = 0 . 6 eV ，兩種裝置之S 均增加，且直至J = 0 . 5KA / cm² 則接著由於激子之電場解離而減小。DFB裝置中之EFQ比參考裝置中之EFQ稍低，且可解釋相比於圖47E中所展示之參考裝置，DFB裝置之實驗性低EQE滾降。 為了獲得對DFB裝置中EQE增強之原因的進一步實體瞭解，具有或不具有EFQ之參考裝置內部之一維激子分佈展示於圖72a中。在DFB裝置之情況下，不具有及具有EFQ之二維激子分佈分別展示於圖72b、圖72c中。 裝置(圖74，底部)中之激子密度分佈(圖73，右下)與光模分佈之比較指示在第2光柵區域處其間存在較大重疊，有助於光放大。該顯著重疊必然有助於較低雷射臨限值。 在參考裝置中，在缺失EFQ之情況下，S 均一地分散。在存在EFQ之情況下，由於高電場(其在塊體中達到3.5MV / cm )，塊體中之S 減少(參見圖79b)。接近Cs：BSBCz/ITO界面，電場較低，其避免激子之EFQ。在DFB裝置之情況下，激子自兩個重組位點(位點1及位點2)產生，如圖71a中所展示。接近SiO₂ 光柵之電荷之積聚建立具有高激子密度(S =6×10¹⁷ cm ^{- 3} )之重組區域，命名為位點1。位點2具有與參考裝置(S =1×10¹⁷ cm ^{- 3} )相同的S 。在不具有EFQ的情況下，最大值S 由位點1提供，且解釋在低電場下相比於參考裝置，DFB裝置中之高值(參見圖71b)。當考慮EFQ時，位點1中之激子由此位點中之高電場淬滅(F = 3 . 5MV / cm )，且最大值S 由位點2提供，其中接近該界面之電場較低(F = 1 . 2MV cm )且在塊體區域中相對於參考裝置逐漸增加。從而，接近該界面之一些激子可存活，若其未經另一機制(吾人未包括於此模擬中)淬滅。參考文獻 1. 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Phys. , vol. 143, no. 24, pp. 1-8, 2015.[ 6 ] 極低經放大自發發射臨限值及自旋塗八茀純薄膜之藍色電致發光 在過去的二十年期間有機半導體雷射已成為深入研究之主題，導致關於雷射臨限值及操作性裝置之穩定性的重大發展。^{1 - 3} 此等裝置目前考慮用於多種應用，包括光譜工具、資料通信裝置、醫療診斷學及化學傳感器。^{1 - 5} 然而，目前尚無電驅動有機雷射二極體之論證且亦仍需進行突破以開發真實連續波光學泵浦有機半導體雷射技術。^1-3,6-8 線已很好地認識到實現電泵浦有機雷射二極體之挑戰，且其涉及(i)由於極化子及長壽命三重態，在雷射波長下發生額外吸收損失，(ii)由於單重態-三重態、單重態-極化子及單重態-熱互毀，單重態激子之淬滅，及(iii)在高電流密度下之電致發光裝置操作中有機材料之穩定性。應注意，已提出降低三重態及極化子損失之方法，其包括使用三重態淬滅劑及減小有機發光二極體(OLED)之作用面積以在空間上分離激子形成與激子衰變區域。^9,10 儘管此等問題需要充分克服且仍需進一步研究，但亦至關重要的係同時在有機半導體薄膜中大體上降低經放大自發發射(ASE)及雷射之臨限值。³ 為此目的，需要新穎高雷射增益有機材料以及可併入至電泵浦有機發光裝置中之經改良共振器結構之發展。 輻射衰變速率(k_R )直接與愛因斯坦B係數相關，如以下方程式所表示：

，其中ν ₀ 為光之頻率，h 為Planck's常數，且c 為光之速度。ASE臨限值與B係數成反比，意味著較大k_R 通常較佳以達成低ASE臨限值。^{11 , 12} 如最近審閱之關於有機雷射之文章中所概述，³ 基於小分子的有機薄膜中所報導之最低ASE臨限值為110 nJ/cm² ，且使用9,9'-螺茀衍生物獲得。¹³ 在約300至400 nJ/cm² 之薄膜中展示低ASE臨限值之兩種其他優良有機半導體雷射材料為4,4'-雙[(N - 咔唑)苯乙烯基]聯苯(BSBCz)及七茀衍生物。^12,14 儘管ASE臨限值通常取決於用於光學泵浦之光源之特性，但值得注意的係上文所提及之ASE臨限值藉由使用用於光激勵之類似氮雷射而判定。認為茀衍生物對於達成低ASE臨限值係極具前景的，且該等茀衍生物中之一部分展示高於1×10⁹ s^{- 1} 之輻射衰變速率。^{13 - 19} 明顯地，先前工作已具體研究經己基側鏈官能化的三聯茀、五茀及七茀衍生物之光物理屬性。¹⁸ 結果論證當增加寡聚茀分子之長度時，輻射衰變速率增加而ASE臨限值減小。在此情形下，驗證藉由增加寡聚物長度ASE/雷射屬性是否能再進行進一步改良至關重要。 此處，吾人就八茀衍生物進行報導，展示在具有87%之PLQY及約600 ps之螢光壽命之經旋塗純薄膜中無濃度淬滅。此分子之化學結構顯示於圖75a中。八茀純薄膜之大PLQY值及短PL壽命伴有約90 nJ/cm² 之ASE臨限值，到達有機非聚合增益介質中ASE效能之前所未有的位準。³ 基於八茀純薄膜之有機分散式回饋(DFB)雷射及OLED之效能提供進一步證據證明，此茀衍生物對致力於有機半導體雷射裝置及其應用之進一步工作極具前景。 用於此工作中之實驗程序描述於補充材料中。¹⁹ 旋塗於熔融矽石基板上之八茀純薄膜之吸收及穩態PL光譜展示於圖75b中。薄膜在波長之可見範圍內幾乎透明，且在紫外輻射區域中呈現具有375 nm之最大吸收峰波長的一個主要吸收帶。此吸收峰先前已歸因於茀單體之間的激子耦合。¹⁸ 自長波長吸收邊緣之光能間隙經計算為約2.9 eV。插圖75b中所展示之PL光譜及圖像指示八茀純薄膜發藍色螢光。光譜展示具有兩個波峰的明確電子振動結構，其可指派給(0，0)及(0，1)轉變及在與(0，2)轉變相關聯之較長波長下之肩部。發現最大PL峰波長為約423 nm。在含有分散至4,4'-雙(N - 咔唑基)-1,10-聯苯(CBP)主體中之10 wt.%及20 wt.%之八茀的旋塗摻合物中所量測的吸收及穩態PL光譜顯示於圖76中(參見補充材料)。在此工作中選定CBP主體，此係因為已知高效Förster型能量傳送自CBP發生至大部分寡聚茀衍生物。¹⁴ 儘管摻合物之吸收光譜由CBP吸收控制，但可以看出其PL光譜並不與八茀純薄膜之光譜明顯不同。隨後在純薄膜及CBP摻合物中量測PLQY及PL壽命。10 wt.%及20 wt.%之摻合物分別展示88%及87%之PLQY值，其與純薄膜中發現的值接近。純薄膜及10wt.%及20wt.%之摻合物亦呈現類似的單指數螢光衰變，其分別具有609、570及611 ps之特性PL壽命(參見補充材料中之圖77)。此提供證據表明，八茀純薄膜並不展示任何PL濃度淬滅，不同於在類似三聯茀、五茀及七茀衍生物中所報導的。¹⁸ 考慮到在八茀純薄膜中所量測之約1.7×10⁹ s^{- 1} 之較大輻射衰變速率，此寡聚茀衍生物可預期展示優良的ASE屬性。^{11 , 12} 使用可變角橢圓偏振光譜法來量測八茀純薄膜之光學常數且展示於圖75c中(自橢圓偏振法資料計算光學常數，可見於補充材料中之圖78中)。純薄膜之較小光學各向異性指示八茀分子幾乎隨機取向，其與先前報導之七茀純薄膜中之橢圓偏振法結果相符。²⁰ 如圖79a中示意性地表示，八茀純薄膜之ASE屬性藉由在10 Hz之重複率下遞送800 ps脈衝之氮雷射在337 nm處光學泵浦樣本而表徵。激勵光束集中至尺寸為0.5 cm×0.08 cm之條帶中，且自有機薄膜之邊緣收集PL。圖79b展示在各種泵浦強度下自260 nm厚八茀純薄膜之邊緣量測的PL光譜。在高激勵密度下可明確看出光譜線窄化效應，伴有半高全寬(FWHM)降至5 nm，提供證據表明ASE產生於此樣本中。光放大發生在約450 nm處，歸因於在有機膜中經波導且藉由經經刺激發射放大的自發地發射的光子。²¹ 隨後根據自薄膜之邊緣發射之輸出強度相對於激勵強度之曲線判定ASE臨限值。可見於圖79c中之斜坡效率之突變導致約90 nJ/cm² 之ASE臨限值。應注意，在具有在53 nm與540 nm之間的範圍內的不同薄膜厚度之八茀純薄膜中量測ASE屬性。圖79d及圖80中所展示之資料(參見補充資訊)指示260 nm之厚度的薄膜之ASE臨限值最低。已在聚(9,9-二辛基茀)薄膜中報導ASE臨限值之類似厚度相關性。²² 此種狀態歸因於當增加厚度時模式限制之增加與泵浦模式重疊之減少之間的相互作用。明顯地，在260 nm厚八茀純薄膜中所量測之ASE臨限值低於曾在基於小分子的有機薄膜中所報導的最低值。³ 此種良好的效能亦應意指八茀薄膜呈現極低的損失係數值。為此目的，根據八茀薄膜之邊緣與泵浦條帶之間的距離量測ASE強度。圖81中所展示之結果(參見補充資訊)導致對於260 nm厚八茀純薄膜之5.1 cm^-1 之損失係數。此種低值接近聚(9,9-二辛基茀)薄膜²³ 中所報導之低值，且提供八茀薄膜之優良光學波導屬性之證據。應著重指出，不同於大多數聚茀系統，由於茀酮之形成，八茀以及大多數基於茀的小分子^{24 - 26} 在劇烈的光照射下並不展示其光物理屬性之任何顯著退化。此外，圖82中所顯示之結果(參見補充資訊)論證八茀純薄膜在環境氛圍及氮氛圍兩者中在高於ASE臨限值之高泵浦強度下呈現優良的光穩定性。此可涉及薄膜之高輻射衰變速率，其推測導致在高強度照射下材料之光致漂白之減少。比較在較短寡聚茀中所量測之ASE臨限值，^14,18 結果表明增加寡聚物長度導致ASE效能之改良。然而，應注意在十茀薄膜進行之初步實驗展示比在八茀薄膜獲得之ASE臨限值更高的ASE臨限值，指示八茀衍生物在此系列寡聚物中當然為有機半導體雷射之最具前景的候選。 吾人隨後設計及製造一種由藉由一階散射區域包圍的二階布拉格散射區域組成的混合階DFB光柵結構。¹⁷ 此種光柵架構經選擇以獲得低雷射臨限值連同在垂直於基板之方向上的雷射發射。在DFB雷射中，雷射發射在布拉格波長(λ _Bragg )附近發生，定義為：mλ _Bragg = 2n _eff Λ，其中n _eff 為雷射增益介質之有效折射率，m 為布拉格階且L為光柵週期。^1-3 使用藉由橢圓偏振法判定之八茀純薄膜之折射率(圖75c)及在此研究中量測之ASE波長，對於m =1，2，分別選擇光柵週期為260 nm及130 nm。圖83a及圖83b展示此類DFB SiO₂ 光柵之示意性表示及掃描電子顯微鏡(SEM)影像，使用電子束微影及反應性離子蝕刻技術製造此類光柵。應注意DFB光柵之深度為約70 nm。為完成雷射裝置，將260 nm厚的八茀純薄膜旋塗於DFB結構頂部上。圖83c展示在低於及高於雷射臨限值之若干激勵密度下垂直於基板平面所偵測的發射光譜。低於臨限值，可觀測到歸因於DFB光柵之光學阻帶之布拉格突降。高於雷射臨限值，在約452 nm之雷射波長處可清楚看出陡雷射發射峰。根據激勵強度之此DFB雷射之輸出發射強度及FWHM繪製於圖81d中。發現雷射發射峰之FWHM在高激勵密度下低於0.3 nm。同時，發現根據輸出強度曲線之斜率中之變化判定之雷射臨限值為約84 nJ/cm² ，其比先前所報導之ASE臨限值稍低。總體而言，此工作中量測之極低ASE及雷射臨限值連同在高光激勵強度下薄膜之優良的光穩定性論證此八茀衍生物為用於有機半導體雷射應用之極具前景的增益介質材料。 為充分評估用於有機雷射二極體之此八茀衍生物之潛能，使用標準OLED結構研究此化合物在純薄膜及CBP摻合物中之電致發光(EL)屬性亦至關重要。此研究中製造之OLED之示意性表示提供於圖82a中。該等裝置之架構如下：氧化銦錫(ITO) (100 nm)/聚(3,4-伸乙二氧基噻吩)：聚(苯乙烯磺酸鹽) (PEDOT：PSS) (45 nm)/EML(約40 nm)/2,8-雙(二苯基磷醯基)二苯并[b,d]噻吩(PPT) (10 nm)/2,2',2''-(1,3,5-苯三基)-參(1-苯基-1-H-苯并咪唑) (TPBi) (55 nm)/LiF (1 nm)/Al (100 nm)，其中發光層(EML)對應於八茀純薄膜抑或八茀：CBP摻合物。在此等裝置中，PEDOT：PSS起電洞注入層的作用，而PPT及TPBi分別用作電洞阻擋層及電子傳輸層。圖84a中之PEDOT：PSS、PPT及TPBi之最高佔用分子軌域(HOMO)及最低未佔用分子軌域(LUMO)能量值取自文獻。²⁰ 藉由光電子光譜分析在空氣中量測之八茀純薄膜之游離電位為5.9 eV(參見補充材料中之圖85)。使用自純薄膜之吸收光譜判定之2.9 eV之光學帶隙值，八茀之電子親和力可估算為約3 eV。如圖86a中所展示(參見補充資訊)，在此等OLED中在10 mA / cm² 處量測之EL光譜與八茀純薄膜中及CBP摻合物中所量測之PL光譜類似，指示自此等裝置發射之藍色EL僅來自八茀發色團。裝置之電流密度-電壓-亮度(J -V -L ) 曲線顯示於圖86b中(參見補充資訊)。在1 cd/m² 處，基於純八茀薄膜之OLED、10 wt.% CBP摻合物及20 wt.% CBP摻合物分別呈現5.0 V、4.9 V及4.5 V之驅動電壓。在此等OLED中獲得之最高亮度值對於純薄膜為4580 cd/m² (在12.6 V處)，對於20 wt.%摻合物為8520 cd/m² (在10.4 V處)，且對於10 wt . %摻合物為8370 cd/m² (在11.2 V處)。根據電流密度之裝置之外部量子效率(η_ext )繪製於圖84b中。發現其最大值對於純薄膜為3.9%，對於20 wt.%摻合物為4.3%，且對於10 wt.%摻合物為4.4%。不能藉由三種薄膜之PLQY值解釋效率之不同，其PLQY值幾乎相同。實情為，致力於旋塗薄膜中寡聚茀分子之分子定向的當前研究論證表明，儘管八茀分子在純薄膜中隨機定向，但20 wt.%及10 wt.%八茀：CBP摻合物展示八茀分子之相對良好的水平定向。²⁶ 發射偶極之此等水平分子定向應導致光提取效率之改良，且因此可解釋基於CBP摻合物在OLED中量測之稍高的η_ext 值。^{20 , 26} 在有機雷射二極體之情形下，在此等OLED中獲得之最大η_ext 值明顯具有前景。然而，應注入更高的電流密度至裝置中且在高於100 mA/cm² 之電流密度下出現效率滾降，此種效率滾降在另外工作中需經由在慎重地將此八茀衍生物考慮為電驅動有機雷射裝置之候選之前改良裝置架構進行遏制。 概言之，此研究論證非聚合有機薄膜中前所未有的90 nJ/cm² 之低ASE臨限值。使用在旋塗純薄膜中展示87%之PLQY及1.7 × 10⁹ s^{- 1} 之大輻射衰變速率之八茀衍生物實現此成就。此藍光發射材料接著用於低臨限值有機半導體DFB雷射中及具有外部量子效率高達4.4%且最大亮度值接近10,000 cd/m² 之螢光OLED中。總體而言，此研究提供證據表明此八茀衍生物為用於有機半導體雷射之優良的有機材料。 參見補充材料[URL將藉由AIP插入]關於用於此研究之實驗程序中之所有資訊，八茀薄膜中之CBP摻合物之吸收及螢光光譜、橢圓偏振法資料、額外ASE特性化結果，及HOMO及LUMO之判定。參考文獻 1. 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Nakanotani, L. Mager, S. Mery and C. Adachi, Chem. Comm. 52, 3103 (2016). 25. J. C. Ribierre, A. Ruseckas, O. Gaudin, I. D. W. Samuel, H. S. Barcena, S. V. Staton and P. L. Burn, Org. Electron. 10, 803 (2009). 26. L. Zhao, T. Komino, D. H. Kim, M. H. Sazzad, D. Pitrat, J. C. Mulatier, C. Andraud, J. C. Ribierre and C. Adachi, J. Mater. Chem. C 4, 11557 (2016).實驗程序 光物理及 ASE 量測 遵循先前文獻中所公開的方法合成該八茀衍生物。¹ 使用清潔劑、純水、丙酮及異丙醇藉由超音波處理接著藉由紫外輻射臭氧處理清潔熔融矽石基板。八茀純薄膜及CBP：八茀摻合薄膜藉由旋塗自經氮填充之手套箱中之氯仿溶液沈積於熔融矽石基板上。應注意，變化溶液之濃度及自旋速度以控制八茀純薄膜之厚度。分別使用UV-vis光譜光度計(Perkin-Elmer Lambda 950-PKA)及光譜螢光計(Jasco FP-6500)來量測吸收及穩態發射光譜。使用具有340 nm之激勵波長之氙氣燈及累計球(C11347-11 Quantaurus QY，Hamamatsu Photonics)來量測薄膜中之PLQY。使用條框攝影機及遞送具有10 ps之寬度及365 nm之波長之光學脈衝的Ti-藍寶石雷射系統(Millenia Prime，Spectra Physics)來量測PL衰變。 在45°至75°之不同角度處藉由75 nm厚的八茀純薄膜中之步驟5°進行可變角橢圓偏振光譜法(VASE) (J.A. Wollam，M-2000U)。接著使用分析軟體(J.A .Woollam,WVASE32)分析橢圓偏振法資料以判定薄膜之各向異性消光係數及折射率。 對於ASE屬性之特性化，藉由337 nm處發射之脈衝式氮雷射(KEN2020，Usho)光學泵浦樣本。此雷射在10 Hz之重複率下遞送具有800 ps之脈衝持續時間之脈衝。使用一組中性密度濾光器變化泵浦光束強度。泵浦光束集中至0.5 cm × 0.08 cm之條帶中。使用連接至電荷耦合裝置光譜儀(PMA-11，Hamamatsu Photonics)之光纖收集來自有機薄膜之邊緣的發射光譜。有機 DFB 雷射之製造及特性化 遵循如上之相同清潔程序清潔具有熱生長1 μm厚的SiO₂ 層的矽基板。隨後將六甲基二矽氮烷(HMDS)旋塗於SiO₂ 表面之頂部上且樣本在120℃下退火2分鐘。此後，自ZEP520A-7溶液(ZEON Co.)將70 nm厚的抗蝕劑層旋塗於基板上，且在180℃下退火4分鐘。接著，電子束微影使用JBX-5500SC系統(JEOL)用於將DFB光柵圖案化於抗蝕劑層上。電子束照射之後，圖案在顯影劑溶液(ZED-N50，ZEON Co.)中顯影。在以下步驟中，經圖案化抗蝕劑層起蝕刻遮罩的作用。使用EIS-200ERT蝕刻系統(ELIONIX)藉由CHF₃ 電漿蝕刻基板。最後，使用FA-1EA蝕刻系統(SAMCO)藉由O₂ 電漿-經蝕刻基板以完全移除抗蝕劑層。SEM (SU8000，Hitachi)用於檢查DFB光柵之品質。為完成有機雷射裝置，最後將260 nm厚的八茀純薄膜自氯仿溶液旋塗於DFB光柵之頂部上。 對於雷射操作，經由透鏡及狹縫將來自氮氣雷射(SRS，NL-100)之脈衝式激勵光集中於裝置之6 × 10^{− 3} cm² 之面積上。激勵波長為337 nm，脈衝寬度為3.5 ns，且重複率為20 Hz。激勵光相對於裝置平面之法線成約20°入射於裝置上。利用連接至多通道光譜儀(PMA-50，Hamamatsu Photonics)之光纖收集垂直於裝置表面之經發射光，該光纖經置放為與該裝置相距6 cm。使用一組中性密度濾光器來控制激勵強度。OLED 之製造及特性化 藉由在預清潔ITO玻璃基板上沈積有機層及陰極製造OLED。在此研究中製造之OLED之結構如下：ITO(100 nm)/PEDOT：PSS(45 nm)/EML(約40 nm)/PPT(10 nm)/TPBi(55 nm)/LiF(1 nm)/Al(100 nm)，其中發光層(EML)對應於八茀純薄膜抑或八茀：CBP摻合物。PEDOT：PSS層旋塗於ITO上且在130℃下退火30分鐘。八茀純薄膜及摻合薄膜自氯仿溶液旋塗於手套箱環境中之PEDOT：PSS層之頂部上。EML層之厚度通常為約40 nm。接著，10 nm厚的PPT層及40 nm厚的TPBi層藉由熱蒸發而沈積。最後，由薄LiF層及100 nm厚的Al層製成之陰極藉由通過遮蔽罩之熱蒸發來製備。裝置之作用面積為4 mm² 。在特性化之前，裝置囊封於氮氛圍中以防止與氧氣及濕氣相關的任何降解效應。 在直流電驅動下，使用電源錶(Keithley2400，Keithley Instruments Inc.)及絕對外部量子效率量測系統(C9920-12，Hamamatsu Photonics)來量測電流密度-電壓-亮度(J -V -L )特性。使用連接至光譜儀(PMA-12，Hamamatsu Photonics)之光纖來量測EL光譜。參考文獻 1. R. Anemian, J.C. Mulatier, C. Andraud, O. Stephan, J.C. Vial, Chem. Comm. 1608 (2002).[ 7 ] 經 CW 放大自發發射 ( ASE ) 實驗 經CW放大自發發射(ASE)實驗在雙茀心樹枝體及八茀旋塗純薄膜中進行。薄膜沈積至預清潔平面熔融矽石基板上且未經囊封。薄膜厚度為約250 nm。 為研究CW ASE之屬性，在355 nm處藉由CW雷射二極體光學泵浦薄膜。使用以脈衝產生器(WF 1974，NF Co.)觸發之聲光調變器(AOM，Gooch&Housego)來遞送具有不同寬度之脈衝。使用與數位攝影機(C9300，Hamamatsu Photonics)連接之具有100 ps之時間解析度的條框眼(C7700，Hamamatsu Photonics)自薄膜之邊緣收集所發射的光。使用光電倍增管(PMT) (C9525-02，Hamamatsu Photonics)來記錄發射強度。在多通道示波器(Agilent Technologies, MSO6104A)上監測PMT回應及驅動方波信號兩者。 在兩種材料中，各種泵浦強度下之條框攝影機影像及發射光譜展示高於臨限值之明確的線窄化效應，其係歸因於經刺激發射且可指派給ASE。根據比較針對不同脈波寬度之激勵強度曲線之輸出強度量測ASE臨限值。結果展示針對在100 μs至5 ms之範圍內變化的脈波寬度ASE臨限值幾乎保持不變。此外，可以注意到此等ASE臨限值與使用脈衝式氮雷射(800 ps之脈衝寬度及10 Hz之重複率)在此等材料中所量測之彼等臨限值相符。在八茀及雙茀心樹枝體兩者中達成CW雷射之可能性意指可忽略的三重態損失。此與兩種材料均呈現極高的光致發光量子產率(PLQY)(雙茀心樹枝體中92%之PLQY及八茀純薄膜中82%之PLQY)之實情相符。此外，在八茀及雙茀心樹枝體溶液中進行瞬態吸收量測以檢查三重態-三重態吸收光譜。可以看出，ASE與三重態吸收光譜之間不存在重疊，其提供明確證據表明三重態吸收並不對兩種材料中之CW雷射起任何有害的作用。[ 8 ] 電流注入有機半導體雷射二極體 概述 本雷射二極體主要基於無機半導體，但藉由獨特的製造路線有機物亦可為優良的增益介質。然而，儘管光學泵浦有機半導體雷射已取得進步，但目前尚未實現電驅動有機半導體雷射二極體。此處，吾人報導有機半導體雷射二極體之第一論證。裝置併入有機發光二極體結構中之混合階分散式回饋SiO₂ 光柵且發射藍色雷射。此等結果證明將電流直接注入有機薄膜之雷射可藉由選擇在雷射波長下未展示三重態及極化子吸收損失之高增益有機半導體及設計恰當的回饋結構以遏制高電流密度下之損失來實現。此表示朝向簡單的基於有機物的雷射二極體的第一步，其可涵蓋可見光譜及近紅外光譜，且為朝向將來有機光電積體電路之主要進步。詳細描述 由於高增益有機半導體材料之發展及高品質因數共振器結構^{1 - 5} 之設計兩者之重大進步，在過去二十年內極大地改良了光學泵浦有機半導體雷射(OSL)之屬性。作為雷射之增益介質之有機半導體之優點包括其高光致發光(PL)量子產率、較大經刺激發射截面，及跨越可見區域之寬廣的發射光譜以及其化學可調諧性及易於處理。由於低臨限值分散式回饋(DFB) OSL之最新進步，論證了藉由電驅動奈秒脈衝式無機發光二極體之光學泵浦，提供一種朝向新型緊湊及低成本可見雷射技術⁶ 之路線。此種類型之微型化有機雷射對於晶片實驗室應用極具前景。然而，最終目標為電驅動有機半導體雷射二極體(OSLD)。除使有機光子及光電電路能夠完全整合之外，OSLD之實現將打開高效能顯示、醫療感測及生物相容裝置之新穎的應用。 藉由有機半導體之直接電泵浦阻止雷射之實現之問題主要歸因於自電觸點之光學損失及發生在高電流密度^4,5,7-9 下之三重態及極化子損失。已提出解決此等基本損失問題之方法，該等方法包括使用三重態淬滅劑^{10 - 12} 藉由單重態-三重態激子互毀以遏制三重態吸收損失及單重態淬滅，以及減小裝置作用面積¹³ 以在空間上分離激子形成與激子輻射衰變出現且將極化子淬滅製程降至最低。然而，即使有機發光二極體(OLED)及光學泵浦有機半導體DFB雷射⁵ 中已取得進步，但仍未確鑿地論證電流注入OSLD。 先前研究建議若與電泵浦相關聯之額外損失經完全遏制¹⁴ ，則需要高於幾個kA/cm² 之電流密度以達成自OSLD之雷射。實現OSLD之最具前景之分子中之一者為4,4'-雙[(N - 咔唑)苯乙烯基]聯苯(BSBCz) (圖89a中之化學結構)¹⁵ ，此係因為其光學特性及電學特性之優良的組合(諸如薄膜(在800 ps脈衝光激勵下為0.30 µJ cm^{− 2} )¹⁶ 中之低經放大自發發射(ASE)臨限值)及耐受在5 µs脈衝操作下具有高於2%¹³ 之最大電致發光(EL)外部量子效率(η _EQE )之OLED中高達2.8 kA cm^{− 2} 之電流密度注入的能力。此外，最近在經光學泵浦之基於BSBCz之DFB雷射¹⁷ 中論證在80 MHz之重複率下及在30 ms之長脈衝光激勵下之雷射且由於在BSBCz薄膜之雷射波長下極小的三重態吸收損失該雷射係很可能的。此處，吾人無庸置疑地論證來自有機半導體薄膜之雷射之第一實例，該雷射基於在具有整合於裝置之作用面積中之混合階DFB SiO₂ 光柵之反向OLED結構中的BSBCz薄膜經由OSLD之發展及完整特性化藉由電直接激勵。 此研究中研發之OSLD之架構及製造示意性地展示於圖89a及圖90中(參見材料及方法之實驗程序之詳細描述)。氧化銦錫(ITO)玻璃基板上之SiO₂ 之濺鍍層藉由電子束微影及反應性離子蝕刻雕刻以建立具有30 × 90 µm之面積的混合DFB光柵(圖89b)，且有機層及金屬陰極真空沈積於基板上以完成裝置。吾人設計具有一階及二階布拉格散射區域之混合階DFB光柵，其分別提供雷射發射之強光學回饋及高效垂直提取^{17 , 18} 。基於布拉格條件^{4 , 19} ，mλ _Bragg =2n _eff Λ _m ,分別針對一階及二階區域選擇140 nm及280 nm之光柵週期(Λ₁ 及Λ₂ )，其中m 為繞射階，λ _Bragg 為布拉格波長，其設定成對於BSBCz之所報導之最大增益波長(477 nm)，且n _eff 為增益介質之有效折射率，其經計算對於BSBCz^{20 , 21} 為1.70。在經表徵之第一集合裝置中個別一階及二階DFB光柵區域之長度分別為1.12 µm及1.68 µm，下文被稱作OSLD。 圖89c及圖89d中之掃描電子顯微法(SEM)影像確認經製造DFB光柵具有140±5 nm及280±5 nm之週期，具有約65±5 nm之光柵深度。完全移除經蝕刻區域中之SiO₂ 層以曝露ITO對與有機層進行良好電接觸至關重要且藉由能量色散X射線光譜儀(EDX)分析驗證(圖90c、圖90d)。完整OSLD之截面SEM及EDX影像展示於圖89d及圖89e中。所有層之表面形態展示具有50 nm至60 nm之表面調變深度之光柵結構。儘管共振雷射模式與電極之相互作用預期降低回饋結構之品質因數，但金屬電極上之此種光柵結構亦應降低裝置結構^{22 ， 23} 內導引之模式之吸收損失。 此工作中製造之OSLD具有擁有能量位準之簡單反向OLED結構ITO (100 nm)/20 wt.% Cs：BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm)，如圖91a中所展示。在接近ITO觸點之區域中將BSBCz薄膜與Cs摻雜改良注入至有機層之電子，且MoO₃ 用作電洞注入層(圖92)。儘管最有效之OLED大體上使用多層架構以使電荷平衡^24,25 達到最佳，但在高電流密度下電荷可在有機異質界面處積聚，其可對裝置效能及穩定性²⁶ 有害。在此工作中所製造的OSLD僅含有BSBCz作為有機半導體層且經特定設計以使有機異質界面的數目降至最低。亦製造不具有SiO₂ DFB光柵之參考裝置(下文被稱作OLED)以研究光柵對EL屬性之影響。 圖91b展示在3.0 V之直流電(DC)操作下OSLD及參考OLED之光學顯微鏡影像。除先前所描述之DFB光柵之外，五個其他DFB光柵幾何形狀(表1)經最佳化且表徵於OSLD中。儘管EL自參考OLED之作用面積均勻發射，但可自OSLD中之二階DFB光柵區域看出更劇烈的發射，其經特定設計以促進垂直光提取(圖91b及圖93)。在環境溫度下在脈衝式條件(400 ns之電壓脈衝寬度及1 kHz之重複率)下OSLD及OLED中之電流密度-電壓(J -V )及η _EQE -J 特性展示於圖91c及圖91d中，且在DC條件下獲得之特性顯示於圖94中。用於計算OSLD之電流密度之作用面積根據SEM及雷射顯微鏡影像估算。 在裝置崩潰之前參考OLED之最大電流密度自在DC操作下之6.6 A cm^{− 2} 增加至在脈衝操作下之5.7 kA cm^{− 2} ，此係因為藉由脈衝操作^13,27 經減小之焦耳加。在DC操作下，裝置中之所有者在較低電流密度下呈現高於2%之最大η _EQE 且在高於1 A cm^{− 2} 之電流密度下呈現強效率滾降，其推測歸因於裝置之熱降解。另一方面，在脈衝操作(圖91c、圖91d)下OLED中之效率滾降在高於110 A cm^{− 2} 之電流密度處開始，與先前報導¹³ 相符。在脈衝操作下OSLD中之效率滾降經進一步遏制，且甚至發現η _EQE 實質上增加至高於200 A cm^{− 2} 以達成2.9%之最大值。在高於2.2 kA cm^{− 2} 之電流密度下η _EQE 快速減低很可能係由於裝置之熱降解。 儘管OLED之EL光譜類似於純BSBCz薄膜之穩態PL光譜(圖94c)且不隨電流密度之變化而變化，但來自OSLD之玻璃表面之EL光譜在脈衝操作下顯現隨遞增之電流密度之光譜線窄化(圖95a)。在478.0 nm處對於低於650 A cm^{− 2} 之電流密度觀測到對應於DFB光柵之阻帶之布拉格突降(圖95b)。當電流密度增加至高於此值時，在480.3 nm處產生強光譜線窄化，表明雷射之開始。發現窄發射峰之強度比EL發射背景之強度增加得更快，其可歸因於與經刺激發射相關聯之非線性。 根據電流之OSLD之輸出強度及半高全寬(FWHM)繪製於圖95c中。儘管純BSBCz薄膜之穩態PL光譜之FWHM為約35 nm，但OSLD之FWHM在高電流密度減小至低於0.2 nm之值，其接近吾人之光譜儀(對於57 nm之波長範圍為0.17 nm)之光譜解析度限制。輸出強度之斜坡效率隨遞增之電流驟變且可用於判定600 A cm^{− 2} (8.1 mA)之臨限值。在高於4.0 kA cm^{− 2} 之情況下，輸出強度隨遞增之電流減小，推測歸因於溫度之強增加導致裝置崩潰開始，但發射光譜保持極陡。此增加及後續減小與η _EQE -J 曲線相符。藉由置放於OSLD前部與ITO玻璃基板(圖95d)相距3 cm之距離的功率計量測之最大輸出功率在3.3 kA cm^{− 2} 處為0.50 mW。此等觀測到的EL屬性很大程度上表明光放大在高電流密度下產生且電驅動雷射在高於電流密度臨限值之情況下實現。 光束偏光及形狀經表徵以提供進一步證據表明此係雷射⁹ 。OSLD之輸出光束很大程度上沿光柵圖案經線性偏光(圖96a)，其預期雷射發射來自一維DFB。在不同電流密度下高於雷射臨限值處所量測之OSLD發射之空間剖面(圖96b)展示妥當定義的高斯光束(Gaussian beams)之存在。亦，若此係雷射應存在光斑圖案之外觀，提供空間相干性之初步證據。 在吾人可主張雷射之前，在過去被曲解為雷射之若干現象必須排除作為所觀測狀態⁹ 之起因。在垂直於基板平面之方向上檢測到吾人之OSLD之發射，且展示明確的臨限值狀態，因此由不具有雷射放大之波導模式之邊緣發射引起的線窄化可不予考慮^20,28,29 。ASE可以與雷射類似之方式出現，但吾人之OSLD (＜ 0.2 nm)中之FWHM比有機薄膜(幾個奈米)之典型的ASE線寬窄得多，且與經光學泵浦的有機DFB雷射(＜ 1 nm)⁵ 之典型的FWHM相符。藉由無意激勵ITO中之轉變所獲得之極窄的發射光譜亦被誤認為來來自有機層³⁰ 之發射。然而，圖95a中之OSLD之發射峰波長為480.3 nm，且不能歸因於來自ITO之發射，其在410.3 nm、451.3 nm及468.5 nm處具有原子光譜線。³¹ 若此真實地係來自DFB結構之雷射，則OSLD之發射應為共振器模式之特性，且輸出應對雷射腔之任何修改極敏感。因此，具有不同DFB幾何結構之OSLD (標記OSLD-1至OSLD-5 (表1)經製造及表徵(圖93)以確認發射波長可經可預測地調諧，其在經光學泵浦的有機DFB雷射^4,5,32,33 中很常見。OSLD、OSLD-1、OSLD-2及OSLD-3之雷射峰幾乎相同(分別為480.3 nm、479.6 nm、480.5 nm及478.5 nm)，其具有相同DFB光柵週期。此外，OSLD-1、OSLD-2及OSLD-3所有者具有較低最小FWHM (分別為0.20 nm、0.20 nm及0.21 nm)及明確的臨限值(分別為1.2 kA cm^{− 2} 、0.8 kA cm^{− 2} 及1.1 kA cm^{− 2} )。另一方面，具有不同DFB光柵週期之OSLD-4及OSLD-5在459.0 nm處顯現具有0.25 nm之FWHM及1.2 kA cm^{− 2} 之臨限值(OSLD-4)，及在501.7 nm處具有0.38 nm之FWHM及1.4 kA cm^{− 2} 之臨限值(OSLD-5)之雷射峰。此等結果明確地論證雷射波長由DFB幾何結構控制。 為驗證電驅動OSLD之雷射臨限值與藉由光學泵浦所獲得的雷射臨限值相符，使用遞送3.0 ns脈衝之N₂ 雷射(337 nm之激勵波長)量測經由ITO側光學泵浦之OSLD (OLSD-6)之雷射特性(圖97)。在光學泵浦(481 nm)下OLSD-6之雷射峰與在電泵浦(480.3 nm)下OSLD之雷射峰相符。在光學泵浦下所量測之雷射臨限值為約430 W cm^{− 2} 。儘管此值高於在不具有兩個電極¹⁷ 之經光學泵浦的基於BSBCz之DFB雷射中所獲得之30 W cm^{− 2} 之值，但本OSLD中之層之厚度經最佳化以將由電極之存在引起的光學損失降至最低。假設在高電流密度下OSLD-6中無額外的損失機構，在電泵浦下1.1 kA cm^{− 2} 之雷射臨限值可根據在光學泵浦下之臨限值估算。此值與在電泵浦下在具有相同光柵週期(OSLD及OSLD-2)之較小裝置中所量測之臨限值(0.6至0.8 kA cm^{− 2} )合理地吻合。 此等結果表明在高電流密度³⁴ 下通常發生在OLED中之額外損失(包括激子互毀、三重態及極化子吸收、由高電場引起之淬滅，及焦耳加熱)在BSBCz OSLD中幾乎已經遏制。此與EL效率滾降並非在劇烈脈衝電激勵下之OSLD中觀測之實情充分相符。可基於BSBCz及裝置之屬性解釋損失之遏制。如先前所提及，BSBCz薄膜並不展示顯著的三重態損失³⁵ ，且裝置作用面積之減小導致焦耳熱輔助之激子淬滅³⁶ 之減少。此外，基於分別量測複合薄膜BSBCz：MoO₃ 及BSBCz：Cs針對BSBCz中之自由基陽離子及自由基陰離子兩者極化子吸收與發射光譜之間的重疊係可忽略的(圖98)。 執行裝置之電學及光學模擬以進一步確認電流注入雷射發生在OSLD中(圖99)。使用自單極裝置之實驗資料之擬合提取之載流子遷移率(圖99a，圖99b)，具有或不具有光柵之裝置之模擬J -V 曲線與實驗特性極好地吻合(圖99a、圖99c、圖99d)，指示與具有光柵之裝置之良好電接觸之足夠的蝕刻。重組速率剖面(圖99e，圖99f)展示裝置內部之週期性變化，此係因為電子自ITO電極經由絕緣SiO₂ 光柵之週期性注入。類似於該重組，激子密度(圖100a)遍佈有機層之厚度，但主要集中於其中SiO₂ 不妨礙陰極至陽極之路徑的區域中。OSLD及OLED (圖99g)之平均激子密度類似，指示接近SiO₂ 之激子之高積聚補償導致相對於參考裝置之類似激子密度的光柵(無注入區域)之間的低激子密度。 自二階光柵之光提取及ITO層中形成波導損失之光陷阱在OSLD中之經計算共振波長l ₀ = 483 nm處之光場之經刺激電場分佈E (x ,y )中明確可見(圖100b)。DFB共振器腔由40%之限制因數G及255之品質因數表徵。根據激子密度分佈與光場分佈(細節參見材料及方法)之重疊計算隨電流密度變化之模態增益(g _m ) (其為雷射模式下光之放大之指示符)，具有針對2.8 10^{− 16} cm² 之BSBCz³⁵ 之經刺激發射截面σ _刺激 且針對二階區域展示於圖100c中。高於500 A cm^{− 2} 之高模態增益及遞增模態增益與雷射之觀測相符。在J =500 A cm^{− 2} 處激子密度與光模之間的強空間重疊之面積(圖100d)對應於其中激子密度及光場(圖100a，圖100b)兩者均較高之面積。因此，DFB結構亦有助於增強經由在光柵之谷值中及以上之高激子密度之定位與光模耦合。 總之，此研究證明經由恰當設計及共振器及有機半導體之選擇自電流驅動有機半導體之雷射可能遏制損失及增強耦合。該雷射論證此處已在多個裝置中再生且經充分表徵以排除可被誤認為係雷射之其他現象。該結果充分支援此係有機半導體中電泵浦雷射之第一觀測之主張。BSBCz中之低損失係啟用雷射不可或缺的，因此設計具有類似或經改良屬性之新型雷射分子之策略之發展係至關重要的下一步。此報導開拓有機光子之新機會，且充當有機半導體雷射二極體技術之將來發展的基礎，亦即簡單、便宜及可調諧且可使基於有機的光電平台能夠完全及直接整合。材料及方法 裝置製造 使用中性清潔劑、純水、丙酮及異丙醇藉由超音波處理接著藉由UV臭氧處理清潔經氧化銦錫(ITO)塗佈之玻璃基板(100 nm厚之ITO,Atsugi Micro Co.)。將100 nm厚之SiO₂ 層(其將變成DFB光柵)在100℃下濺鍍至ITO塗佈之玻璃基板上。在濺鍍期間氬氣壓力為0.66 Pa。RF功率設定為100 W。再次使用異丙醇藉由超音波處理接著藉由UV臭氧處理清潔基板。藉由在4,000 rpm下旋塗15 s，用六甲基二矽氮烷(HMDS)來處理SiO₂ 表面且在120℃下退火120 s。自ZEP520A-7溶液(ZEON Co.)將具有約70 nm之厚度的抗蝕劑層以4,000 rpm旋塗於基板上持續30 s，且在180℃下烘烤240 s。 使用具有0.1 nC cm^{− 2} 之經最佳化劑量的JBX-5500SC系統(JEOL)進行電子束微影以將光柵圖案繪製於抗蝕劑層上。在電子束照射之後，在室溫下將圖案於顯影劑溶液(ZED-N50，ZEON Co.)中顯影。將經圖案化之抗蝕劑層用作蝕刻遮罩，同時使用EIS-200ERT蝕刻系統(ELIONIX)用CHF₃ 電漿蝕刻基板。為自基板完全移除抗蝕劑層，使用FA-1EA蝕刻系統(SAMCO)用O₂ 電漿蝕刻基板。蝕刻條件經最佳化以自DFB中之凹槽完全移除SiO₂ 直至ITO曝露。使用SEM (SU8000，Hitachi)觀測形成於SiO₂ 表面上之光柵(圖89c)。執行EDX (在6.0 kV下，SU8000，Hitachi)分析以確認自DFB之間距完全移除SiO₂ (圖90c及圖90d)。使用冷場發射SEM (SU8200，Hitachi High-Technologies)、能量色散X射線光譜測定法(XFlash FladQuad5060，Bruker)及聚焦離子束系統(FB-2100，Hitachi High-Technologies)藉由Kobelco量測截面SEM及EDX (圖89d，圖89e)。 藉由習知超音波處理清潔DFB基板。隨後藉由在1.5 × 10^{− 4} Pa之壓力下之熱蒸發以0.1 nm s^{− 1} 至0.2 nm s^{− 1} 之總蒸發速率將有機層及金屬電極真空放置在基板上以製造具有氧化銦錫(ITO) (100 nm)/20 wt% BSBCz：Cs (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm)結構之OSLD。ITO表面上之SiO₂ 層充當除DFB光柵之外的絕緣體。因此，OLED之電流區域受限於BSBCz與ITO直接接觸之DFB區域。具有30 × 45 µm之作用面積的參考OLED亦使用相同電流區域製備。裝置特性化 使用玻璃蓋及UV固化環氧樹脂將所有裝置囊封於氮填充的手套箱中以防止由濕氣及氧氣引起之任何降解。使用累計球系統(A10094，Hamamatsu Photonics)在室溫下量測OSLD及OLED之電流密度-電壓-η _EQE (J-V-η _EQE )特性(DC)。對於脈衝量測，在環境溫度下使用脈衝產生器(NF，WF1945)將具有400 ns之脈衝寬度、1 µs之脈衝週期、1 kHz之重複頻率及變化峰電流之長方形脈衝施加至裝置。在脈衝驅動下藉由放大器(NF，HSA4101)及光電倍增管(PMT) (C9525-02，Hamamatsu Photonics)量測J -V -亮度特性。在多通道示波器(Agilent Technologies, MSO6104A)上監測PMT回應及驅動方波信號兩者。藉由除以根據具有校正因數之PMT回應EL強度計算的光子之數目乘以根據電流計算的注入電子之數目來計算η _EQE 。使用雷射功率計(OPHIR Optronics Solution公司，StarLite 7Z01565)量測輸出功率。 為量測光譜，利用光纖收集垂直於裝置表面之針對光學及電學泵浦OSLD之經發射雷射光，該光纖連接至多通道光譜儀(PMA-50，Hamamatsu Photonics)且置放為與該裝置相距3 cm。藉由使用CCD攝影機(beam profiler WimCamD-LCM，DataRay)來檢查OSLD之光束剖面。對於在光學泵浦下OSLD-6之特性，經由透鏡及狹縫將來自氮氣雷射(NL100，N₂ laser，Stanford Research System)之脈衝式激勵光集中於裝置之6 × 10^{− 3} cm² 之面積中。激勵波長為337 nm、脈衝寬度為3 ns，且重複率為20 Hz。激勵光相對於裝置平面之法線成約20°入射於裝置上。使用一組中性密度濾光器來控制激勵強度。使用圖98中之光譜螢光計(FP-6500，JASCO)及圖94中之光譜儀(PMA-50)監測穩態PL光譜分析。裝置模型化及參數 使用Comsol Multiphysics 5.2a軟體執行共振DFB腔之光學模擬。使用有限元方法(FEM)在Comsol軟體之射頻模塊中求解各頻率之亥姆霍茲方程式(Helmholtz equation)。各層由其複折射率及厚度表示。計算域受由經一階光柵包圍之二階光柵組成的一個超級單元限制。弗羅奎週期邊界條件應用於橫向邊界，且散射邊界條件用於頂部域及底部域。僅考慮TE模式，因為由於TM模式比TE模式經歷更多的損失(由於金屬吸收)而被遏制。 使用與泊松方程式耦合之二維時間無關漂移擴散方程式及使用Silvaco之技術電腦輔助設計(TCAD)軟體針對電荷載流子之連續性方程式描述經由OSLD之電荷輸送。使用拋物線能態密度(DOS)及Maxwell-Boltzmann統計表示電子及電洞濃度。高斯分佈用於模型化有機半導體³⁷ 內之陷阱分佈。假設電荷載流子遷移率為場相關性且具有Pool-Frenkel形式^{38 , 39} 。在此模型中不考慮高能混亂，因此吾人假設愛因斯坦關係式之有效性以根據電荷遷移率計算電荷載流子擴散常數。藉由Langevin模型⁴⁰ 給出重組速率R 。藉由考慮激子擴散、輻射及非輻射製程求解單重態激子之連續性方程式。 純電洞及純電子的實驗資料

, 其中L 為腔長度(僅二階光柵區域)且d 為作用薄膜厚度。 表1|不同OSLD幾何結構之參數

圖90中所展示之不同光柵幾何結構之參數以及用於計算電流密度之總曝露ITO面積A 之值。 表2.光學模擬及電學模擬之參數。

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[ 1 ] Continuous Wave Organic Thin Film Distributed Feedback Laser Since the discovery of organic solid-state lasers,^{[ 1 − 6 ]} Significant efforts have been devoted to the development of continuous wave (cw) lasers in organic materials, including small molecules, oligomers and polymers.^{[ 7 − 10 ]} However, operating organic solid-state lasers at very high repetition rates (quasi-cw excitation) under optical cw excitation or pulsed excitation is extremely challenging. When organic thin films are optically pumped under these conditions, accumulation of long-lived triplet excitons and charge carriers usually occurs,^{[ 11 − 14 ]} This results in increased absorption loss by triplet exciton formation and singlet exciton quenching by triplet excitons (ie singlet-triplet mutual destruction).^{[ 11 − 16 ]} These absorption losses and emission quenching are significant issues that must be addressed to achieve cw and quasi-cw operation because they cause the laser threshold to increase substantially and in worst case completely stop the laser.^{[ 17 − 19 ]} To curb absorption loss and emission quenching, it has been proposed to incorporate triplet quenchers in organic thin films, such as oxygen,^{[ 15 , 16 ]} Cyclooctatetraene,^{[ 20 ]} or anthracene derivatives^{[ 19 ]} . However, as suggested by Schols et al.,^{[ 20 ]} The requirements for triplet quenchers are low triplet energy, short triplet lifetime, and the large difference between singlet and triplet energies, making it difficult to find a suitable triplet quencher that satisfies these conditions without hindering lasing agent. Rabe et al. demonstrated that in the absence of a triplet quencher, the 6,6'-(2,2'-octyloxy-1,1'-binaphthyl) spacer containing 12% (BN-PFO) Pseudo-cw operation at a repetition rate of 5 MHz in poly(9,9-dioctylfluorene) derivatives of radicals.^{[ 9 ]} This high repetition rate can be obtained due to less spectral overlap between emission and triplet absorption in BN-PFO.^{[ 10 ]} Therefore, the development of organic laser dyes with less spectral overlap between excited-state absorption and emission is crucial to realize cw and quasi-cw lasers with low threshold. In the group we have continuously studied the optical and amplified spontaneous emission (ASE) properties of many organic materials with the aim of realizing electrically pumped organic laser diodes.^{[ twenty one − 27 ]} Among them, 4,4'-double [(N - carbazole) styryl] biphenyl (BSBCz) is one of the most promising candidates because the host material 4,4'-bis(N Vacuum-deposited thin films of -carbazolyl)-1,1'-biphenyl (CBP) (the chemical structure of which is shown in Figure 1a) have excellent optical and ASE properties, such as a high photoluminescence quantum yield close to 100% ( Φ_PL ) and a short PL lifetime of about 1.0 ns (τ_PL ), yielding about 10⁹ the s^{− 1} The huge radiation decay constant (k_r ) and about 0.3 μJ cm^{− 2} The low ASE threshold energy.^[23,26] In this paper, we report quasi-cw surface-emitting lasers in a dispersed feedback (DFB) device based on this BSBCz:CBP blend film. In this laser setup, we obtain the highest repetition rate (up to 8 MHz) and the lowest threshold (about 0.25 μJ cm^{− 2} ). The incorporation of the triplet quencher was not necessary in our blended film due to its high Φ_PL And there is no significant spectral overlap between the emission and triplet absorption of BSBCz.^{[ twenty four ]} In the DFB structure, laser oscillation occurs when the following Bragg conditions are satisfied:mλ _Bragg = 2no _eff Λ ,inm is the diffraction order,lambda _Bragg is the Bragg wavelength,no _eff is the effective refractive index of the gain medium andΛ is the period of the grating.^{[ 28 , 29 ]} When considering the second-order mode (m = 2), use the one reported for BSBCZno _eff andlambda _Bragg Calculate the grating period asΛ = 280nm.^{[ twenty one , twenty two ]} haveΛ = The 280 nm grating provides the surface emitting laser in a direction perpendicular to the plane of the substrate as shown in Figure 1b. Although second-order gratings generally yield higher lasing thresholds compared to first-order gratings, surface-emitting lasers using second-order gratings are suitable for fabricating electrically pumped organic lasers with OLED structures exhibiting the same surface emission. diode.^{[ 30 , 31 ]} Direct engraving of these gratings down to 5×5 mm using electron beam lithography and reactive ion etching² area of the SiO2 surface (Fig. 1c). Figures 1d and 1e show SEM images of representative gratings fabricated in this study. We obtained from SEM imagesΛ = 280±2 nm andd = 70±5 nm grating depth, which fits our specifications perfectly. A 6 wt% BSBCz:CBP blend film or BSBCz pure film with a thickness of 200 nm was prepared by vacuum deposition on the grating to fabricate the laser device. First, we examined the surface emitting laser properties of our DFB system under excitation with 0.8 ns wide pulses at 20 Hz from a nitrogen laser. This excitation light with a wavelength of 337 nm is mainly absorbed by the CBP in the blended film. However, the large spectral overlap between CBP emission and BSBCz absorption guarantees efficient Förster-type energy transfer between the two molecules (Fig. 1f).^{[ 26 ]} Therefore, we did not observe any emission from CBP even under high excitation. Figures 2a and 2b show the emission spectra measured from the laser setup ((a) BSBCz:CBP film and (b) pure BSBCz film) at different excitation intensities. Both devices exhibit lasing emission with extremely narrow peaks for certain excitation light intensities. We confirmed the absence of surface emitting lasers from areas on the same substrate without gratings. Due to stimulated emission,^{[ 32 − 35 ]} In our laser device, it is found that τ_PL and full width at half maximum (FWHM) at E_{the th} The significant decrease at high excitation energies in λ (Fig. 2a and Fig. 2b), indicates that our optical grid is suitable for extracting light as surface emission from waveguide films. We observed a Bragg dip at about 478 nm for the blended film and a Bragg dip at 474 nm for the pure film in the emission spectra measured at low excitation intensities (Fig. 2a and inset of Fig. 2b). Bragg dips are caused by gratings suppressing the propagation of waveguided light, and can be envisaged as photonic stopbands for waveguide modes.^{[ 36 ]} Lasing occurs at the short wavelength edge of the Bragg dip (477 nm for blended films and 473 nm for pure films). The difference in the location of the Bragg dips is likely due to the different refractive indices used for the blended and pure films. The emission intensity increases linearly as the excitation intensity increases, and then begins to amplify for lasing as the FWHM decreases to <0.30 nm for blended films and <0.40 nm for pure films (see Figure 2c and Fig. 2d). Threshold energy of the laser measured from the intersection of two straight lines fitted to the emission intensity (E. _{the th} ) for the blended film isE. _{the th} = 0.22 μJ cm^{− 2} and for a pure film isE. _{the th} = 0.66 μJ cm^{− 2} , which corresponds to 275 W cm^{− 2} and 825 W cm^{− 2} The power density. Due to the excellent quality of our gratings, these values are lower than their 375 W cm without gratings^{− 2} and 1625 W cm^{− 2} The ASE threshold power density.^{[ twenty three , 26 ]} obtainedE. _{the th} This is the lowest value ever reported in all quasi-cw organic thin film lasers. Due to quenching of the suppressed concentration, the concentration in the blended film is lower than that in the pure filmE. _{the th} is attributed to the higher Φ of the blended film (98%) than the pure film (76%)_PL .^{[ 36 ]} Generally speaking,E. _{the th} and laser gain and Φ_PL Inversely proportional.^{[ 37 , 38 ]} Our device was operated in quasi-cw mode using optical pulses from a Ti-sapphire laser with a wavelength of 365 nm and a width of 10 ps. Figure 3 shows the striped camera image of laser oscillations and the corresponding temporal variation of laser intensity in BSBCz:CBP blend films at the laser wavelength. The excitation light intensity was fixed at about 0.44 μJ cm^{− 2} , its ratioE. _{the th} About twice as high. Laser oscillations were observed at 100 μs intervals at a repetition rate of 0.01 MHz. Decrease the time interval between laser oscillations at higher repetition rates. Neighboring laser oscillations occur continuously at 8 MHz over a broad timescale of 500 μs (Figs. 3a and 3b); however, even at 8 MHz, 125 Individual laser oscillations at ns intervals (Fig. 3c). We confirm that similar quasi-cw operation is possible for pure thin films of BSBCz. The emission intensity of both laser devices with blended and pure films remained almost constant up to 8 MHz, as shown in FIG. 3 . This maximum repetition rate is the highest ever reported and is attributed to the small absorption loss and emission quenching caused by triplet exciton formation. BSBCzΦ _PL Extremely high, thereby minimizing the generation of triplet excitons via intersystem crossing, especially for blended thin films. Furthermore, the spectral overlap between emission and triplet absorption is negligible, reducing the possibility of collisions between singlet and triplet excitons. When operating the laser device at 80 MHz (the highest frequency possible for our equipment), the emission intensity decreased rapidly and it was not possible to estimate a clear laser threshold, probably due to rapid material degradation. Furthermore, the FWHMs of the emission peaks observed at 80 MHz are about twice those of the emission peaks at lower frequencies. At this stage, we're not sure if it's lasering or not. Figure 4a shows a graph of laser threshold as a function of repetition rate for blended and pure films. Interestingly, the lasing threshold is almost independent of the repetition rate of the blended films due to negligible absorption loss and emission quenching. However, for pure thin films, a progressively increasing threshold is observed with increasing repetition rate. We do not know the exact reason for the gradual increase in threshold value, and thus further research is needed to clarify this observation. We investigated the operational stability of laser oscillations when operating the device continuously at 8 MHz (Fig. 4b). The emission intensity gradually decreases with time. The change was irreversible, indicating photodegradation of the material. The lifetime until the emission intensity drops to 90% of the initial value is 900 s for the blended film, which is longer than 480 s for the pure film. Due to the higher threshold, stronger excitation light is required to achieve lasing in pure films compared to blended films. Therefore, photodegradation can be expected to be faster in pure films. The lowering of the threshold is crucial for the containment of photodegradation. In summary, a DFB laser device combining a BSBCz:CBP blend film as the gain medium with a second-order grating was fabricated and evaluated. We self-calibrated the device under cw operation to obtain excellent surface emitting laser, where emission intensity and laser threshold are independent of repetition rate. For our laser device, the maximum repetition rate is 8 MHz, the highest ever reported, and the laser threshold is about 0.25 μJ cm^{− 2} , which is the lowest laser threshold value ever reported. Due to the negligible accumulation of triplet excitons and the small spectral overlap between emission and triplet absorption, triplet quenchers, commonly used in the manufacture of organic thin film lasers, are not necessary in our device. Therefore, we consider BSBCz to be the most promising candidate for the first realization of electrically pumped organic laser diodes in terms of optical properties. However, electrical properties such as charge carrier mobility, charge carrier trapping cross section, etc. are also extremely important and will require further research and enhancement for the realization of electrically pumped organic lasers.Experimental part The silicon substrate covered with a thermally grown silicon dioxide layer with a thickness of 1 μm was cleaned by ultrasonic treatment using neutral detergent, pure water, acetone and isopropanol, followed by UV ozone treatment. The silica surface was treated with hexamethyldisilazane (HMDS) by spin coating at 4000 rpm for 15 s. A resist layer with a thickness of about 70 nm was spin-coated on the substrate from a ZEP520A-7 solution (ZEON Co.) at 4000 rpm for 30 s and baked at 180° C. for 240 s. Use a cm with 0.1 nC^{− 2} A dose-optimized JBX-5500SC system (JEOL) was used for electron beam lithography to draw the grating pattern on the resist layer. After electron beam irradiation, the pattern was developed in a developer solution (ZED-N50, ZEON Co.) at room temperature. The patterned resist layer was used as an etch mask while using the EIS-200ERT etch system (ELIONIX) with CHF₃ Plasma etches the substrate. To completely remove the resist layer from the substrate, use the FA-1EA Etching System (SAMCO) with O₂ Plasma etches the substrate. The grating formed on the silicon dioxide surface was observed by scanning electron microscopy (SU8000, Hitachi). To complete the laser device, by 4.0×10^{− 4} Thermal evaporation under the pressure of Pa in 0.1 nm s^{− 1} to 0.2 nm s^{− 1} The total evaporation rate of 200 nm thick 6 wt% BSBCz:CBP blend film and BSBCz pure film were prepared on the grating. For laser operation, the pulsed excitation light from a nitrogen laser (USHO, KEN-2020) is concentrated on the 6×10^{− 3} cm² area. The excitation wavelength is 337 nm, the pulse width is 0.8 ns, and the repetition rate is 20 Hz. The excitation light is incident on the device at approximately 20° relative to the normal to the plane of the device. The emitted light perpendicular to the surface of the device was collected using an optical fiber connected to a multi-channel spectrometer (PMA-50, Hamamatsu Photonics), which was placed at a distance of 3 cm from the device. Use a set of neutral density filters to control the excitation intensity. For quasi-cw operation, a mode-locked frequency-doubled Ti-sapphire laser (Millennia Prime, Spectra physics) was used to generate excitation with an excitation wavelength of 365 nm, a pulse width of 10 ps, and a repetition rate ranging from 0.01 MHz to 8 MHz Light. The excitation light is concentrated on the 1.9×10 of the device through the lens and the slit^{− 4} cm² and the emitted light was collected using a streak scope (C10627, Hamamatsu Photonics) with a time resolution of 15 ps connected to a digital camera (C9300, Hamamatsu Photonics). 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Bubble a liquid gain medium with oxygen or nitrogen to study the effect of triplet quenchers such as molecular oxygen on the quasi-CW laser properties of organic semiconductor lasers. The oxidized laser device exhibits 2 μJ cm^{- 2} The low threshold value of , which is lower than the threshold value measured in the nitriding device and is independent of the repetition rate in the range between 0.01 MHz and 4 MHz. Since the demonstration of the first optically pumped organic solid-state semiconductor laser in 1996,^{1 , 2} Organic lasers have been the subject of intensive research mainly due to several attractive features of organic semiconducting materials, such as their broad absorption and emission spectra, and their high optical gain coefficients.^{3 , 4} The performance of organic solid-state lasers has been greatly improved during the past two decades, and applications are now emerging including the development of integrated light sources for spectroscopic analysis and vapor chemical sensors.⁵ Although pulsed inorganic light-emitting diodes can now be used to optically pump organic solid-state lasers,⁶ But further breakthroughs are still needed to demonstrate optically pumped organic semiconductor lasers operating in the continuous wave (cw) regime and eventually realize optically pumped organic laser diodes. It is well established that generation of long-lived triplet excitons via intersystem crossing can lead to high photon and singlet losses that prevent lasing in the cw optically pumped state.^{7 - 12} To address this critical issue, the incorporation of triplet quenchers into organic semiconductor gain media has been proposed. Zhang et al. In the doping of 4-(dicyanomethylene)-2-methyl-6-pyrrolidinyl-9-enyl-4H-pyran (DCM2) ginseng (8-hydrixyquinoiline) aluminum (Alq₃ ) using anthracene derivatives as triplet quenchers and can extend the laser duration of their distributed feedback (DFB) organic devices to nearly 100 μs.⁸ Meanwhile, some other studies have demonstrated that triplet loss in optically pumped organic semiconductor lasers can be reduced by using oxygen or cyclooctatetraene (COT) as a triplet quencher.^{9 - 11} Although the use of triplet quenchers to develop true cw organic solid-state laser technology is very promising, it should be mentioned that other approaches have been proposed to achieve this goal. Recently, based on 4,4'-bis(N-carbazolyl)-1,1'-biphenyl doped with 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) Quasi-cw lasers with repetition rates up to 8 MHz have been demonstrated in benzene (CBP)-hosted organic DFB lasers.¹³ This achievement is explained by the negligible overlap between the lasing emission and triplet absorption spectra of BSBCz and the photoluminescence quantum yield of nearly 100% of the material, which results in triplet The state of production is extremely weak. Another approach to realize high-power cw organic solid-state dye lasers is based on extremely fast rotation of the device during its operation, but the long-term power output stability of these devices appears to be limited for practical applications.¹⁴ In this study, we report on the fabrication of organic semiconductor DFB lasers operating in the quasi-cw state using solvent-free liquid organic semiconductor materials as laser gain media.^{15 - twenty three} The laser material is composed of 9-(2-ethylhexyl)carbazole (EHCz) doped with heptyl derivatives¹⁷ composition.^{twenty four} The chemical structures of these molecules are shown in Figure 5a. The photoluminescence quantum yield (PLQY) of 85% and its 0.4 μJ cm^{- 2} The choice of this blend was driven by the low amplified spontaneous emission (ASE) threshold.^{twenty two} In this context, we here examine the effect of oxidation on the quasi-cw DFB laser properties of EHCz:septine blends. The results provide clear evidence that the use of triplet quenchers such as molecular oxygen is very promising for the future realization of optically pumped cw organic semiconductor lasers. According to previously published literature²⁵ The method in the synthesis of seven tertiary derivatives, while purchasing liquid carbazole, EHCz (Sigma-Aldrich) and used without further purification. EHCz, which is liquid at room temperature and exhibits a glass transition temperature well below 0°C,¹⁷ It was mixed with seven tertiary in chloroform solution. The EHCz:Seventillium (90:10 wt.%) blend solution was then bubbled by oxygen or nitrogen for about 20 minutes. Gas was incorporated into the solution by using a needle with an inner diameter of 0.7 mm and at a pressure of about 0.02 MPa. The blend was then used as a gain medium in a laser device after complete evaporation of the solvent. The device structure of liquid DFB laser is schematically shown in Fig. 5b. To fabricate these devices, ultraviolet (UV) curable polyurethane acrylate (PUA) mixtures were synthesized following previously reported methods.²⁶ Rippled polymeric DFB patterns were easily fabricated on polyethylene terephthalate (PET) substrates by replicating silicon grating masters with PUA mixtures.²⁷ Grating period for the desired laser wavelength λΛ Prague conditions must be metΛ =mλ/(2n_eff ), where m is the order number and n_eff is the effective index of refraction for the guided mode. To achieve low-threshold laser operation, a first-order feedback corresponding to m = 1 is chosen, which results from the laser emission from the edge of the device. It is worth noting that the refractive indices of the PUA film and the EHCz blend are about 1.54 and 1.7, respectively, implying a relative refractive index difference of 0.16.^{twenty two} As shown in Figure 5c, the patterned corrugated structure on the PUA layer consisted of a 1D grating with a period of 140 nm and a height of 100 nm. This grating period was chosen for first-order DFB laser operation with an emission wavelength of about 450 nm, based on the Bragg formula and the emission spectrum of the blue-emitting seven-stemme derivatives. The corrugated PUA layer was then covered with a fused silica substrate, and the gap distance between the PUA replica and the covering was fixed using silica particles with a diameter of 1 μm. The empty interstitial space is then filled with liquid gain medium via capillary action. To study its quasi-cw laser properties, a Ti-sapphire laser system (Millennia Prime, Spectra Physics) delivering optical pulses at 365 nm with a pulse width of 10 ps was used to optically nitride and oxidize the EHCz: Heptospermum DFB laser. The repetition rate of optical excitation was varied in the range of 0.01 MHz to 4 MHz. The spot area of the laser pump beam concentrated on the device is 1.9×10^{- 4} cm² . Emissions were detected from the edge of the device using a Hamamatsu strip eye (C10627) connected to a Hamamatsu digital video camera (C9300). Septelium derivatives were previously used in solution-processed fluorescent organic light emitting diodes (OLEDs) with external quantum efficiencies as high as 5.3%.²⁸ Such good electroluminescent performance can be achieved due to the horizontal orientation of the heptane emitter in the 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) host. In another study, heptera molecules were also incorporated into EHCz hosts in order to demonstrate a solvent-free liquid organic second-order DFB laser operating in the blue region of the visible spectrum.^{twenty two} For this purpose, the device was optically pumped using a pulsed nitrogen laser (λ = 337 nm, pulse duration 800 ps and repetition rate 8 Hz) and the laser output emission was detected in a direction perpendicular to the surface. Here, we use the same liquid composite to fabricate an edge-emitting first-order DFB laser. As shown in Figures 5d and 5e, the blue laser emissions detected from the edges of the nitrided and oxidized liquid DFB lasers have peak wavelengths of 450 nm and 449 nm, respectively. The very small difference between the laser wavelengths of the two devices is presumably due to the small variation in the thickness of the organic liquid layer.²⁹ Figures 6a and 6b show frame camera images for laser emission at several repetition rates for two nitrided and oxidized solvent-free liquid organic DFB lasers. For these measurements, the excitation intensity was kept constant at 2.5 μJ cm^{- 2} value. When the laser pulses emitted from the DFB laser are clearly observable in the 100 μs time-scale window, the time interval between pulses gradually decreases with increasing repetition rate. For the highest repetition rates of 1 MHz and 4 MHz, the DFB laser output emissions in Fig. 6c and Fig. 6d appear to emit continuously over this time frame, providing evidence that both nitridated and oxidized devices are in the quasi-cw state Operate properly. It is worth noting, however, that the output intensity of the oxidized devices in the quasi-cw state, especially at 4 MHz, was consistently found to be significantly higher than that of the nitrided devices.³⁰ The laser output intensity and the full width at half maximum (FWHM) of the emission spectrum were plotted against the excitation intensity at different repetition rates in the nitrided and oxidized solvent-free liquid organic DFB lasers (Fig. 7 and Fig. 8).³⁰ The FWHM of the emission peak in both samples was found to decrease to 1.8 nm at high excitation density, which was attributed to the amplification by the stimulated emission. This linewidth is higher than the resolution of a spectrometer at 0.7 nm. Observing the curve showing the output intensity versus the excitation intensity, the sudden change in slope efficiency is directly related to the laser threshold.^{29 , 31 - 34} Using this information, the laser threshold was then determined based on the repetition rate in both devices. The results in Fig. 9a demonstrate that the laser threshold is lower and almost the same as that with 2 μJ cm^{- 2} The value of is independent of the repetition rate in the oxidized sample. Interestingly, it was found that the lasing threshold in nitrided samples increased gradually from 2.8 μJ cm as the repetition rate of optical picosecond pulse excitation increased from 0.01 MHz to 4 MHz.^{- 2} increased to 4.4 μJ cm^{- 2} . A non-negligible overlap was observed between the triplet-triplet absorption spectrum of the septemme molecule in chloroform solution and the representative laser spectrum of the gain material (FIG. 10).³⁰ Indeed, previous work reported that the stimulated emission cross section in Septella is seven times larger than the triplet absorption cross section at ASE/laser wavelengths.¹⁰ It is noteworthy that the triplet-triplet absorption completely disappears in the oxidized solution due to the presence of molecular oxygen which acts as a triplet quencher. To provide additional evidence that molecular oxygen can efficiently quench triplet states in heptaploline-based laser gain media, we next examine mutual destruction of singlet-triplet excitons in liquid blend materials bubbled with oxygen or nitrogen (STA) Quenching of singlet excitons. For this purpose, the nitrided and oxidized gain material is sandwiched between two planar fused silica substrates. 0.5 kW cm by 325 nm light pulses (with pulse durations varying from 50 μs to 800 μs)^{- 2} The sample was irradiated with an excitation density of , and we monitored the time evolution of the photoluminescence intensity.^{8 - 10} The transient curves in the nitrided samples show a dramatic decrease in emission intensity of almost 60% after 300 μs after the onset of optical pumping before reaching its steady state ( FIG. 11 ).³⁰ These data demonstrate that singlet excitons are quenched by STA in nitrided liquid materials.^{8 - 10} In contrast, the oxidized liquid gain medium did not exhibit such quenching, and additionally, did not exhibit any sign of degradation under high intensity cw irradiation of 800 μs. This and previous studies¹⁰ The results reported in , are consistent and provide clear evidence that molecular oxygen can in fact be used to quench the triplet state without affecting the singlet state in materials based on heptame. Suppression of singlet quenching by STA in oxidized samples is also consistent with the fact that the intensity of DFB lasing emission appears to be stronger in oxidized devices than in nitrided devices. With these considerations, the highest threshold and the repetition rate dependence of this threshold in nitrided DFB laser devices can be attributed to the generation and accumulation of long-lived triplet excitons in the gain medium, which Additional losses associated with triplet absorption and singlet-triplet exciton mutual destruction result. It should be highlighted that the liquid blend exhibited a high PLQY of 85% and a low ASE/laser threshold. In addition, the crossover yield between systems is generally small (about 3%) in oligo- and poly- terfenene derivatives.³⁵ In this case, it is quite plausible that the concentration of triplet states generated via intersystem crossing under optical pumping is kept low enough in the nitrided heptene-based gain material to observe for repetition rates up to 4 MHz Laser in quasi-cw state. Importantly, the fact that the lasing threshold becomes lower in oxidized DFB devices independent of repetition rate can be directly explained by the presence of molecular oxygen acting as a triplet quencher. The performance of quasi-cw laser emission was also evaluated by monitoring the time evolution of the output intensity from the edge of the liquid layer of the laser threshold for two nitrided and oxidized DFB lasers at repetition rates above 1 MHz. Photostability. A characteristic photostability time constant was estimated by measuring the duration associated with a 10% decrease in output intensity from the initial value. As shown in Figure 9b, the time constants for the nitrided and oxidized devices were found to be 4 minutes and 5 minutes, respectively. This decrease over time in the output laser intensity is presumably due to bleaching of the heptene molecules. This photodegradation problem can of course be solved by using microfluidic circuits for true quasi-cw solvent-free liquid organic semiconductor laser technology.^{twenty two} Interestingly, despite the formation of highly chemically reactive oxygen singlets upon quenching of triplet excitons, the presence of oxygen did not lead to faster photodegradation of liquid devices.³⁶ It was obtained showing that the photoluminescence intensity from the oxidized sample was in the range of 0.5 kW cm^{- 2} This is well supported by the fact that cw optical pumping at high excitation densities remains almost constant after 800 μs.³⁰ In conclusion, we demonstrate that the use of oxygen as a triplet quencher is a promising avenue for the development of continuous wave organic semiconductor laser technology. The gain medium used in our first-order organic DFB laser is based on a solvent-free liquid carbazole host doped with a blue-fluorescing ascetine derivative. 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Here we report a low-threshold surface-emitting organic dispersive regenerative laser operating in the quasi-CW regime at 80 MHz and under 30 ms of CW optical excitation. This outstanding performance is achieved using an organic semiconductor film with high optical gain, high photoluminescence quantum yield, and no interference at laser wavelengths combined with a hybrid order dispersive feedback grating to achieve a low laser threshold. Triplet absorption loss. Simple encapsulation techniques greatly reduce laser-induced thermal degradation and contain the erosion of the gain medium that otherwise occurs under intense continuous wave optical excitation. In conclusion, this study provides evidence that the development of true CW organic semiconductor laser technology is possible through engineering of the gain medium and device architecture.introduction Due to the ability of organic semiconductor materials to emit, modulate and detect light, organic semiconductor materials are generally considered to be very suitable for photonic applications (1 ). In particular, due to its outstanding characteristics in terms of low-cost fabrication, ease of processing, chemical versatility, mechanical flexibility, and wavelength tunability across the entire visible range, considerable research has been carried out over the past two decades work to use these organic semiconductor materials in optically pumped solid-state laser sources (2 -6 ). Since the first demonstration of optically pumped organic semiconductor lasers (OSL) (2 ), the performance of which has been greatly improved due to significant advances in both high-gain organic semiconductor materials and device design (7 - 15 ). Due to recent developments in low-threshold decentralized feedback (DFB) OSLs, it is demonstrated that direct optical pumping of electrically driven nanosecond-pulsed phosphors provides a path towards new compact and low-cost visible laser technologies. way(12 , 13 ). Applications based on these OSLs are emerging, including the development of spectroscopic tools, data communication devices, medical diagnostic equipment, and chemical sensors (16 , 20 ). Nonetheless, OSLs are optically pumped by pulsed optical excitation (with pulse width typically varying in the range of 100 fs to 10 ns) and driven at repetition rates (f) in the range of 10 Hz to 10 kHz. In this context, further breakthroughs are still needed to demonstrate optically pumped OSLs operating in the continuous wave (CW) regime and eventually realize electrically pumped organic laser diodes (twenty one , twenty two ). Operating the OSL in the CW state has proven challenging (twenty three , twenty four ). Thermal degradation of organic gain media under intense long-pulse optical pumping presents a serious problem for long-term laser operation (25 ). Another important issue to overcome concerns the losses caused by long-lived triplet excitons generated via intersystem crossing (26 - 29 ). When organic thin films are optically pumped in the long-pulse regime, accumulation of triplet excitons typically occurs, resulting in increased absorption at laser wavelengths due to triplet absorption (TA) and increased absorption due to singlet-triplet Quenching of singlet excitons by mutual exciton destruction (STA). To overcome these obstacles, it has been proposed to incorporate triplet quenchers, such as oxygen (30 , 31 ), cyclooctatetraene (32 ) and anthracene derivatives (33 ). Another approach to substantially reduce triplet loss is based on the use of emitters that exhibit high photoluminescence quantum yields (PLQY) and no spectral overlap between the absorption band of the triplet excited state and the emission band of the singlet excited state (34 - 36 ). Two approaches to suppress the triplet loss of OSL have been successfully used to improve device performance in the quasi-CW (qCW) state (31 , 35 ). Meanwhile, a CW laser duration close to 100 μs can be achieved in an OSL containing an anthracene derivative as a triplet quencher (33 ). In this paper, we propose a modified DFB OSL architecture enabling quasi-CW (qCW) lasers (at extremely high repetition rates of 80 MHz) and CW surface-emitting lasers with outstanding and unprecedented performance. These results represent a major development in the field of organic photonics and open new perspectives towards the development of reliable and cost-effective organic-based CW solid-state laser technologies.result In this study, the fabricated surface-emitting OSL used the 4,4'-bis[(N - Carbazole) styryl] biphenyl (BSBCz) as emitter (34 ). Incorporation of triplet quenchers into BSBCz thin films is not necessary due to the extremely weak generation of triplet states via intersystem crossing and negligible triplet absorption at laser wavelengths in this material (35 ). The fabrication method and structure of the organic semiconductor DFB laser fabricated in this study are schematically shown in Fig. 12 and Fig. 13A, respectively. To achieve a low lasing threshold with lasing emission in the direction perpendicular to the substrate plane, we designed a hybrid-order DFB grating architecture with a second-order Bragg scattering region surrounded by a first-order scattering region causing strong feedback, thus providing Efficient vertical extraction of laser radiation (8 ). In the DFB structure, laser oscillation occurs when the following Bragg conditions are satisfied:mλ _Bragg =2no _eff Λ (5 ),inm is the diffraction order,lambda _Bragg is the Bragg wavelength,no _eff is the effective refractive index of the gain medium andΛ is the period of the grating. Using the reported for BSBCzno _eff value andlambda _Bragg value(37 - 39 ), mixed order (m =1, 2) The grating periods of the DFB laser device are calculated to be 140 nm and 280 nm respectively. Direct engraving of these gratings down to 5×5 mm using electron beam lithography and reactive ion etching² area of the silicon dioxide surface. It should be noted that the optical simulation and experimental data reported in Figures 16-17 and Tables S1-S3 (see Section A, Supplementary Material) were considered to select parameters for resonator design. As shown by the scanning electron microscopy (SEM) images in Figures 13B-13C, the DFB gratings fabricated in this work have grating periods of 140±5 nm and 280±5 nm and gratings of about 65±5 nm Depth, it meets our standards. The lengths of each of the first-order and second-order DFB gratings are about 15.12 µm and 10.08 µm, respectively. BSBCz pure and BSBCz:CBP (6:94 wt.% and 20:80 wt.%) blended films were prepared by vacuum deposition on top of the gratings with a thickness of 200 nm. As shown in Figures 13D-13E, the surface morphology of the organic layer presents a grating structure with a surface modulation depth of 20 nm to 30 nm. To greatly improve the efficiency and stability of the DFB laser operating in the qCW regime and the long-pulse regime, the device was then encapsulated in a nitrogen-filled glove box (40). For this purpose, 0.05 ml of CYTOP (a chemically stable, optically transparent fluoropolymer with a refractive index of about 1.35) was spin-coated directly on top of the organic layer, and then the polymer film was covered by a transparent sapphire cap to To seal an organic laser device, the sapphire cap was chosen for its good thermal conductivity at the BSBCz laser wavelength (TC about 25 W m at 300 K^{- 1} K^{- 1} ) and good transparency. CYTOP films typically have a thickness of about 2 µm and were found not to affect the photophysical properties of BSBCz films (Figure 18). The use of pure thin films of BSBCz or blends of BSBCz:CBP (6:94 wt.%) was first examined under pulsed optical pumping using a nitrogen laser delivering 800 ps pulses at a repetition rate of 20 Hz and a wavelength of 337 nm Lasing properties of encapsulated mixed-order DFB devices with thin films as gain medium (see Section B and Figure 19, Supplementary Material). In the case of CBP blended films, the excitation light is mainly absorbed by the CBP host, but the large spectral overlap between the CBP emission and the BSBCz absorption ensures efficient Förster-type energy transfer from the host molecule to the guest molecule (39 ). This was confirmed by the absence of CBP emission under 337 nm light excitation. Based on the results shown in Figure 19, it was found that the pure thin-film device and the blended thin-film device exhibited 0.22 µJ cm^{− 2} and 0.09 µJ cm^{− 2} low laser threshold. In both cases, these values are lower than those previously reported for Amplified Spontaneous Emission (ASE) in BSBCz:CBP blends (0.30 μJ cm^{− 2} )(39) and second-order DFB laser (0.22 μJ cm^{− 2} ) (35) reported cut-off value, (35 −39 ) supports the possibility of hybrid-order gratings for high-efficiency organic solid-state lasers (8 ). Importantly, it was found that device encapsulation in this pulsed optically pumped state did not change the threshold and laser wavelength of mixed-order DFB lasers.organic semiconductor DFB laser accuracy CW laser Various BSBCz and BSBCz:CBP (6:94 wt.%) with different resonator structures were studied for optical pumping in the qCW state using optical pulses from a Ti-sapphire laser with a wavelength of 365 nm and a width of 10 ps Laser properties of DFB devices. Figures 14A-14C show framed camera images of laser oscillations above threshold and the corresponding changes in emission intensity at different repetition rates in a representative encapsulated blend mixed-stage DFB device. The excitation light intensity is fixed at about 0.5 µJ cm^{− 2} . When increasing the repetition rate of optical excitation from 10 kHz to 80 MHz, the time interval between laser oscillations gradually decreased from 100 µs to 12.5 ns. For the highest repetition rate (>1 MHz), the DFB laser output emissions appear to be continuous in the 500 µs window, indicating that even at the highest repetition rate of 80 MHz, the device is operating properly in the qCW regime. The possibility of operating a DFB device at these high repetition rates is clearly associated with less TA loss and STA quenching from negligible triplet exciton formation in BSBCz:CBP blends (35 ). Similar experiments were performed with non-encapsulated hybrid stage devices and second-order DFB devices based on BSBCz pure or blended films. For each device, the laser output intensity obtained at several repetition rates was measured according to the excitation intensity to determine the laser threshold, and for a representative encapsulation blend mixing order at repetition rates of 10 kHz and 80 MHz The results for the DFB device are shown in FIG. 20 . The repetition rate dependence of laser threshold in different devices is summarized in Figure 14D. The lasing threshold in 6 wt.% doped DFB lasers is essentially due to the PLQY close to 100% and the containment of concentration quenching in this gain medium (as compared to the PLQY of 76% in BSBCz pure films). value(E. _{the th} ) is always lower (36 ). The results also show that the lowest threshold is obtained with the mixed-order DFB resonator structure. It is noteworthy that the laser threshold for all devices increased only very slightly when the repetition rate was increased from 10 kHz to 8 MHz. Due to the absence of significant triplet accumulation in the BSBCz system (35 ), we attribute the small increase in the threshold value of repetition rate to slight degradation of the device under high-intensity qCW irradiation (see Figure 21). Interestingly, the encapsulated blend mixed-order DFB laser exhibited the lowest threshold (from 0.06 µJ cm at 10 kHz² to 0.25 µJ cm at 80 MHz² variation) and is the only device that operates properly at 80 MHz. When other devices are optically pumped at 80 MHz, the emission intensity decreases very rapidly and the FWHM value of the emission spectrum detected with a frame camera is usually large, about 7 nm to 8 nm, before the rapid degradation of the organic film (Figure 22). This indicates that encapsulation of DFB devices is necessary to significantly reduce degradation and that laser ablation of organic thin films presumably occurs under high intensity 80 MHz optical excitation. This reduction in device degradation due to encapsulation is presumably responsible for the reduction in lasing threshold observed in Figure 14D. The operational stability of different doped DFB devices was investigated under qCW optical pumping at 8 MHz. Similar experiments were also performed using encapsulated mixed-order DFB lasers at a repetition rate of 80 MHz. For each device, the time evolution of different DFB laser output intensities was monitored for 20 minutes using pump intensities greater than 1.5 times the laser threshold (FIG. 23). These results show that operational stability is improved when the laser threshold is reduced through the choice of grating structure and encapsulation. Higher pump intensities are required to achieve lasing in devices with higher thresholds, which results in faster laser-induced thermal degradation. More importantly, although none of the unencapsulated DFB devices operated well under qCW optical pumping at 80 MHz, the emission output intensity from the encapsulated organic laser decreased to only its 96% of the initial value. This excellent operational stability underscores the critical role of encapsulation on the performance of organic semiconductor DFB lasers operating in the qCW state.organic semiconductor DFB truth in a laser CW laser The amplified spontaneous emission (ASE) properties of 200 nm thick BSBCz:CBP (20:80wt.%) films were studied using the variable strip length method to gain insight into the optical gain and loss coefficients under long-pulse light irradiation. As shown in Figure 24 (see Table S4 and Section C in the Supplementary Material), thin films optically pumped with 50 μs long pulses at 405 nm exhibit^{− 2} 40 cm of pump strength^{− 1} The high net gain factor and 3 cm^{− 1} loss factor. This clearly supports our idea that BSBCz are excellent candidates for organic semiconductor lasers operating under long-pulse optical excitation. The laser properties of the DFB device in CW mode were then investigated using an inorganic laser diode emitting at 405 nm. Since the absorption of CBP is negligible at this excitation wavelength (30 ), the concentration of BSBCz in the blend was increased to 20 wt.% to improve the harvest of laser diode pump emission. The PLQY of this 20 wt.% blend was measured to be about 86%. Figure 15A shows the frame camera integrated within 100 pulses of an encapsulated 20 wt.% blend mixed-order DFB laser shot for a CW excitation pulse width of 800 µs and 30 ms, respectively at 200 W cm^{− 2} and 2.0 kW cm^{− 2} measured at the pump intensity. The corresponding emission spectra in Figure 25 and the picture in Figure 15B provide additional evidence that encapsulated DFB lasers operate properly in the long pulse regime, with laser durations that can be significantly extended beyond 30 ms. Additional data in Figure 26 provide additional evidence of lasing under 30 ms long pulsed light excitation. As shown in Figure 27, when the number of consecutive 30 ms long excitation pulses was increased from 10 to 500, the DFB laser emission output intensity decreased, presumably due to the thermal degradation of the gain medium under this intense irradiation. Although the encapsulation of devices between high thermal conductivity silicon and sapphire significantly improves the performance and stability of OSLs to unprecedented levels, this situation shows that the development of practical CW organic laser technology will still require further research and development in the future. Improved heat dissipation. Figure 27 also shows that quenching of singlet excitons by TA or STA did not occur in BSBCz (see Section D, Supplementary Material). The results confirm negligible overlap between the emission of BSBCz and the triplet absorption of BSBCz and the absence of deleterious triplet loss in the gain medium even under severe CW photoexcitation (35 ). To verify the requirements of the CW laser, the divergence of the emitted beam below and above the threshold and its polarization are checked. The results shown in Figures 28-29 confirm that proper laser operation occurs in the BSBCz DFB device under long pulse light irradiation. The output intensity and emission spectrum of organic DFB lasers are measured according to the excitation intensity and various long pulse durations in the range of 0.1 µs to 1000 µs in devices with different structures. An example of data obtained from a representative encapsulated blend mixing stage device is shown in FIG. 30 . The abrupt change in the slope efficiency of the laser output intensity is again used to determine the laser threshold. Figure 15C summarizes the pulse duration dependence of laser threshold measured in different devices. Similar to the trend observed in the qCW regime, incorporation of BSBCz into the CBP host, using mixed-order DFB resonator structures and encapsulation devices resulted in a substantial reduction in the lasing threshold. Encapsulated blend mixed-order organic DFB lasers exhibit the lowest lasing threshold when encapsulated mixed-order DFB devices based on BSBCz pure thin films can be properly operated in the long-pulse regime for durations longer than 100 µs Value (at 5 W cm^{− 2} to 75 W cm^{− 2} range) and is the only device that can efficiently generate laser light for a duration longer than 800 µs. To provide additional evidence for the critical role played by the choice of high TC sapphire as the capping cap on the performance of organic semiconductor lasers in the long-pulse regime, we compared doped DFB in mixed stages encapsulated with either sapphire cap or glass cap Excitation duration dependence of laser thresholds obtained in the device. Figure 31 clearly demonstrates that using a high TC cap made of sapphire results in lower thresholds and improved operational stability. The operational stability of encapsulated or unencapsulated mixed-order DFB lasers in the long-pulse regime was characterized by monitoring these devices above 200 W cm^{− 2} The laser emission output intensity of the laser threshold value varied by the number of 100 µs excitation pulses of the pump intensity. As shown in Figure 15D, in all devices, emission intensity gradually decreased over time, and this decrease was irreversible, indicative of laser-induced thermal degradation of the organic gain medium. Notably, handling stability is greatly improved by encapsulation and is clearly optimal for encapsulated blending devices. In the latter case, the laser output intensity decreased by only 3% after 500 pulses. Figure 32 shows the unencapsulated blend mixed stage DFB laser at^{− 2} Laser microscope images before and after irradiation with 100 incident pulses of the same excitation intensity. Although no sign of any laser-induced thermal degradation was observed in the encapsulated device, laser ablation occurred in the unencapsulated device with an ablation depth of about 125 nm. Greatly reducing the possibility of laser ablation by the proposed encapsulation technique is clearly critical for the future development of CW organic semiconductor laser technology. To draw conclusions on how existing devices are limited in terms of practical CW operation, thermal simulations of heat dissipation in the device were performed and reported in Figures 38-42 (see Table S4 and Section E, Supplementary Material). These results demonstrate the effect of pump pulse width and the effect of encapsulation on the thermal properties of the device. Specifically, although encapsulation has been considered an important element in this study, simulations indicate that CYTOP should be replaced by another material with better thermal conductivity in further studies.discuss Inorganic CW solid-state lasers were first demonstrated about 40 years ago (41), and development has proven to be extremely successful, especially at wavelengths in the near-infrared and ultraviolet/blue regions of the electromagnetic spectrum (42 - 45 ). Although these devices typically require cutting-edge microfabrication techniques with high vacuum and temperature conditions, it has recently been demonstrated that solution-processed inorganic quantum wells can also be used to achieve CW lasers (46 ). On the other hand, the performance of organic semiconductor lasers in the qCW and long-pulse regimes has so far remained much lower than that of inorganic semiconductors (33 , 35 ). Therefore, our demonstration of an organic semiconductor laser operating in the qCW regime at 80 MHz and still operating in the long-pulse regime after 500 consecutive pulses of 30 ms represents an important step toward the development of practical CW organic solid-state laser technology. progress. This study strongly supports the fact that organic lasing materials with high PLQY, high optical gain, and no spectral overlap between the lasing emission peak and the TA band are essential for suppressing triplet loss and achieving it when combined with mixed-order DFB gratings. A low threshold CW laser is highly desirable. The results also show that using the thermal conductivity (47 ) higher than the mutual thermal conductivity of conventional glass and fused silica caps and sapphire caps significantly improve the efficiency and stability of organic DFB lasers, but under intense CW optical pumping, organic Laser-induced thermal degradation of gain media remains the most serious problem that will need to be overcome in the near future. Therefore, considering the aforementioned methods that may be developed for improving thermal management in CW inorganic solid-state lasers, further research on greatly enhancing the operational stability of CW organic semiconductor lasers should now focus on Research and development of organic semiconductor gain media with enhanced thermal stability and focus on integrating efficient heat dissipation systems into devices (48 , 49 ). Furthermore, in addition to the discovery of better and more efficient gain materials, further optimization of resonator geometries and lasing structures should lead to lower lasing thresholds and should still represent the development of CW organic laser technology and electrically pumped An important future direction for the realization of organic laser diodes.Materials and methods Device manufacturing The silicon substrate covered with a thermally grown silicon dioxide layer of 1 μm thickness was cleaned by ultrasonic treatment using alkaline cleaner, pure water, acetone and isopropanol, followed by UV ozone treatment. The silicon dioxide surface was treated with hexamethyldisilazane (HMDS) by spin coating at 4000 rpm for 15 s and annealed at 120 °C for 120 s. A resist layer with a thickness of about 70 nm was spin-coated from a ZEP520A-7 solution (ZEON Co.) on the substrate at 4000 rpm for 30 s and baked at 180° C. for 240 s. Use a cm with 0.1 nC^{− 2} A dose-optimized JBX-5500SC system (JEOL) was used for electron beam lithography to draw the grating pattern on the resist layer. After electron beam irradiation, the pattern was developed in a developer solution (ZED-N50, ZEON Co.) at room temperature. The patterned resist layer was used as an etch mask while using the EIS-200ERT etch system (ELIONIX) with CHF₃ Plasma etches the substrate. To completely remove the resist layer from the substrate, use the FA-1EA Etching System (SAMCO) with O₂ Plasma etches the substrate. The grating formed on the silicon dioxide surface was observed using a SEM (SU8000, Hitachi). To complete the laser device, by 2.0×10^{− 4} Thermal evaporation under the pressure of Pa in 0.1 nm s^{− 1} to 0.2 nm s^{− 1} The total evaporation rate of 200 nm thick 6 wt% or 20 wt% BSBCz:CBP blend film and BSBCz pure film were prepared on the grating. Finally, 0.05 ml of CYTOP (Asahi Glass Co., Ltd., Japan) was spin-coated directly onto the DFB laser device at 1000 rpm for 30 s, sandwiched with a sapphire cap to seal the top of the laser device, and dried overnight in vacuum.Spectrum measurement In order to characterize the pulsed organic laser, the pulsed excitation light from the nitrogen laser (USHO, KEN-2020) was concentrated on the 6×10 of the device through the lens and the slit^{− 3} cm² area. The excitation wavelength is 337 nm, the pulse width is 0.8 ns, and the repetition rate is 20 Hz. The excitation light is incident on the device at approximately 20° relative to the normal to the plane of the device. The emitted light perpendicular to the device surface was collected using an optical fiber connected to a multi-channel spectrometer (PMA-50, Hamamatsu Photonics) and placed 3 cm away from the device. Use a set of neutral density filters to control the excitation intensity. For qCW operation, a mode-locked frequency-doubled Ti-sapphire laser (Millennia Prime, Spectra physics) was used to generate excitation light with an excitation wavelength of 365 nm, a pulse width of 10 ps, and a repetition rate ranging from 0.01 MHz to 80 MHz . The excitation light is concentrated on the 1.9×10 of the device through the lens and the slit^{− 4} cm² and the emitted light was collected using a frame eye (C10627, Hamamatsu Photonics) with a time resolution of 15 ps connected to a digital camera (C9300, Hamamatsu Photonics). For real CW operation, a CW laser diode (NICHIYA, NDV7375E, maximum power 1400 mW) was used to generate excitation light with an excitation wavelength of 405 nm. In these measurements, pulses were delivered using an acousto-optic modulator (AOM, Gooch & Housego) triggered by a pulse generator (WF 1974, NF Co.). The excitation light is concentrated on the 4.5×10 of the device through the lens and the slit^{− 5} cm² and the emitted light was collected using a frame eye (C7700, Hamamatsu Photonics) with a time resolution of 100 ps connected to a digital camera (C9300, Hamamatsu Photonics). Emission intensities were recorded using a photomultiplier tube (PMT) (C9525-02, Hamamatsu Photonics). Both the PMT response and the driving square wave signal were monitored on a multi-channel oscilloscope (Agilent Technologies, MSO6104A). The same illumination and detection angles were used for this measurement as previously described. The size of the excitation area was carefully checked by using a beam mapper (WimCamD-LCM, DataRay). All measurements were performed under nitrogen atmosphere to prevent any degradation caused by moisture and oxygen. Preparation containing BSBCz dissolved in CH₂ Cl₂ The solution was bubbled with argon before use. 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These properties make it a good candidate for many applications including sensing, display applications, data storage, and xerographic printing. However, only optically pumped organic lasers have been achieved so far. Much effort has been focused on reducing the energy threshold of optically pumped organic lasers by enhancing the properties of the gain medium [2], [3] and optimizing the resonant cavity [4], [5], [6]. In view of the achievement of electrically pumped organic lasers, which has not yet been achieved, more optimization is required to further reduce the energy threshold. Regarding resonators, there exist several types compatible with organic gain media, including distributed feedback (DFB) resonators [7], [8], distributed Bragg resonators (DBR) [9], microrings [10], Microdisk [11] and microsphere cavity [12]. The role of the resonator is to provide positive optical feedback in addition to the optical amplification provided by the gain medium. Laser architectures for state-of-the-art organic lasers are based on DFB resonators [5], [4], [13]. These resonators do not use conventional cavity mirrors, but instead use periodic nanostructures responsible for Bragg diffraction. DFB resonators are compact and can be easily integrated in planar organic thin films. In addition, it can provide a higher degree of spectral selectivity. The laser structure studied in this work consists of an organic thin film deposited on a 2-level DFB grating. In such gratings, light generated by the gain medium is waveguided along a high index organic film and then scattered by the periodic structure. Optical feedback occurs due to the coupling between the forward-propagating wave and the backward-propagating wave [14]. This coupling is the maximum value for a specific wavelength satisfying the following Bragg conditions:

(1) of whichm is the diffraction angle,l _Bragg is the resonant wavelength in the cavity,n _eff is the effective refractive index of the uniform waveguide, and L is the grating period. In the second order grating (m =2), the first-order diffracted light is extracted vertically from the surface of the film, while the coplanar feedback is provided by the second-order diffraction. According to the coupled mode theory, wavelengths satisfying the Bragg condition (1) are not allowed to propagate in thin films [15]. This is due to the periodic modulation of the refractive index, which leads to the appearance of a photonic stop band centered on the Bragg wavelength. Thus, inl _Bragg Below, a sudden drop in emission is observed and laser oscillations occur at a pair of wavelengths located on the edge of the stop band. In second-order gratings, the laser oscillations are only at one edge of the stop band (at the highest wavelength). At this wavelength, the threshold is lower due to lower radiative losses [16]. The resonant cavity affects the laser performance via two parameters: the limiting factorG and quality factorQ . Exciton density at the laser threshold andG andQ The two are inversely proportional to [17]. Therefore, the optimization of the geometry of the DFB resonator is crucial to reduce the loss, which can be achieved byG andQ Quantitative. The goal of this work is to study the effect of organic film thickness on laser performance, including energy threshold and laser wavelength. First, the design of the laser is fixed. This step is done by calculating the effective refractive index of the waveguide structure in order to deduce the grating period required to obtain lasing at the ASE wavelength. The thickness of the organic film was changed from 100 nm to 300 nm, and the effective refractive index at each thickness was calculated. Second, optical simulations were performed in order to gain a physical understanding of how the laser threshold energy varies with thickness. The quality factor and confinement factor of the resonator were calculated according to the film thickness and compared with the experimental energy threshold of the organic laser device.2 . Device structure and simulation details The geometry of the grating-coupled waveguides constituting the second-order DFB organic laser studied in this work is depicted in Fig. 33. The waveguide structure consists of a gain medium (6%wt BSBCz: CBP) made of SiO with a lower refractive index₂ It consists of a grating and a high refractive index layer surrounded by air. The gain medium consisted of a 6 wt% BSBCz:CBP blend film vacuum deposited on a 2-order DFB grating. Fabrication of gratings on SiO by electron beam lithography₂ on the substrate. Fabrication of DFB lasers is described elsewhere [4]. The input parameters used for the simulation were the thickness and the refractive index of the layer. think air (n _a =1) and SiO₂ Substrate (n _s =1.46) is a semi-infinite layer. Refractive index of 6wt% BSBCz:CBP blend considered _f Equal to the refractive index of CBP reported in [18] ( _f about 1.8). The thickness of the organic film was changed from 100 nm to 300 nm. The structure of the laser is designed such that the laser oscillates at the amplified spontaneous emission (ASE) wavelength of BSB-Cz (about 477 nm) [19], [20].simulation software : Use the homemade python 3.5 software script to perform the effective refractive index calculation and Fano fitting. Use the finite element method in the RF module of the Comsol 5.2a software to extract the quality factor and limiting factor from the calculation of the eigenvalues of the resonator modes.3. Results and Discussion 3.1 Waveguide Characterization ( Effective Refractive Index Calculation ) To calculate the grating period using the Bragg condition (Equation 1), the effective index of refraction of the uniform waveguide (without grating) is requiredn _eff . In this model, the grating is ignored, so the thickness of the waveguide is the thickness of the organic film. The effective refractive index is calculated by solving the propagating wave equation [21] at a wavelength of 477 nm according to the thickness of the organic filmn _eff value. In this calculation, we consider the asymmetric waveguide to have no grating (Fig. 34(a)). In the case of an asymmetric 3-layer slab waveguide, the electric field in each region is given by:

in:

ink ₀ is the vacuum propagation constant model

,andbeta is the propagation constant of the guided mode

. The effective refractive index of the waveguide mode is calculated from the transcendental equation obtained after applying the following boundary conditions:

Figure 34(b) presents the waveguide dispersion curve derived from Equation 6 and Equation 7, which shows the effective refractive index as a function of organic film thickness at a laser wavelength of 477 nm. From these curves, one can infer the number of propagating modes at a given thickness and the cutoff thickness for a particular propagating mode. In this work, the thickness was chosen to vary from 100 nm to 300 nm. For thickness below 280 nm, only fundamental mode TE is allowed₀ oscillation. Increasing the thickness above 280 nm leads to higher order (TE₁ , TE₂ )exist. Once the effective index of refraction is calculated, one can use the Bragg condition (Eq. 1) at different film thicknesses to infer that the grating period is at l_ASE = value at 477 nm. For a film thickness of 200 nm,n _eff =1.7. The value of the grating period L satisfying the Bragg condition (Equation 1) is 280 nm. In the following, we fix the grating period at 280 nm and the grating depth at 70 nm thickness. The thickness of the organic thin film changed from only 100 nm to 300 nm.3.2 DFB Cavity optimization The resonator is described by its photon lifetime and confinement factor. The photon lifetime t represents the time a photon spends in a cavity (the rate at which photons are lost in the cavity). Photons can be lost by escaping the cavity or by absorption through the material. This photon lifetime t is related to the quality factor Q of the cavity as follows:

where w₀ is the resonant angular frequency. The Q-factor of the optical cavity is calculated in two different ways.(1) Eigenmode Computation In a first approach, the figure of merit was extracted from the calculation of the eigenvalues of the resonator modes using the finite element method in the RF module of the Comsol software. The computational domain is limited to one period unit cell of the grating. Floquet periodic boundary conditions are applied to the lateral boundaries, and scattering boundary conditions are used for the top and bottom domains [22], [23]. The natural frequency solver is used to find the propagating eigenmodes of the cavity. According to the real part and imaginary part of the eigenvalue, the Q factor is derived:

inalpha damped decay

. Additionally, the confinement factor for the eigenmodes is calculated using the following expression:

inE _norm is the normalized electric field intensity distribution of the eigenmode.(2) Fano Fitting of Reflectance Spectrum A second method for extracting the figure of merit consists of calculating the reflectance spectrum using a scattering matrix implemented in the Comsol software for normally incident TE polarized plane waves whose electric field is parallel to the grating [ref]. Subsequently, the Q-factor was obtained by fitting the resonance linewidth present in the simulated reflectance spectrum to the following Fano resonance equation (Equation 8) [24]:

inw ₀ is the center frequency,t For the life of resonance,r andt to have the same thickness and effective index of refraction as the gratingn _eff,g Amplitude reflection and transmission coefficients of a uniform thick block. In the case of binary gratings, the effective index of refraction can be described using the following effective medium theory [25]:

inff defined as raster widthw Compared with the period L. 35 shows the calculated reflectance spectra and the corresponding fitted Farno resonance curves using Equation 11 as a function of wavelength and film thickness. Reflection peaks at wavelengths of 448, 462, 472, 478 and 483 nm were observed for cavities with film thicknesses of 100, 150, 200, 250 and 300 nm, respectively. At these wavelengths, resonance occurs due to phase matching between the waves diffracted by the grating and the leaky waveguide modes [26], [27]. Thus, multiple reflections occur in the waveguide and the wavelength of the incident light is selected by the resonance of the waveguide grating. As confirmed by the calculations presented in Section 3.1 and by previously reported work [28], _f The addition makes the modaln _eff increase (Fig. 34(b)), which causes tuning of the laser wavelength. As we can see in Figure 36(a), _f The increase causes the spectral red shift of the laser emission. Experimental laser wavelengths were correlated with the Fano model and indicated in Section 3.1 "Model _f +h _g A comparison of the calculated laser wavelengths for the model is presented in Figure 36(b), whereh _g Refers to the depth of the grating. Both models provide approximately the same results, close to the experimental values, but at smaller _f (<200 nm) the gap between the experimental wavelength and the calculated wavelength is still significant (Δλ>10 nm). According to reports, when the ratioh _g / _f When exceeding 0.3 [28], at _f Exponential coupling is the dominant mechanism around 200 nm and below. When exponential coupling is more dominant than gain coupling, the laser will notλ _Bragg appeared nearby. Therefore, the deviation between the experimental and calculated laser wavelengths can be calculated by _f explained by the dominance of the exponential coupling. Figure 37(a) shows the calculatedQ factor andΓ value. for calculationQ Both methods of factoring give the same result. visible,Γ along with _f increase, exhibiting good optical confinement. This is attributed to the fundamental harmonic mode TE₀ Ofn _eff increase. However, the resonance cavityQ factor between 200 nm _f value becomes the highest. different _f measured energy thresholdE _th Presented in Figure 37(a). we can observeQ factor withE _th Inversely proportional. In addition, when _f When increasing from 100 nm to 200 nm,E _th decrease. This is attributed toQ factor andΓ increase of both. at 200 nm _f under the value,E _th shows the minimum value, and then follows _f Increase. larger _f higherE _th is attributed to the lowerQ factor. Finally, the full width at half maximum (FWHM) of the peak reflection extracted from the calculation and Fano fit was compared with the FWHM of the experimental laser emission [Fig. 37(b)]. Both the experimental and calculated FWHM values are shown to be consistent with _f The same trend is obtained for the minima.3.3 Encapsulated DFB Laser optimization In this section, CYTOP is used to calculate theG andQ factor. The input parameters for the optical simulations are the thickness of the organic thin film and the refractive index of the layer. Think CYTOP (no _CYTOP =1.35) and SiO₂ Substrate (no _SiO2 =1.46) is a semi-infinite layer. Think 6wt% BSBCz: Refractive index n of CBP film_f Equal to the reported refractive index of CBP ( _f =1.85) (1 ). BSBCz: Thickness of CBP filmd ₀ From 100 nm to 300 nm. Due to the structured top surface, in thickness (h _g -h _{g ( top )} )/2=30 nm thin layer with depthh _{g ( top )} =5 nm thin grating.3.3.1 Film Thickness Variation First, we are calculatingG andQ factor to make raster depthh _g keep constant(h _g =65 nm) while studying film thicknessd ₀ effect of the change. Table S1 shows the calculation results.surface S1 . Film thickness, resonance wavelength, quality factor and confinement factor.

When the thickness increases,G andQ factor increases, but due to the resonant wavelengthlambda ₀ ASE wavelength shift from gain material, between 200 nmd ₀ Maintain optimum thickness for device operation.3.3.2 Grating Depth Variation Second, we are calculatingG andQ factor makesd ₀ keep constant(d =200 nm) while studyingh _g The effect of change. Table S2 below shows the calculation results.surface S2 . Grating depth, resonance wavelength, quality factor and confinement factor.

By reducing the raster depth,Q factor increasesG Still pretty much the same. However, the fabrication of shallow gratings is challenging because small changes in depth can greatly affect the optical response of the grating. Although this aspect could certainly be improved in future work, the choice of a depth of 65 nm seemed most appropriate in this study.3.3.3 Comparison Between Encapsulated and Unencapsulated Devices Calculations were done using the same geometry. In the encapsulated case, the top layer was CYTOP with a refractive index of 1.35. In the unencapsulated case, CYTOP is replaced by air (no =1). In this situation,Q factor andG increases and the resonance wavelength is slightly blue-shifted, as demonstrated in Table S3.surface S3 . Comparison of resonance wavelength, quality factor and confinement factor between encapsulated and non-encapsulated devices.

However, based on the experimental results, the encapsulated devices showed better performance (FWHM) than the non-encapsulated devices. This could be due to changes in the top surface when we encapsulated the device or due to protection from moisture.3.3.4 2 The effect of the size of the step grating area The lasing threshold of BSBCz:CBP (6:94wt.%) blend mixed-stage DFB laser was experimentally determined using different sizes of the 2-stage region. The results are shown in Figure 17. It can be seen that the DFB architecture used for this study (which corresponds to a number of periods equal to 36) was not fully optimized, suggesting that further improvements in device performance should be possible by playing only on resonator structures.references 1. C. Ge, M. Lu, X. Jian, Y. Tan, and B. T. Cunningham, “Large-area organic distributed feedback laser fabricated by nanoreplica molding and horizontal dipping,” vol. 18, no. 12, pp. 12980 -12991, 2010. 2. H. Nakanotani, S. Akiyama, D. Ohnishi, M. Moriwake, M. Yahiro, T. Yoshihara, S. Tobita, and C. Adachi, “Extremely low-threshold amplified spontaneous emission of 9 ,9-disstituted-spirobifluorene derivatives and electroluminescence from field-effect transistor structure,"Adv. Funct. Mater. , vol. 17, no. 14, pp. 2328-2335, 2007. 3. G. Tsiminis, Y. Wang, P. E. Shaw, A. L. Kanibolotsky, I. F. Perepichka, M. D. Dawson, P. J. Skabara, G. A. Turnbull, and I. D. W. Samuel, " Low-threshold organic laser based on an oligofluorene truxene with low optical losses,” pp. 3-5, 2009. 4. A. S. D. Sandanayaka, K. Yoshida, M. Inoue, C. Qin, K. Goushi, J.-C. Ribierre, T. Matsushima, and C. Adachi, “Quasi-Continuous-Wave Organic Thin-Film Distributed Feedback Laser,”Adv. Opt. Mater. , vol. 4, no. 6, pp. 834-839, Jun. 2016. 5. E. R. Martins, Y. Wang, A. L. Kanibolotsky, P. J. Skabara, G. A. Turnbull, and I. D. W. Samuel, “Low-Threshold Nanoimprinted Lasers Using Substructured Gratings for Control of Distributed Feedback,"Adv. Opt. Mater. , vol. 1, no. 8, pp. 563-566, 2013. 6. V. Qaradaghi, V. Ahmadi, and G. Abaeani, “Design of organic vertical-cavity surface-emitting laser for electrical pumping,”IEEE Electron Device Lett. , vol. 33, no. 11, pp. 1616-1618, 2012. 7. M. D. McGehee, M. A. Díaz-García, F. Hide, R. Gupta, E. K. Miller, D. Moses, and A. J. Heeger, “Semiconducting polymer distributed feedback lasers,"Appl. Phys. Lett. , vol. 72, no. 13, pp. 1536-1538, 1998. 8. G. Heliotis, R. Xia, D. D. C. Bradley, G. A. Turnbull, I. D. W. Samuel, P. Andrew, and W. L. Barnes, “Blue, surface-emitting , distributed feedback polyfluorene lasers,”Appl. Phys. Lett. , vol. 83, no. 11, pp. 2118-2120, 2003. 9. A. E. Vasdekis, G. Tsiminis, J.-C. Ribierre, L. O' Faolain, T. F. Krauss, G. A. Turnbull, and I. D. W. Samuel, " Diode pumped distributed Bragg reflector lasers based on a dye-to-polymer energy transfer blend."Opt. Express , vol. 14, no. 20, pp. 9211-9216, 2006. 10. R. Osterbacka, M. Wohlgenannt, M. Shkunov, D. Chinn, and Z. V. Vardeny, “Excitons, polarons, and laser action in poly( p-phenylene vinylene) films, "J. Chem. Phys. , vol. 118, no. 19, pp. 8905-8916, 2003. 11. C. X. Sheng, R. C. Polson, Z. V. Vardeny, and D. A. Chinn, “Studies of pi-conjugated polymer coupled microlasers,”Synth. Met. , vol. 135-136, no. April, pp. 147-149, 2003. 12. M. Berggren, A. Dodabalapur, Z. N. Bao, and R. E. Slusher, “Solid-state droplet laser made from an organic blend with a conjugated polymer emitter,"Adv. Mater. , vol. 9, no. 12, pp. 968-971, 1997. 13. G. Tsiminis, Y. Wang, A. L. Kanibolotsky, A. R. Inigo, P. J. Skabara, I. D. W. Samuel, and G. A. Turnbull, “Nanoimprinted organic semiconductor laser pumped by a light-emitting diode,"Adv. Mater. , vol. 25, no. 20, pp. 2826-2830, 2013. 14. I. D. W. Samuel and G. a Turnbull, “Organic semiconductor lasers.”Chem. Rev. , vol. 107, no. 4, pp. 1272-1295, 2007. 15. H. Kogelnik and C. V. Shank, “Coupled-wave theory of distributed feedback lasers,”J. Appl. 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Adachi, “Low amplified spontaneous emission threshold and suppression of electroluminescence efficiency roll-off in layers doped with ter(9,9'-spirobifluorene),”Appl. Phys. Lett. , vol. 108, no. 13, 2016. 21. A. K. Sheridan, G. A. Turnbull, A. N. Safonov, and I. D. W. Samuel, “Tuneability of amplified spontaneous emission through control of the waveguide-mode structure in conjugated polymer films 62, vol. no. 18, pp. 929-932, 2000. 22. J.-H. Hu, Y.-Q. Huang, X.-M. Ren, X.-F. Duan, Y.-H. Li, Q . Wang, X. Zhang, and J. Wang, “Modeling of Fano Resonance in High-Contrast Resonant Grating Structures,”Chinese Phys. Lett. , vol. 31, no. 6, p. 64205, Jun. 2014. 23. T. Zhai, X. Zhang, and Z. Pang, “Polymer laser based on active waveguide grating structures.”Opt. Express , vol. 19, no. 7, pp. 6487-6492, 2011. 24. A. E. Miroshnichenko and Y. S. Kivshar, “Fano resonances in nanoscale structures,” vol. 82, no. September, pp. 2257-2298, 2010. 25 . M. Foldyna, R. Ossikovski, A. De Martino, B. Drevillon, E. Polytechnique, and P. Cedex, “Effective medium approximation of anisotropic lamellar nanogratings based on Fourier factorization,” vol. 14, no. 8, pp. . 3055-3067, 2006. 26. S. S. Wang and R. Magnusson, “Theory and applications of guided-mode resonance filters.,”Appl. Opt. , vol. 32, no. 14, pp. 2606-2613, 1993. 27. T. Khaleque and R. Magnusson, “Light management through guided-mode resonances in thin-film silicon solar cells,”J. Nanophotonics , vol. 8, no. 1, p. 83995, 2014. 28. V. Navarro-Fuster, I. Vragovic, E. M. Calzado, P. G. Boj, J. A. Quintana, J. M. Villalvilla, A. Retolaza, A. Juarros, D. Otaduy , S. Merino and M. A. Díaz-García, “Film thickness and grating depth variation in organic second-order distributed feedback lasers,” J. Appl. Phys. Vol.112, no.4, pp. 43104, 2012.chapter B . mixed order DFB Laser properties of the device Using BSBCz pure films or BSBCz:CBP (6:94 wt.%) blended films under pulsed optical pumping of a nitrogen laser delivering 800 ps pulses at a wavelength of 337 nm at a repetition rate of 20 Hz Laser properties of encapsulated mixed-order DFB devices as gain medium. In the case of CBP blended films, the excitation light is mainly absorbed by the CBP host. However, the large spectral overlap between CBP emission and BSBCz absorption ensures efficient Förster-type energy transfer from host molecule to guest molecule (2 -6 ). This was confirmed by the absence of CBP emission under 337 nm light excitation. Figures 19A-19E show the emission spectra collected perpendicular to the surface of BSBCz films and BSBCz:CBP (6:94 wt.%) films at different excitation intensities below and above the threshold. At low excitation intensity, the corresponding DFB grating (2 ) of the Bragg dip in the photoresist band. The small change in the position of the Bragg dip is presumably due to the slightly different refractive indices of the blended and pure films (2 -6 ). As the pump intensity was increased above a critical threshold, a narrow emission peak appeared in both pure and blended devices, indicating the onset of lasing. It can also be seen that the intensity of the lasing peak increases faster than the photoluminescent background, providing evidence of a non-linearity associated with stimulated emission. The laser wavelength was found to be 484 nm for the blended film and 481 nm for the pure film. 19C-19D show output emission intensity and full width at half maximum (FWHM) as a function of pump intensity for two DFB devices. It is found that the FWHM becomes lower than 0.2 nm at high excitation intensity. The laser threshold value of the DFB laser is determined by the sudden change in the output intensity. Devices based on pure and blended films were found to exhibit 0.22 μJ cm^{− 2} and 0.09 μJ cm^{− 2} The laser threshold value. In both cases, these values are below the previously reported threshold values for amplified spontaneous emission (ASE) and second-order DFB lasing in BSBCz:CBP blends (2 -6 ), supporting the possibility of hybrid-order gratings for high-efficiency organic solid-state lasers.chapter C . optical gain From these experimental ASE data, net gain and loss coefficients can be determined and their values are listed in Table S4.surface S4 . Pulse width, excitation power, net gain and loss coefficient.

These ASE results provide clear evidence that larger net optical gains can be achieved in BSBCz-based films in the CW state. Therefore, this clearly supports our statement that BSBCz is one of the best candidates for CW lasers and quasi-CW lasers.chapter D. . transient absorption The results in Figure 27A indicate that the PL intensity remains constant after several μs of illumination. This implies that there is no quenching of singlet excitons by STA in the device. Figure 27C also shows that there is no significant spectral overlap between the laser and triplet absorption spectra. Their results provide clear evidence that there is no detrimental triplet loss in the gain medium used in this study. From these data, we also estimated the stimulated emission cross section as previously reportedσ _em and triplet excited state cross sectionσ _TT (3 , 9 ). under 480 nmσ _em 2.2×10^{− 16} cm² , which is obviously greater than 3.0×10^{− 19} cm² Ofσ _TT , indicating that the triplet absorption has little effect on the long-pulse regime. We estimate the triplet lifetime in solution separately (τ _TT ), the triplet absorption cross section (σ _TT ) and intersystem crossing yield (f _ISC ),τ _TT =5.7×10³ the s^-1 ,σ _TT =3.89×10^-17 cm² (at 630 nm, Figure 27D) andf _ISC =0.04. Estimated by excitation power dependence of transient absorption compared to benzophenone as reference (Fig. 27E)f _ISC (9 ). However, it should be emphasized that using our transient absorption measurement system, we could not observe any triplet specific gravity in the film. For example, due tof _PL For values close to 100%, intersystem crossing in blended films is negligible. Overall, the measured higher thanE. _{the th} The emission spectrum does not largely overlap with the triplet absorption spectrum, resulting in a large net gain in light amplification in the long pulse regime. Therefore, we believe that BSBCz is one of the best candidates for CW lasers and quasi-CW lasers.chapter E. . thermal simulation To probe the temperature distribution within the device, a transient 2D heat transfer simulation was performed using COMSOL 5.2a. Figure 38 shows a schematic diagram of the geometry of a laser device. It should be noted that we have ignored the grating in this simulation. The local difference equation governing the temperature distribution is expressed as:

inρ is the material density,C _p is the specific heat capacity,T is the temperature,t for time,k is thermal conductivity andQ is the laser heat source term. The laser pump beam has a Gaussian shape. Due to the circular symmetry of the laser beam, the heat transfer equation is solved in cylindrical coordinates. For a pulsed Gaussian laser beam, the heat source is written as follows (10 ):

ina is the absorption coefficient,R is the reflection of the pump beam at the bottom facet of the device,P is the incident pump power reaching the gain region,r andz is the spatial coordinate,r ₀ 1/ of the pump laser beame ² radius,r =0 is the center of the laser beam,z _g is the z-coordinate of the interface between the gain region and the top layer (see Figure 38),h (t ) for a pulse width witht _p The rectangular pulse function,h _g Absorbed in the gain region in the absence of the laser field (11 ) The fraction of the pump power converted to heat in the case of ), which is given by:

inf _PL is the fluorescence quantum yield (f _PL (BSBCz:CBP)=86%),lambda _{Pump Pu} is the pump laser wavelength, andlambda _laser is the extracted laser wavelength. Regarding the boundary conditions in the radial direction, a symmetric boundary condition is used at the axis of rotation. Apply thermal insulation boundary conditions (ignoring air convection) at the bottom, top, and edge surfaces. The radius of the device was set to 2.5 mm. Power density of 2 kW/cm² . Table S5 presents the thermophysical and geometric parameters used for the simulations obtained from the COMSOL database. For the BSBCz:CBP layer, we choose the same thermal parameters as in Ref (11) for the organic material.surface S5 . Thermophysical parameters and geometric parameters of materials.

After absorbing the pump laser energy, the BSBCz layer acts as a heat source. The heat generated is transferred by conduction towards the top and bottom layers.1.1 Pulse Width Variation Figure 39 and Figure 40 show the pulse widths of 10, 30 and 40 ms each timet _p Maximum temperature rise after pumping and temperature rise at the interface of the BSBCz/CYTOP layer. These simulation results demonstrate that the temperature rise caused by long-pulse pump irradiation increases with pulse duration, but this effect tends to saturate for pulses longer than 30 ms. It can also be seen from these calculations that the temperature rise is not expected to increase significantly with the number of incident pulses.1.2 exist 10 ms Effect of encapsulation in case of pulse width The simulation results in Figure 41 provide clear evidence of the importance of encapsulation for use in our device to improve thermal management in devices operating under long pulse light irradiation.1.3 CYTOP thickness change As shown in Figure 42, due to the low thermal conductivity of CYTOP, increasing the CYTOP thickness results in an increase in temperature in the gain region. Although it was found that encapsulation of DFB lasers by CYTOP was critical for improving device performance under long-pulse light excitation, the poor thermal conductivity of CYTOP is clearly a limiting factor, and this aspect should be addressed in future studies by selecting more appropriate capsules. encapsulation materials in order to demonstrate the actual CW organic semiconductor technology.references 1. D. Yokoyama, A. Sakaguchi, M. Suzuki, C. Adachi, Horizontal orientation of linear-shaped organic molecules having bulky substitutes in neat and doped vacuum-deposited amorphous films.Org. Electron .10 (1), 127-137 (2009). 2. A. S. D. Sandanayaka, K. Yoshida, M. Inoue, K. Goushi, J. C. Ribierre, T. Matsushima, C. Adachi, Quasi-continuous-wave organic thin film distributed feedback laser .Adv. Opt. Mater. 4 , 834-839 (2016). 3. H. Nakanotani, C. Adachi, S. Watanabe, R. Katoh, Spectrally narrow emission from organic films under continuous-wave excitation.Appl. Phys. Lett. 90 , 231109 (2007). 4. D. Yokoyama, M. Moriwake, C. Adachi, Spectrally narrow emissions at cutoff wavelength from edges of optically and electrically pumped anisotropic organic films.J. Appl. Phys. 103 , 123104 (2008). 5. H. Yamamoto, T. Oyamada, H. Sasabe, C. Adachi, Amplified spontaneous emission under optical pumping from an organic semiconductor laser structure equipped with transparent carrier injection electrodes.Appl. Phys. Lett. 84 , 1401 (2004). 6. T. Aimono, Y. Kawamura, K. Goushi, H. Yamamoto, H. Sasabe, C. Adachi, 100% fluorescence efficiency of 4,4'-bis[(N -carbazole)styryl]biphenyl in a solid film and the very low amplified spontaneous emission threshold.Appl. Phys. Lett. 86 , 071110 (2005). 7. M. D. Mcgehee, A. J. Heeger, Semiconductor (conjugated) polymers as materials for solid-state lasers.Adv. Mater. 12 , 1655-1668 (2000). 8. J. C. Ribierre, G. Tsiminis, S. Richardson, G. A. Turnbull, I. D. W. Samuel, H. S. Barcena, P. L. Burn, Amplified spontaneous emission and lasing properties of bisfluorene-cored dendrimers.Appl. Phys. Lett. 91 , 081108 (2007). 9. S. Hirata, K Totani, T. Yamashita, C. Adachi, M. Vacha, Large reverse saturated absorption under weak continuous incoherent light.Nature Materials. 13 , 938-946 (2014). 10. Z. Zhao, O. Mhibik, T. Leang, S. Forget, S. Chénais, Thermal effects in thin-film organic solid-state lasers.Opt. Express. twenty two , 30092-30107 (2014). 11. S. Chenais, F. Druon, S. Forget, F. Balembois, P. Georges, On thermal effects in solid-state lasers: The case of ytterbium doped materials,Prog. Quantum Electron. 30 (4), 89-153 (2006).[ 5 ] Electrically Driven Organic Semiconductor Laser Diodes overview Despite significant advances in the efficiency of optically pumped organic semiconductor lasers and their applications, electrically driven organic laser diodes have not yet been realized. Here we report the first demonstration of an organic semiconductor laser diode. The reported device incorporates a mixed-order dispersed feedback SiO₂ The grating is incorporated into the organic light emitting diode structure. Up to 3.30 kA cm^{− 2} The current density was injected into the device, and the blue laser was observed to be higher than about 0.54 kA cm^{− 2} the threshold value. The realization of organic semiconductor laser diodes is mainly due to the selection of high-gain organic semiconductors that do not exhibit triplet absorption losses at laser wavelengths and the containment of electroluminescent efficiency roll-off at high current densities. This represents a major advance in the field of organic electronic devices and a first step towards novel cost-effective organic laser diode technology that enables full integration of organic optoelectronic circuits.A detailed description The properties of optically pumped organic semiconductor lasers (OSLs) have been greatly improved over the past two decades due to major advances in both the development of high-gain organic semiconductor materials and the design of high-quality factor resonator structures^1-5 . Advantages of organic semiconductors as gain media for lasers include their high photoluminescence quantum yield (PLQY) and large stimulated emission cross section, their chemical tunability, their broad emission spectrum across the visible region, and their ease of manufacture . Due to recent advances in low-threshold decentralized feedback (DFB) OSLs, it is demonstrated that optical pumping of nanosecond-pulsed phosphors by electrically driving them provides a path toward new compact and low-cost visible laser technologies. way⁶ . Miniaturized organic lasers of this type are particularly promising in lab-on-a-chip applications, chemical sensing, and biological analysis. However, to achieve the full integration of organic photonic circuits and optoelectronic circuits, electrically actuating organic semiconductor laser diodes (OSLDs) is required, which has so far remained an unrealized scientific challenge. The problems preventing direct electrical pumping of organic semiconductor devices by lasers are mainly due to optical losses from electrical contacts and additional triplet and polaron losses that occur at high current densities^4,5,7-9 . Different approaches have been proposed to solve these problems involving, for example, the use of triplet quenchers^{10 - 12} To suppress triplet absorption loss and singlet quenching by mutual destruction of singlet-triplet excitons, and reduce the active area of the device¹³ To spatially separate the exciton formation and exciton radiative decay regions and minimize the polariton quenching process. Considering the current advanced technology of optically pumped organic semiconductor DFB laser⁵ A careful combination of these approaches with optimization of the device structure can lead to electrically driven lasing emission from organic thin films. Previous studies suggested that higher than a few kA/cm would be required if the additional losses associated with electrical pumping were to be fully contained² The current density to achieve laser from OSLD¹⁴ . In exhibiting an amplified spontaneous emission (ASE) threshold below 0.5 μJ/cm² Among different organic semiconductor thin films,⁵ One of the most promising molecules for observing lasing emission under electrical pumping is 4,4'-bis[(N-carbazole)styryl]biphenyl (BSBCz) (see the chemical structure)¹⁵ . The ASE threshold of BSBCz-based films was reported to be as low as 0.30 μJ cm under 800 ps pulsed light excitation^{−2 16} . Meanwhile, another work demonstrated up to 2.8 kA cm under pulse operation with a pulse width of 5 μs^{− 2} High current densities can be injected into BSBCz-based organic light-emitting diodes (OLEDs)¹³ . These devices exhibit maximum electroluminescent external quantum efficiency (EQE) values above 2%. Furthermore, the efficiency roll-off due to singlet-thermal and singlet-polaron mutual destruction at high current densities is substantially reduced by shrinking one dimension of the current injection/transportation region to 50 nm. Recently, quasi-CW lasing at 80 MHz and true CW lasing lasting at least 30 ms were demonstrated in an optically pumped BSBCz-based organic DFB laser¹⁷ . Such unprecedented performance was achieved because the PLQY of BSBCz was close to 100% in 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) blends and because There is no significant triplet absorption loss at the laser wavelength of BSBCz films. Here, by combining an inverted OLED structure with a mixed-order DFB SiO2 integrated in the active region of the device₂ The gratings were combined to demonstrate electrically driven lasing emission from BSBCz thin films, thus providing the first definitive evidence of electrically driven lasing emission from an organic semiconductor. The fabrication method and architecture of the OSLD developed in this study are schematically shown in Figures 43 to 45 (see the detailed description of the experimental procedures in the Materials and Methods section). First, 100 nm thick dielectric SiO₂ layer was sputtered onto a pre-cleaned patterned indium tin oxide (ITO) glass substrate. We then design a hybrid-order DFB grating with a first-order Bragg scattering region surrounded by a second-order Bragg scattering region that produces strong optical feedback and provides efficient vertical extraction of the laser emission, respectively.^17,18 . In DFB lasers, it is known that when the Prague condition is satisfied^4,19 (mλ_Bragg = 2n_eff Λ) laser oscillation occurs, where m is the diffraction order,l _Bragg is the Bragg wavelength, n_eff is the effective refractive index of the gain medium, and Λ is the grating period. Using the n reported for BSBCz_eff value andl _Bragg value^20,21 , the grating periods of the mixed-order (m=1, 2) DFB laser devices are calculated to be 140 nm and 280 nm, respectively. These mixed-order DFB gratings were engraved on SiO using electron beam lithography and reactive ion etching.₂ Within the 140×200 μm area in the layer (FIG. 46A). As demonstrated by the scanning electron microscopy (SEM) images in Figure 46B, the DFB gratings fabricated in this work have periods of 140±5 nm and 280±5 nm and a grating depth of about 65±5 nm, which is perfectly It fully complies with our specifications provided above. The lengths of each 1st-order and 2nd-order DFB gratings are about 10 µm and 15.1 µm, respectively. Energy dispersive X-ray spectroscopy (EDX) analysis was then performed to ensure that the ITO layer was not damaged during grating fabrication and to ensure complete removal of SiO in the etched areas₂ layer. The EDX results shown in Figures 46C and 46D provide evidence that charge injection from ITO to the organic semiconductor layer deposited on top of the DFB grating can occur in the etched regions where the ITO contacts are located. In addition, we propose that DFB resonators can also be fabricated using a low-cost simple nanoimprint lithography process (Fig. 45). As shown by the schematic representation shown in Figure 47A, the OSLD fabricated in this work has the following simple inverted OLED structure vapor-deposited on top of the DFB grating: ITO (100 nm)/20 wt.%Cs: BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm). In such inverted device structures, electron injection into the organic layer is improved by Cs-doped BSBCz films in the region close to the ITO contacts, while MoO₃ Used as a hole injection layer (Figure 48 to Figure 49). As shown in Figure 50, the surface morphology of all layers presents a grating structure with a surface modulation depth of 20 nm to 30 nm. Although the most efficient OLEDs generally use a multilayer architecture to optimize charge balance^22,23 , but charge accumulation can occur at organic heterointerfaces at high current densities, which can be detrimental to device performance and stability^{twenty four} . The OSLDs fabricated in this work contain only BSBCz as the organic semiconductor and are specifically designed to minimize the number of organic heterointerfaces. It should be noted that also fabricated without SiO₂ DFB gratings and used as a reference to obtain additional information on the effect of gratings on electroluminescent properties. In addition, we desire the SiO₂ Organic semiconductor laser diodes with different one-dimensional DFB resonator structures were fabricated in , ITO, and polymers or on top of active layers (FIGS. 51A-51D). As shown in Figure 52, organic semiconductor laser diodes with a two-dimensional DFB resonator structure are also promising for lower threshold 2D DFB lasers. Figure 47B and Figures 53A-53D show optical microscope images of an OSLD, and Figure 47C shows those optical microscope images of a reference OLED without a grating, both operated at 4.0 V of direct current (DC). Electroluminescence is emitted uniformly from the active area of the reference OLED. In the case of an OSLD, a more intense emission can be seen from the 2-stage DFB grating region of the OSLD, which is specifically designed to facilitate vertical light extraction. Current-voltage (J-V) and EQE-J curves measured in representative devices with and without DFB gratings are shown in Figures 47D-47E. Devices were characterized under both DC and pulsed (with voltage pulse width of 500 ns and repetition rate of 100 Hz) conditions. Estimating the active area of the OSLD from SEM and laser microscope images, it is necessary to calculate the current density injected into the device. Reference devices under DC and pulsed operation respectively exhibit 70 A cm before device breakdown^{− 2} and 850 A cm^{− 2} The maximum current density (J_max ). Due to the small active device area^13,25 The reduction of the Joule heat, the OSLD obviously exhibited 80 A cm under DC and pulse operation respectively^{− 2} and 3220 A cm^{− 2} higher J_max . All BSBCz devices were found to exhibit maximum EQE values above 2% at lower current densities. However, at DC operation above 15 A cm^{− 2} A significant efficiency roll-off in the OSLD and the reference device was observed at current densities of 1000 Å, which can be attributed to thermal degradation of the organic gain medium. Under pulsed operation, the reference device exhibited a higher than 410 A cm^{− 2} Efficiency roll-off at a current density of , which is in line with previously reported¹³ in the result. More importantly, the efficiency roll-off in OSLDs was suppressed under pulsed operation and even found to substantially increase the EQE above 800 A cm^{− 2} To achieve the maximum value of 3.3%. When the current density increases above 3200 A cm^{− 2} , the rapid decrease in EQE was speculated to be due to the thermal degradation of the organic semiconductor. As shown in Figure 54, the electroluminescence spectrum of the reference device is similar to the steady-state PL spectrum of the BSBCz pure film and does not change with changes in current density. Figure 53E, Figure 55A, Figure 55C and Figure 56A show the evolution of the electroluminescence spectra of several OSLDs at different current densities of pulsed operation. These spectra were measured from the ITO side of the OSLD in a direction perpendicular to the plane of the substrate. It can be clearly seen that when J becomes higher than 800 A cm^{− 2} A strong spectral line-narrowing effect is produced at 456.8 nm. For further insight, output intensity and full width at half maximum (FWHM) as a function of current density are plotted in Figure 53F, Figure 55B, Figure 55D and Figure 56B. While the FWHM of the steady-state PL spectrum of the BSBCz pure film is about 35 nm, its value decreases to below 0.2 nm at the highest current density. At the same time, a sudden change in the slope efficiency of the output intensity was also observed, which is consistent with the state of the EQE-J curve and can be used to determine the 960 A cm^{− 2} the threshold value. Similar to that seen in the EQE-J curve, when J > 3.2 kA cm^{− 2} When , the output intensity decreases with J, which is attributed to thermal degradation leading to device breakdown. In this state, however, it is notable that the emission spectrum of the OSLD remains extremely steep. The observed regime clearly indicates that optical amplification occurs at high current densities and the OSLD exhibits lasing emission above the lasing threshold. The quest for the first organic semiconductor laser diode has been associated with several controversial reports in the past, implying that attention should be paid to providing electrically driven laser emission before claiming that the OSLD fabricated in this study⁹ . First, several studies^{20 , 26 , 27} It is shown that edge emission from waveguide modes of organic light-emitting devices can lead to extremely strong line-narrowing effects without laser amplification. In contrast to these previous works, the emission from our OSLD was detected in the direction perpendicular to the substrate plane and exhibited a clear threshold state. It should also be emphasized that the ASE linewidth of organic thin films is usually in the range of several nm, while the FWHM of organic DFB lasers can be much lower than 1 nm⁵ . In the case of FWHM below 0.2 nm, the emission spectrum from our OSLD cannot be attributed solely to ASE and corresponds to elements usually obtained in optically pumped organic DFB lasers. Second, previous reports demonstrated extremely narrow emission spectra by inadvertently exciting transitions in ITO.²⁸ The atomic spectral lines of ITO include those at 410.3 nm, 451.3 nm and 468.5 nm.²⁹ The emission peak wavelength of the OSLD in Figure 55A is 456.8 nm, which cannot be attributed to emission from ITO. It should also be emphasized that the emission of the OSLD should be characteristic of the resonator mode, and thus the output should be very sensitive to any modification of the laser cavity. A simple way to tune the emission wavelength in an optically pumped organic DFB laser is to vary the grating period^{4 , 5 , 30 , 31} . Figures 55C-55D show the emission spectra at different current densities and the OSLD output intensity as a function of current density for grating periods of 300 nm (for 2nd order scattering) and 150 nm (for 1st order scattering), respectively. The device demonstrates a FWHM as low as 0.16 nm and a threshold of 1.07 kA cm at 475.5 nm^{− 2} The laser peak (Figure 57). In addition, we demonstrate organic DFB lasing based on BSBCz films with a modified resonator design (Fig. 58). Since laser radiation extracted by second-order gratings represents a loss channel, these lasers generally exhibit higher thresholds compared to their first-order counterparts. To study the trade-off between extraction and thresholding, we fabricated gratings with different widths and with first-order and second-order regions. The thresholds were deduced from the laser input-output curves and plotted against the width of the second-order region in FIG. 59 . It can be seen that the oscillation threshold increases linearly with the size of the second-order region. This can be understood as it is proportional to the waveguide loss in terms of laser threshold, which increases linearly with increasing period. Thus, the threshold of a mixed-order resonator increases as the fraction of light extracted, but remains low even for strong extraction. By varying the grating parameters, the OSLD can thus be tuned to have optimized properties (low threshold and high extraction). Figure 56B shows the emission spectra at different current densities and for grating periods with 300 nm (for 2nd order scattering) and 150 nm (for 1st order scattering) respectively and 4 first order periods and 12 second order periods The OSLD output intensity varies with current density (FIG. 60). The device demonstrates a FWHM as low as 0.18 nm at 500.5 nm and a threshold of 540 A cm^{− 2} Laser Peak. This clearly provides evidence that the laser emission from our OSLD is largely influenced by the DFB resonator structure, and this can be used to tune the laser wavelength over a range of wavelengths. Laser emission from an OSLD should also follow some rules about output beam polarization, output beam shape and temporal coherence⁹ guidelines. As shown in Figure 61, the output beam of the OSLD is largely linearly polarized along the grating pattern, providing clear evidence of true one-dimensional DFB laser action in electrically driven devices. Another important issue that needs to be clarified is to see how the lasing threshold of electrically driven OSLDs compares to that obtained by optical pumping. Figure 62 shows the lasing characteristics of an OSLD optically pumped through the ITO side by a laser diode delivering a 500 ns pulse at an excitation wavelength of 405 nm. Lasing emission occurs at 481 nm, which coincides with an electrically driven laser wavelength. The laser threshold measured under optical pumping is about 450 W cm^{− 2} , which is higher than the 36 W cm obtained in an optically pumped BSBCz-based DFB laser without two electrodes^{− 2} value. It should be noted that the thicknesses of the different layers used for the OSLD have been optimized in this work to minimize optical losses due to the presence of these electrodes. Assuming no additional loss mechanisms in BSBCz OSLD operation at high current densities, threshold values measured in an optically pumped setup indicate that electrically driven lasing should achieve current densities higher than 1125 A cm^{− 2} . Similar thresholds for optical and electrical pumping have been shown to be nearly contained at high current densities³² Below are the additional losses (including exciton mutual destruction, triplet and polaron absorption, quenching by high electric fields, Joule heating) that generally occur in organic electroluminescent devices. This is in full agreement with the fact that no electroluminescent efficiency roll-off was observed in OSLDs under severe pulsed electrical excitation. To explain such results, it should be remembered that BSBCz thin films do not exhibit significant triplet absorption at laser/ASE wavelengths, and that they exhibit very weak quenching of the singlet state by singlet-triplet mutual destruction. Importantly, previous work has shown that further reductions in device active area can be used to separate exciton formation from exciton radiative decay and substantially reduce the polaron/thermal quenching process. We also fabricated a device with nine DFBs on one chip as shown in Figure 63, and this device provided effective output of laser emission. For low-threshold organic semiconductor laser diodes, we have also successfully fabricated circular DFB resonators (Fig. 64-65). In conclusion, this study demonstrates the first realization of an electrically driven organic semiconductor laser diode implementing a mixed-order decentralized feedback SiO₂ The resonator into the active area of the OLED structure. Specifically, the device exhibits a critical current density as low as 540 A cm^{− 2} The blue laser emits. Different criteria regarding emission linewidth, polarization, and threshold can be used to distinguish laser emission from other phenomena that have been carefully examined and fully support the claim that this is the first observation of electrically driven lasers in organic semiconductors. This report opens up new opportunities and perspectives in organic photonics and should obviously serve as a strong basis for the future development of organic semiconductor laser diode technology that applies simple, cheap and tunable laser sources and its suitability for complete and straightforward integration into organic-based optoelectronic platforms.Materials and methods Device fabrication and characterization Indium tin oxide (ITO)-coated glass substrates (100 nm ITO, Atsugi Micro Co.) were cleaned by ultrasonic treatment followed by UV ozone treatment using neutral detergent, pure water, acetone and isopropanol. 100 nm thick SiO at room temperature₂ DFBs were engraved on the ITO substrate by sputtering on 100 nm ITO-coated glass substrates. The argon pressure was 0.2 Pa during sputtering. The RF power was set to 100 W (Figure 43 and Figure 44). The substrate was cleaned again by ultrasonic treatment followed by UV ozone treatment using isopropanol. The silicon dioxide surface was treated with hexamethyldisilazane (HMDS) by spin coating at 4000 rpm for 15 s and annealed at 120 °C for 120 s. A resist layer with a thickness of about 70 nm was spin-coated on the substrate at 4000 rpm for 30 s from a ZEP520A-7 solution (ZEON Co.) and baked at 180° C. for 240 s. Use a cm with 0.1 nC^{− 2} A dose-optimized JBX-5500SC system (JEOL) was used for electron beam lithography to draw the grating pattern on the resist layer. After electron beam irradiation, the pattern was developed in a developer solution (ZED-N50, ZEON Co.) at room temperature. The patterned resist layer was used as an etch mask while using the EIS-200ERT etch system (ELIONIX) with CHF₃ Plasma etches the substrate. To completely remove the resist layer from the substrate, use the FA-1EA Etching System (SAMCO) with O₂ Plasma etches the substrate. Etching conditions were optimized to completely remove SiO from pitch modulation between DFBs₂ Until ITO touches. The grating formed on the silicon dioxide surface was observed using a SEM (SU8000, Hitachi) (FIG. 46B). EDX (at 6.0 kV, SU8000, Hitachi) analysis was performed to confirm the complete removal of SiO from the spacing between DFBs₂ (Figure 46C and Figure 46D). The DFB substrate was cleaned by conventional ultrasonic treatment. Then by at 2.0 × 10^{− 4} Thermal evaporation under the pressure of Pa in 0.1 nm s^{− 1} to 0.2 nm s^{− 1} The total evaporation rate of the organic layer and the metal electrode is placed in a vacuum with SiO₂ Insulator on DFB substrate to fabricate indium tin oxide (ITO) (100 nm)/20 wt% Cs: BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm) structure i-OLED. SiO remaining on the surface of ITO₂ layer acts as an insulator. Therefore, the current region of the OLED is limited to the DFB region where the BSBCz is in direct contact with the ITO. A reference OLED with an active area of 140 × 200 µm was also fabricated using the same current field. Current density-voltage-EQE (J-V-EQE) characteristics (DC) of OLEDs were measured at room temperature using an integrating sphere system (A10094, Hamamatsu Photonics). Measured under pulse driving using pulse generator (NF, WF1945), amplifier (NF, HSA4101) and photomultiplier tube (PMT) (C9525-02, Hamamatsu Photonics)J -V -L characteristic. Both the PMT response and the driving square wave signal were monitored on a multi-channel oscilloscope (Agilent Technologies, MSO6104A). Rectangular pulses with a pulse width of 500 ns, a pulse period of 5 μs and a repetition frequency of 100 Hz were applied in a device with varying peak current.Spectrum measurement The emitted laser light perpendicular to the device surface was collected using an optical fiber connected to a multi-channel spectrometer (PMA-50, Hamamatsu Photonics) and placed 3 cm away from the device. For CW operation, a CW laser diode (NICHIYA, NDV7375E, maximum power 1400 mW) was used to generate excitation light with an excitation wavelength of 405 nm. In these measurements, pulses were delivered using an acousto-optic modulator (AOM, Gooch & Housego) triggered by a pulse generator (WF 1974, NF Co.). The excitation light is concentrated on the 4.5×10 of the device through the lens and the slit^{− 5} cm² and the emitted light was collected using a frame eye (C7700, Hamamatsu Photonics) with a time resolution of 100 ps connected to a digital camera (C9300, Hamamatsu Photonics). Emission intensities were recorded using a photomultiplier tube (PMT) (C9525-02, Hamamatsu Photonics). Both the PMT response and the driving square wave signal were monitored on a multi-channel oscilloscope (Agilent Technologies, MSO6104A). The same illumination and detection angles were used for this measurement as previously described. All measurements were performed under nitrogen atmosphere to prevent any degradation caused by moisture and oxygen.references 1. Tessler, N., Denton, G. J. & Friend, R. H. Lasing from conjugated-polymer microcavities.Nature 382 , 695-697 (1996). 2. Kozlov, V. G., Bulović, V., Burrows, P. E. & Forrest, S. R. Laser action in organic semiconductor waveguide and double-heterostructure devices.Nature 389 , 362-364 (1997). 3. Hide, F.et al. Semiconductor polymers: a new class of solid-state laser materials.science 273 , 1833 (1996). 4. Samuel, I. D. W. & Turnbull, G. A. Organic semiconductor lasers.Chem. Rev. 107 , 1272-1295 (2007). 5. Kuehne, A. J. C. & Gather M. C. Organic lasers: recent development on materials, device geometries and fabrication techniques.Chem. Rev. in press. 6. Tsiminis, G.et al. Nanoimprinted organic semiconductor lasers pumped by a light-emitting diode.Adv. Mater. 25 , 2826-2830 (2013). 7. Baldo, M. A., Holmes, R. J. & Forrest, S. R. Prospects for electrically pumped organic lasers.Phys. Rev. B 66 , 035321 (2002). 8. Bisri, S. Z., Takenobu, T. & Iwasa, Y. The pursuit of electrically-driven organic semiconductor lasers.J. Mater. Chem. C 2 , 2827-2836 (2014). 9. Samuel, I. D. W., Namdas, E. B. & Turnbull, G. A. How to recognize lasing.Nature Photon. 3, 546-549 (2009). 10. Sandanayaka, A. S. D.et al. Improvement of the quasi-continuous-wave lasing properties in organic semiconductor lasers using oxygen as triplet quencher.Appl. Phys. Lett. 108 , 223301 (2016). 11. Zhang, Y. F. & Forrest, S. R. Existence of continuous-wave threshold for organic semiconductor lasers.Phys. Rev. B 84 , 241301 (2011). 12. Schols, S.et al. Triplet excitation scavenging in films of conjugated polymers.Chem. Phys. Chem. 10 , 1071-1076 (2009). 13. Hayashi, K.et al. Suppression of roll-off characteristics of organic light-emitting diodes by narrowing current injection/transport area to 50 nm.Appl. Phys. Lett. 106 , 093301 (2015). 14. Gärtner, C.et al. The influence of annihilation processes on the threshold current density of organic laser diodes.J. Appl. Phys. 101 , 023107 (2007). 15. Sandanayaka, A. S. D.et al. Quasi-continuous-wave organic thin film distributed feedback laser.Adv. Opt. Mater. 4 , 834-839 (2016). 16. Aimono, T.et al. 100% fluorescence efficiency of 4,4'-bis[(N-carbazole)styryl]biphenyl in a solid film and the very low amplified spontaneous emission threshold.Appl. Phys. Lett. 86 , 71110 (2005). 17. Sandanayaka, A. S. D.et al. Continuous-wave operation of organic semiconductor lasers.Submitted 18. Karnutsch, C.et al. Improved organic semiconductor lasers based on a mixed-order distributed feedback resonator design.Appl. Phys. Lett. 90 131104 (2007). 19. Chénais, S. & Forget, S. Recent advances in solid-state organic lasers.Polym. Int. 61 , 390-406 (2012). 20. Yokoyama, D.et al. Spectrally narrow emissions at cutoff wavelength from edges of optically and electrically pumped anisotropic organic films.J. Appl. Phys. 103 , 123104 (2008). 21. Yamamoto, H.et al. Amplified spontaneous emission under optical pumping from an organic semiconductor laser structure equipped with transparent carrier injection electrodes.Appl. Phys. Lett. 84 , 1401 (2004). 22. Kim, S. Y.et al. Organic light-emitting diodes with 30% external quantum efficiency based on horizontally oriented emitter.Adv. Funct. Mater. twenty three , 3896-3900 (2013). 23. Uoyama, H.et al. Highly efficient organic light-emitting diodes from delayed fluorescence.Nature 492 , 234-238 (2012). 24. Matsushima, T. & Adachi, C. Suppression of exciton annihilation at high current densities in organic light-emitting diode resulting from energy-level alignments of carrier transport layers.Appl. Phys. Lett. 92 , 063306 (2008). 25. Kuwae, H.et al. Suppression of external quantum efficiency roll-off of nanopatterned organic light-emitting diodes at high current densities.J. Appl. Phys. 118 , 155501 (2015). 26. Bisri, S. Z.et al. High mobility and luminescent efficiency in organic single-crystal light-emitting transistors.Adv. Funct. Mater. 19 , 1728-1735 (2009). 27. Tian, Y.et al. Spectrally narrowed edge emission from organic light-emitting diodes.Appl. Phys. Lett. 91 , 143504 (2007). 28. El-Nadi, L.et al. Organic thin film materials producing novel blue laser.Chem. Phys. Lett. 286 , 9-14 (1998). 29. Wang, X., Wolfe, B. & Andrews, L. Emission spectrum of group 13 metal atoms and indium hybrids in solid H₂ and D₂ .J. Phys. Chem. 108 , 5169-5174 (2004). 30. Ribierre, J. C.et al. Amplified spontaneous emission and lasing properties of bisfluorene-cored dendrimers.Appl. Phys. Lett. 91 , 081108 (2007). 31. Schneider, D.et al. Ultrawide tuning range in doped organic solid-state lasers.Appl. Phys. Lett. 85 , 1886 (2004). 32. Murawski, C., Leo, K. & Gather, M. C. Efficiency roll-off in organic light-emitting diodes.Adv. Mater. 25 , 6801-6827 (2013).Electrical Simulation of Distributed Feedback Electrically Driven Organic Laser 1. Device model and parameters In this study, so-called "first-generation models" are used to describe charge transport in organic light-emitting diodes (OLEDs). In this model, the electron density is solved by self-consistently using a two-dimensional time-independent drift-diffusion modelno , hole densityp And electrostatic potential Ψ. The Poisson equation relates the electrostatic potential Ψ to the space charge density as follows:

Where F is the vector electric field, q is the elementary charge, ε_r is the relative permittivity of the material and ε₀ is the vacuum permittivity,

is the electron (hole) concentration,

is the concentration of the filled electron (hole) trap state. Assuming a parabolic density of states (DOS) and Maxwell-Boltzmann statistics, the electron and hole concentrations are expressed as:

in

and

is the energy density of states of carriers in the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO),

and

is the energy level of LUMO and HOMO,

and

is the quasi Fermi level of electrons and holes,

is the Boltzmann constant and T is the device temperature. The existence of charge carrier traps in organic semiconductors is due to structural defects and/or impurities. Injected charge needs to first fill these traps before current flow can be established. This state is called trap limited current (TLC).^1,2 Exponential or Gaussian distributions are used to model trap distributions within organic semiconductors.³ In this work, a Gaussian distribution for the hole trap states is used:^{4 , 5}

in

is the total density of traps,

is the energy trap depth above the HOMO level, and

is the width of the distribution. The density of trapped holes was estimated by integrating the Gaussian density of states times the Fermi-Dirac distribution. Charge transport is controlled by drift in the electric field F and by diffusion due to charge density gradients. The steady-state continuity equations for electrons and holes in the drift-diffusion approximation are given by:

in

is the electron (hole) mobility,

is the electron (hole) diffusion constant, andR is the recombination rate. The charge carrier mobility is assumed to be field-dependent and has the Pool-Frenkel form:^6,7

in

is the zero-field mobility, and

It is the characteristic field of electrons (holes). High-energy chaos is not considered in this model, so we assume the validity of Einstein's relation to calculate the diffusion constant from the charge mobility. By the Langevin model⁸ gives the recombination rateR :

When electrons recombine with holes, they form excitons. The generated excitons can decay with the characteristic diffusion constant before radiative or nonradiative decayD _s migrate. The continuity equation for singlet excitons is given by:

inS is the exciton density. The first period is the singlet exciton production rate according to electron-hole recombination, which is 1/4, the second period represents the exciton diffusion, and the third period represents the decay constant with radiation

and the nonradiative decay constant

Exciton decay of , and the last period is expressed by having a field-dependent dissociation rate

The dissociation of excitons in the electric field is given by the Onsager-Braun model:^9,10

in

is the exciton radius,

is the exciton binding energy,

is a first-order Bessel function, and

is a field-related parameter. In this model, the impact of electric field quenching (EFQ) depends on the exciton binding energy

.2. Simulation results and comparison with experiment 2.1. Unipolar and bipolar reference devices Both hole-only and electronic-only devices were considered in order to test the electrical model, simulation parameters and charge carrier mobility before performing bipolar device simulations. The pure electronic device consists of a 190 nm BSBCz layer sandwiched between Cs (10 nm)/Al and 20 wt% Cs:BSBCz (10 nm)/ITO electrodes. By incorporating 10 nm MoO₃ Layer insertion between BSBCz (200 nm) and both ITO and Al results in a pure hole device. The bipolar OLED device contains the following structure: ITO/20 wt% Cs:BSBCz (10 nm)/BSBCz (190 nm)/MoO₃ (10 nm)/Al. The work function of the cathode (ITO/20 wt% Cs: BSBCz) is 2.6 eV, and the anode (MoO₃ /Al) has a work function of 5.7 eV. The energy level diagram of these device structures is shown in FIG. 48 . The reported charge carrier mobility (measured by time-of-flight) of BSBCz was used [11]. Figure 49a shows the measured reported mobilities of electrons and holes for BSBCz and the corresponding fits to the Pool-Frenkel field correlation model. The values of the fitted mobility parameters and other values of the input parameters required for the electrical simulations are shown in the table below. The hole and electron mobilities of BSBCz are about the same order of magnitude, indicating that BSBCz can transport both types of charge carriers. Table. Electrical simulation parameters

Experiments and simulations of monopolar and bipolar devicesJ ( V ) The curves are shown in Figure 49b. Experiments measured under direct current (DC) driveJ lower than18V , and higher than18V . The pure hole device current is largely controlled byV < 20 V Place trap restrictions. obtained by optimizing the simulated experimental data

,

and

The values are given in the table above. The results show good agreement between experiments and simulations for monopolar devices. For bipolar devices, the small deviation between measurements and simulations at lower current densities is due to the presence of experimental leakage currents. Simulation models predict similar current densities for hole-only and electron-only devices at high voltages, demonstrating a good electron and hole transport balance. Bipolar devices exhibit current densities an order of magnitude higher than unipolar current densities.2.2. bipolar DFB device The use of DFB grating resonators not only by amplifying light^{12 - 14} Providing positive optical feedback affects the optical properties of the organic laser and also affects the electrical properties of the organic laser. The effect of the nanostructured cathode on the electrical properties of the DFB OLED was calculated and compared to a reference OLED (without grating). The structure of DFB OLED is similar to bipolar OLED, the difference is that the nanostructured cathode is made of periodic grating SiO deposited on ITO₂ -Cs: BSBCz composition. The grating period is 280 nm and the grating depth is 60 nm, as represented in Figure 66a. In this structure, the thickness of BSBCz is 150 nm. For comparison, a reference OLED (ITO/20 wt% Cs:BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Al) without a grating. All parameters and conditions for bipolar devices have been retained since DFB and reference OLED have no additional fitting parameters. Experiment and simulation of DFB grating and reference OLEDJ ( V ) The curves are shown in Figure 66b. Electrical simulation predicts that at DC(V < 18V ) and pulsed operation (V ≥18V ) in both casesJ ( V ) The curves are in good agreement with the experimental results. removeJ ( V ) In addition to curve predictions, electrical simulations can access physical parameters that are difficult to determine experimentally, such as the spatial distribution of charge carrier densities, electric fields, and locations of recombination regions. First, we consider referring to OLED. Figures 67a-67b show the charge carrier distribution and electric field profile of the reference OLED at 10V and 70V. Free electrons are injected from the ITO/CS:BSBCz cathode into BSBCZ (atx = 0 μm ), and the free holes are from Al/MoO₃ Anode injection (x = 0 . 215 μm ). Due to carrier recombination, the carrier density decreases as it leaves the contact. whenno = p When , the electric field increases and reaches its maximum value at its center. At 10 V, the electric field is screened by the high charge carrier density close to the cathode and anode. At higher voltages (70V ), the electrons penetrate deeper and the electric field near the anode remains high. In the case of DFB grating OLED, at 70V Extract entity parameters below. Figures 68a-b show the spatial distribution of charge carrier densities n and p. Since the periodic nanostructured electrons of the cathode are not uniformly injected, their spatial distribution follows the periodic injection, as can be clearly seen in Figure 68b and Figure 68c. Holes are injected from a uniform anode and extend relatively uniformly in the bulk (Figure 68a, Figure 68c). When the hole reaches the cathode, it decays for the reference OLED (Fig. 67(b)). However, due to SiO₂ The presence of gratings, holes in SiO₂ The /BSBCz interface accumulates and exhibits high density (Fig. 68a). Figure 69a shows the periodic profile of the electric field, which is higher in the insulator and slightly modulated in the BSBCz layer. For a reference OLED (approximately 3.5×10⁶ V / cm ) remain the same strength. The current density profile shown in Figure 69b is modulated to a large extent and shown in SiO₂ /Cs: higher value near the BSBCz interface. To clarify SiO₂ /Cs: Reason for high current density values near BSBCz interface, recombination rate profileR Shown in Figure 70a. as we can see,R Periodic changes within the device are also shown. In the area delimited by the cathode/anode, the profile is identical to that of the reference OLED, whereas it is made of SiO₂ / decreases in the region delimited by the anode (see Figure 70c). In Cs:BSBCz/SiO₂ interface,R Shows a maximum due to hole and electron accumulation, as demonstrated in Figure 70d. The electric field inside the device is about MV/cm² , as shown in Figure 69a. Therefore, the exciton dissociation induced by the electric field is not negligible and largely affects the device performance. The singlet exciton binding energy of organic semiconductors ranges from 0.3 eV to 1.6 eV^{15 - 18} within the range. At low electric fields, the dominant deactivation processes are radiative decay and non-radiative decay. At high electric fields, the probability of exciton dissociation increases greatly and depends on the exciton binding energy. To account for electric field-induced exciton dissociation, the field-dependent dissociation rate given by Equation 10 is included in Equation 9 for singlet exciton continuity. Figure 71a shows the calculated exciton density for the reference deviceS , including those with different exciton binding energies _Eb (0 . 2 - 0 . 6 eV ) The EFQ. when _Eb When reduced, EFQ becomes a severe loss mechanism. Using molecules with high exciton binding energy requires overcoming EFQ. The exciton binding energy of BSBCz was estimated using the PL quenching yield experiment and its lower bound is0 . 6 eV . Figure 71b shows the results with and without electric field-induced exciton dissociation for the reference device and the DFB device.S ( J ) characteristic. In the absence of EFQ, S followsJ increase and display inJ = 3KA / cm ² 9×10 for DFB device¹⁷ cm ^{- 3} Relative to the 2×10 of the reference device¹⁷ cm ^{- 3} high value.S This difference in the device comes from different device architectures, which lead to differences in the device internalR distribution, as shown in Figures 70a, 70b. By considering the EFQ model and the BSBCz _Eb = 0 . 6 eV , the two devicesS increase, and untilJ = 0 . 5KA / cm ² It then decreases due to the electric field dissociation of the excitons. The EFQ in the DFB device was slightly lower than that in the reference device and may explain the experimentally low EQE roll-off of the DFB device compared to the reference device shown in Figure 47E. To gain further physical insight into the cause of EQE enhancement in DFB devices, the one-dimensional exciton distribution inside the reference device with or without EFQ is shown in Figure 72a. In the case of a DFB device, the two-dimensional exciton distributions without and with EFQ are shown in Fig. 72b, Fig. 72c, respectively. A comparison of the exciton density distribution (Fig. 73, bottom right) and the optical mode distribution in the device (Fig. 74, bottom) indicates that there is a large overlap between them at the 2nd grating region, contributing to optical amplification. This significant overlap certainly contributes to lower laser thresholds. In the reference device, in the absence of EFQ,S Disperse evenly. In the presence of EFQ, due to the high electric field (which reaches 3.5MV / cm ), in the blockS decrease (see Figure 79b). Close to the Cs:BSBCz/ITO interface, the electric field is lower, which avoids the EFQ of the excitons. In the case of the DFB device, excitons are generated from two recombination sites (site 1 and site 2), as shown in Figure 71a. close to SiO₂ The accumulation of charge on the grating creates a high exciton density (S =6×10¹⁷ cm ^{- 3} ) of the recombination region, named site 1. Site 2 has the same as the reference device (S =1×10¹⁷ cm ^{- 3} )identicalS . Without EFQ, the maximumS Provided by point 1, and explaining the high values in the DFB device compared to the reference device at low electric field (see Figure 71b). 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Phys. , vol. 143, no. 24, pp. 1-8, 2015.[ 6 ] Extremely low amplified spontaneous emission threshold and blue electroluminescence of spin-coated pure thin films of octopus Organic semiconductor lasers have been the subject of intensive research during the past two decades, leading to significant developments regarding laser threshold and operational device stability.^{1 - 3} These devices are currently being considered for a variety of applications including spectroscopic tools, data communication devices, medical diagnostics, and chemical sensors.^{1 - 5} However, there is currently no demonstration of electrically driven organic laser diodes and breakthroughs are still needed to develop true continuous wave optically pumped organic semiconductor laser technology.^1-3,6-8 The challenge of realizing electrically pumped organic laser diodes is well recognized and involves (i) additional absorption losses at the laser wavelength due to polaritons and long-lived triplet states, (ii) due to Singlet-triplet, singlet-polaron and singlet-thermal mutual destruction, quenching of singlet excitons, and (iii) stability of organic materials in operation of electroluminescent devices at high current densities. It should be noted that methods to reduce triplet and polaron loss have been proposed, including the use of triplet quenchers and reducing the active area of organic light emitting diodes (OLEDs) to spatially separate exciton formation from exciton decay area.^9,10 Although these issues need to be fully overcome and still require further research, it is also critical to substantially lower the threshold of amplified spontaneous emission (ASE) and lasing simultaneously in organic semiconductor thin films.³ To this end, there is a need for the development of novel high laser gain organic materials and improved resonator structures that can be incorporated into electrically pumped organic light emitting devices. Radiative decay rate ( _k ) is directly related to the Einstein B coefficient, as expressed by the following equation:

, where ν ₀ is the frequency of light,h is Planck's constant, andc is the speed of light. The ASE threshold is inversely proportional to the B coefficient, meaning a larger k_R Usually preferred to achieve a low ASE threshold.^{11 , 12} As outlined in a recently reviewed article on organic lasers,³ The lowest reported ASE threshold in small molecule-based organic thin films is 110 nJ/cm² , and obtained using 9,9'-spiroxane derivatives.¹³ at about 300 to 400 nJ/cm² Two other excellent organic semiconductor lasing materials exhibiting low ASE thresholds in thin films are 4,4'-bis[(N - carbazole) styryl] biphenyl (BSBCz) and sesternene derivatives.^12,14 Although the ASE threshold usually depends on the characteristics of the light source used for optical pumping, it is noteworthy that the ASE threshold mentioned above was determined by using a nitrogen-like laser for optical excitation. It is considered that the terpine derivatives are very promising for achieving a low ASE threshold, and some of these terpine derivatives exhibited higher than 1×10⁹ the s^{- 1} the rate of radiative decay.^{13 - 19} Significantly, previous work has specifically investigated the photophysical properties of trifentale, pentaflour and heptale derivatives functionalized with hexyl side chains.¹⁸ The results demonstrate that when the length of the oligomeric terpene molecule is increased, the rate of radiative decay increases and the ASE threshold decreases. In this case, it is crucial to verify whether the ASE/laser properties can be further improved by increasing the oligomer length. Here we report on stilbene derivatives showing no concentration quenching in spin-coated pure films with a PLQY of 87% and a fluorescence lifetime of about 600 ps. The chemical structure of this molecule is shown in Figure 75a. Large PLQY value and short PL lifetime of about 90 nJ/cm for the pure thin film of Baji² The threshold value of ASE reached an unprecedented level of ASE performance in organic non-aggregated gain media.³ The performance of organic disperse feedback (DFB) lasers and OLEDs based on pure thin films of stilbene provides further evidence that this fennel derivative is very promising for further work on organic semiconductor laser devices and their applications. The experimental procedures used in this work are described in the supplementary material.¹⁹ The absorption and steady-state PL spectra of pure thin films of octine spin-coated on fused silica substrates are shown in Figure 75b. The film is almost transparent in the visible range of wavelengths and exhibits a major absorption band with a maximum absorption peak wavelength of 375 nm in the ultraviolet radiation region. This absorption peak has previously been attributed to exciton coupling between terpine monomers.¹⁸ The light energy gap from the long wavelength absorption edge was calculated to be about 2.9 eV. The PL spectrum and image shown in inset 75b indicate that the pure thin film of Astragalus fluoresces blue. The spectrum shows a clear electronic vibrational structure with two peaks that can be assigned to the (0,0) and (0,1) transitions and a shoulder at longer wavelengths associated with the (0,2) transition. The maximum PL peak wavelength was found to be about 423 nm. In containing dispersed to 4,4'-bis(N - Absorption and steady-state PL spectra measured in spin-coated blends of 10 wt.% and 20 wt.% octilbene in the host of carbazolyl)-1,10-biphenyl (CBP) are shown in Figure 76 in (see Supplementary Material). The CBP host was chosen in this work because it is known that efficient Förster-type energy transfer occurs from CBP to most oligomeric terpene derivatives.¹⁴ Although the absorption spectrum of the blend is dominated by the CBP absorption, it can be seen that its PL spectrum is not significantly different from that of the pure film of octopus. PLQY and PL lifetimes were then measured in pure films and CBP blends. The 10 wt.% and 20 wt.% blends exhibited PLQY values of 88% and 87%, respectively, which are close to those found in pure films. Pure films and 10 wt.% and 20 wt.% blends also exhibit similar monoexponential fluorescence decays with characteristic PL lifetimes of 609, 570 and 611 ps, respectively (see Figure 77 in the supplementary material). This provides evidence that pure thin films of stilbene do not exhibit any PL concentration quenching, unlike that reported for similar triplet, pentactilbene, and heptaxene derivatives.¹⁸ Considering that about 1.7×10⁹ the s^{- 1} Due to the large radiation decay rate, this oligomeric terpene derivative can be expected to exhibit excellent ASE properties.^{11 , 12} The optical constants of the pure thin films of schibiflora were measured using variable angle ellipsometry and are shown in Figure 75c (calculation of optical constants from ellipsometry data can be found in Figure 78 in the Supplementary Material). The small optical anisotropy of the pure film indicates that the stilbene molecules are almost randomly oriented, which is consistent with previously reported ellipsometry results in the pure film of stilbene.²⁰ As schematically represented in Figure 79a, the ASE properties of octine pure films were characterized by optically pumping the sample at 337 nm with a nitrogen laser delivering 800 ps pulses at a repetition rate of 10 Hz. The excitation beam was focused into a stripe with a size of 0.5 cm × 0.08 cm, and the PL was collected from the edge of the organic thin film. Figure 79b shows the PL spectra measured from the edge of a 260 nm thick stilbene pure film at various pump intensities. A spectral line-narrowing effect is clearly seen at high excitation densities, accompanied by a full width at half maximum (FWHM) down to 5 nm, providing evidence that ASE occurred in this sample. Light amplification occurs at about 450 nm due to spontaneously emitted photons that are waveguided in the organic film and amplified by stimulated emission.^{twenty one} The ASE threshold was then determined from the plot of the output intensity emitted from the edge of the film versus the excitation intensity. The abrupt change in ramp efficiency seen in Figure 79c results in about 90 nJ/cm² ASE threshold value. It should be noted that the ASE properties were measured in pure thin films of stilbene with different film thicknesses in the range between 53 nm and 540 nm. The data presented in Figure 79d and Figure 80 (see Supplementary Information) indicate that the ASE threshold is lowest for films with a thickness of 260 nm. A similar thickness dependence of the ASE threshold has been reported in poly(9,9-dioctylfluorene) films.^{twenty two} This behavior is attributed to the interplay between the increase in mode confinement and the decrease in pump mode overlap as the thickness is increased. Significantly, the ASE threshold values measured in 260 nm thick schitilone pure films are lower than the lowest values ever reported in small molecule-based organic films.³ Such good performance should also mean that the octopus film exhibits extremely low loss coefficient values. For this purpose, the ASE intensity was measured according to the distance between the edge of the octopus film and the pumping strip. The results shown in Figure 81 (see Supplementary Information) resulted in a 5.1 cm^-1 loss factor. This low value is close to that of poly(9,9-dioctyl fluorene) film^{twenty three} The low values reported in , and provide evidence for the excellent optical waveguide properties of octopus films. It should be emphasized that, unlike most polyfennel systems, ostifera, as well as most fennel-based small molecules, are^{twenty four - 26} It does not exhibit any significant degradation of its photophysical properties under intense light exposure. In addition, the results shown in Figure 82 (see Supplementary Information) demonstrate that the pure thin films of octine exhibit excellent photostability at high pump intensities above the ASE threshold in both ambient and nitrogen atmospheres. This may be related to the high radiative decay rate of the film, which presumably leads to a reduction in photobleaching of the material under high intensity irradiation. Comparing the ASE threshold values measured in the shorter oligomeric fennel,^14,18 The results indicated that increasing oligomer length resulted in improved ASE performance. It should be noted, however, that preliminary experiments performed on stilbene films showed higher ASE threshold values than those obtained on stilbene films, indicating that stilbene derivatives are certainly organic semiconducting lasers in this series of oligomers. the most promising candidate. We then designed and fabricated a hybrid-order DFB grating structure consisting of a second-order Bragg scattering region surrounded by a first-order scattering region.¹⁷ This grating architecture is chosen to obtain a low laser threshold together with laser emission in a direction perpendicular to the substrate. In a DFB laser, the laser emits at the Bragg wavelength (lambda _Bragg ) occurs near , defined as:mλ _Bragg = 2no _eff Λ, whereno _eff is the effective refractive index of the laser gain medium,m is the Bragg order and L is the grating period.^1-3 Using the refractive index of the pure film of schibiflora as determined by ellipsometry (Fig. 75c) and the ASE wavelength measured in this study, form =1, 2, select the grating periods as 260 nm and 130 nm respectively. Figure 83a and Figure 83b show such DFB SiO₂ Schematic representation and scanning electron microscope (SEM) image of a grating fabricated using electron beam lithography and reactive ion etching techniques. It should be noted that the depth of the DFB grating is about 70 nm. To complete the laser device, a 260 nm thick thin film of octine was spin-coated on top of the DFB structure. Figure 83c shows the emission spectra detected perpendicular to the substrate plane at several excitation densities below and above the laser threshold. Below the threshold, a Bragg dip due to the optical stop band of the DFB grating can be observed. Above the laser threshold, a steep laser emission peak is clearly visible at the laser wavelength of about 452 nm. The output emission intensity and FWHM of this DFB laser as a function of excitation intensity are plotted in Fig. 81d. The FWHM of the laser emission peak was found to be below 0.3 nm at high excitation densities. At the same time, it was found that the laser threshold value judged by the change in the slope of the output intensity curve was about 84 nJ/cm² , which is slightly lower than the previously reported ASE threshold. Overall, the extremely low ASE and lasing threshold values measured in this work together with the excellent photostability of the films at high photoexcitation intensities demonstrate that this stilbene derivative is a promising candidate for lasing applications in organic semiconductors. gain medium material. To fully evaluate the potential of this stilbene derivative for use in organic laser diodes, it is also crucial to study the electroluminescent (EL) properties of this compound in pure thin films and in CBP blends using standard OLED structures. A schematic representation of the OLED fabricated in this study is provided in Figure 82a. The architecture of these devices is as follows: indium tin oxide (ITO) (100 nm)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (45 nm)/ EML (about 40 nm)/2,8-bis(diphenylphosphoryl)dibenzo[b,d]thiophene (PPT) (10 nm)/2,2',2''-(1,3 ,5-benzenetriyl)-paraffin(1-phenyl-1-H-benzimidazole) (TPBi) (55 nm)/LiF (1 nm)/Al (100 nm), where the emissive layer (EML) corresponds to In the pure film of Chinese succulent or the blend of Chinese succulent:CBP. In these devices, PEDOT:PSS functions as a hole injection layer, while PPT and TPBi serve as a hole blocking layer and an electron transport layer, respectively. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values of PEDOT:PSS, PPT and TPBi in Fig. 84a were taken from the literature.²⁰ The ionization potential of the pure thin film of octosine measured in air by photoelectron spectroscopy was 5.9 eV (see Figure 85 in the supplementary material). Using an optical bandgap value of 2.9 eV as determined from the absorption spectrum of pure thin films, the electron affinity of octopus can be estimated to be about 3 eV. As shown in Figure 86a (see Supplementary Information), in these OLEDs at 10 mA/cm² The EL spectra measured there were similar to the PL spectra measured in the pure thin films of cinnamon and in the CBP blend, indicating that the blue EL emitted from these devices came only from the cinnamon chromophore. Device current density-voltage-brightness (J -V -L ) Curves are shown in Figure 86b (see Supplementary Information). at 1 cd/m² where, OLEDs based on pure octopus thin films, 10 wt.% CBP blends and 20 wt.% CBP blends exhibited driving voltages of 5.0 V, 4.9 V and 4.5 V, respectively. The highest brightness value obtained in these OLEDs is 4580 cd/m for pure film² (at 12.6 V), 8520 cd/m for a 20 wt.% blend² (at 10.4 V), and 8370 cd/m for a 10 wt . % blend² (at 11.2 V). The external quantum efficiency of the device according to the current density (η_ext ) is plotted in Figure 84b. Its maximum value was found to be 3.9% for the pure film, 4.3% for the 20 wt.% blend, and 4.4% for the 10 wt.% blend. The difference in efficiency cannot be explained by the PLQY values of the three films, which are almost the same. In fact, a current research effort devoted to the molecular orientation of oligomeric stilbene molecules in spin-coated films demonstrates that although stilbene molecules are randomly oriented in pure films, 20 wt.% and 10 wt.% stilbene:CBP blends Relatively good horizontal orientation of the octine molecules was demonstrated.²⁶ Such horizontal molecular orientation of the emitting dipole should lead to an improvement in light extraction efficiency and thus may explain the slightly higher η measured in OLEDs based on CBP blends_ext value.^{20 , 26} In the case of organic laser diodes, the maximum η obtained in these OLEDs_ext Values are clearly promising. However, higher current densities should be injected into the device and above 100 mA/cm² Efficiency roll-off occurs at higher current densities, and this efficiency roll-off needs to be contained in additional work by improving the device architecture before this octopus derivative can be carefully considered as a candidate for an electrically driven organic laser device. In summary, this study demonstrates an unprecedented 90 nJ/cm² lower ASE threshold. Using a spin-coated pure film exhibiting a PLQY of 87% and a 1.7 × 10⁹ the s^{- 1} This achievement has been achieved by the derivatives of octopus with a large radiation decay rate. This blue light-emitting material is then used in low-threshold organic semiconductor DFB lasers and has an external quantum efficiency as high as 4.4% and a maximum luminance value close to 10,000 cd/m² In the fluorescent OLED. Overall, this study provides evidence that this stilbene derivative is an excellent organic material for organic semiconductor lasers. See Supplementary Material [URL to be inserted by AIP] for all information in the experimental procedures used for this study, absorption and fluorescence spectra of CBP blends in octopus thin films, ellipsometry data, additional ASE characterization results , and the determination of HOMO and LUMO.references 1. I. D. W. Samuel and G. A. Turnbull, Chem. Rev. 107, 1272 (2007). 2. S. Chénais and S. Forget, Polym. Int. 61, 390 (2012). 3. A. J. C. Kuehne and M. C. Gather, Chem. Rev. in press, DOI: 10.1021/acs.chemrev.6b00172. 4. Y. Wang, P. O. Morawska, A. L. Kanibolotsky, P. J. Skabara, G. A. Turnbull and I. D. W. Samuel, Laser & Photon. Rev. 7, L71-L76 (2013) 5. A. Rose, Z. G. Zhu, C. F. Madigan, T. M. Swager and V. Bulovic, Nature 434, 876 (2005). 6. I. D. W. Samuel, E. B. Namdas and G. A. Turnbull, Nature Photon. 3, 546 (2009). 7 . S. Z. Bisri, T. 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C 4, 11557 (2016).Experimental procedure photophysics and ASE Measure The stilbene derivatives were synthesized following the method disclosed in the previous literature.¹ Fused silica substrates were cleaned by ultrasonic treatment followed by ultraviolet radiation ozone treatment using detergent, pure water, acetone and isopropanol. Saccharomyces pure films and CBP: Sactilbene blended films were deposited on fused silica substrates by spin-coating from chloroform solutions in a nitrogen-filled glove box. It should be noted that the concentration of the solution and the spin speed were varied to control the thickness of the pure film of octopus. Absorption and steady-state emission spectra were measured using a UV-vis spectrophotometer (Perkin-Elmer Lambda 950-PKA) and a spectrofluorometer (Jasco FP-6500), respectively. PLQY in thin films was measured using a xenon lamp with an excitation wavelength of 340 nm and an integrating sphere (C11347-11 Quantaurus QY, Hamamatsu Photonics). PL decay was measured using a frame camera and a Ti-sapphire laser system (Millenia Prime, Spectra Physics) delivering optical pulses with a width of 10 ps and a wavelength of 365 nm. Variable angle ellipsometry (VASE) (J.A. Wollam, M-2000U) was performed by step 5° in 75 nm thick stilbene pure film at different angles from 45° to 75°. Then use analysis software (J.A. Woollam, WVASE32) to analyze the ellipsometry data to determine the anisotropic extinction coefficient and refractive index of the film. For the characterization of the ASE properties, the samples were optically pumped by a pulsed nitrogen laser (KEN2020, Usho) emitting at 337 nm. This laser delivered pulses with a pulse duration of 800 ps at a repetition rate of 10 Hz. Use a set of neutral density filters to vary the pump beam intensity. The pump beam was focused into a 0.5 cm × 0.08 cm stripe. Emission spectra from the edge of the organic thin film were collected using an optical fiber connected to a charge-coupled device spectrometer (PMA-11, Hamamatsu Photonics).organic DFB Manufacturing and Characterization of Lasers Clean 1 μm thick SiO with thermal growth following the same cleaning procedure as above₂ layers of silicon substrates. Hexamethyldisilazane (HMDS) was then spin-coated on SiO₂ on top of the surface and the samples were annealed at 120°C for 2 minutes. Thereafter, a 70 nm thick resist layer was spin-coated on the substrate from a ZEP520A-7 solution (ZEON Co.), and annealed at 180° C. for 4 minutes. Next, electron beam lithography was used to pattern the DFB grating on the resist layer using a JBX-5500SC system (JEOL). After electron beam irradiation, the pattern was developed in a developer solution (ZED-N50, ZEON Co.). In the following steps, the patterned resist layer acts as an etch mask. Using EIS-200ERT etching system (ELIONIX) by CHF₃ Plasma etches the substrate. Finally, using the FA-1EA etching system (SAMCO) by O₂ Plasma-etches the substrate to completely remove the resist layer. SEM (SU8000, Hitachi) was used to check the quality of DFB grating. To complete the organic laser device, finally a 260 nm thick thin film of octine pure was spin-coated from a chloroform solution on top of the DFB grating. For laser operation, the pulsed excitation light from a nitrogen laser (SRS, NL-100) is focused on the 6 × 10^{− 3} cm² on the area. The excitation wavelength is 337 nm, the pulse width is 3.5 ns, and the repetition rate is 20 Hz. The excitation light is incident on the device at approximately 20° relative to the normal to the plane of the device. The emitted light perpendicular to the surface of the device was collected using an optical fiber connected to a multi-channel spectrometer (PMA-50, Hamamatsu Photonics), which was placed at a distance of 6 cm from the device. Use a set of neutral density filters to control the excitation intensity.OLED Manufacture and Characterization OLEDs were fabricated by depositing organic layers and cathodes on pre-cleaned ITO glass substrates. The structure of the OLED fabricated in this study is as follows: ITO(100 nm)/PEDOT:PSS(45 nm)/EML(about 40 nm)/PPT(10 nm)/TPBi(55 nm)/LiF(1 nm)/ Al (100 nm), where the emissive layer (EML) corresponds to either a pure film of scallops or a blend of scallops:CBP. The PEDOT:PSS layer was spin-coated on ITO and annealed at 130°C for 30 minutes. The pure and blended films of octopus were spin-coated from chloroform solution on top of the PEDOT:PSS layer in a glove box environment. The thickness of the EML layer is typically about 40 nm. Next, a 10 nm thick layer of PPT and a 40 nm thick layer of TPBi were deposited by thermal evaporation. Finally, a cathode made of a thin LiF layer and a 100 nm thick Al layer was prepared by thermal evaporation through a shadow mask. The active area of the device is 4 mm² . Prior to characterization, the devices were encapsulated in a nitrogen atmosphere to prevent any degradation effects associated with oxygen and moisture. Under DC drive, use a power meter (Keithley2400, Keithley Instruments Inc.) and an absolute external quantum efficiency measurement system (C9920-12, Hamamatsu Photonics) to measure the current density-voltage-brightness (J -V -L )characteristic. EL spectra were measured using an optical fiber connected to a spectrometer (PMA-12, Hamamatsu Photonics).references 1. R. Anemian, J.C. Mulatier, C. Andraud, O. Stephan, J.C. Vial, Chem. Comm. 1608 (2002).[ 7 ] through CW amplified spontaneous emission ( ASE ) experiment Amplified spontaneous emission (ASE) experiments by CW were carried out in the dendrimers with double-core dendrimers and spin-coated pure thin films of scallops. Thin films were deposited onto pre-cleaned planar fused silica substrates without encapsulation. The film thickness is about 250 nm. To investigate the properties of the CW ASE, the thin film was optically pumped by a CW laser diode at 355 nm. Pulses with different widths were delivered using an acousto-optic modulator (AOM, Gooch & Housego) triggered with a pulse generator (WF 1974, NF Co.). The emitted light was collected from the edge of the film using a frame eye (C7700, Hamamatsu Photonics) with a temporal resolution of 100 ps connected to a digital video camera (C9300, Hamamatsu Photonics). Emission intensities were recorded using a photomultiplier tube (PMT) (C9525-02, Hamamatsu Photonics). Both the PMT response and the driving square wave signal were monitored on a multi-channel oscilloscope (Agilent Technologies, MSO6104A). In both materials, strip camera images and emission spectra at various pump intensities showed a clear line-narrowing effect above the threshold, attributable to stimulated emission and assignable to ASE. The ASE threshold was measured by comparing the output intensity of the excitation intensity curves for different pulse widths. The results show that the ASE threshold remains almost constant for varying pulse widths ranging from 100 μs to 5 ms. Furthermore, it can be noted that the ASE thresholds are in agreement with those measured in these materials using a pulsed nitrogen laser (pulse width of 800 ps and repetition rate of 10 Hz). The possibility of achieving CW lasing in both octose and biscathon dendrimers implies negligible triplet loss. This is in line with the fact that both materials exhibit extremely high photoluminescence quantum yields (PLQY) (92% PLQY in the double-core dendrimers and 82% PLQY in the pure thin films of octopus). In addition, transient absorbance measurements were performed in solutions of sucrose and biscarpus dendrimers to examine triplet-triplet absorption spectra. It can be seen that there is no overlap between the ASE and triplet absorption spectra, providing clear evidence that triplet absorption does not have any detrimental effect on CW lasing in both materials.[ 8 ] Current Injection into Organic Semiconductor Laser Diodes overview The laser diode is mainly based on inorganic semiconductors, but organic matter can also be an excellent gain medium through a unique manufacturing route. However, despite advances in optically pumping organic semiconductor lasers, electrically driven organic semiconductor laser diodes have not yet been achieved. Here we report the first demonstration of an organic semiconductor laser diode. Device-incorporated mixed-order dispersive feedback SiO in organic light-emitting diode structures₂ Raster and emit blue laser. These results demonstrate that laser injection of current directly into organic thin films can suppress the current density at high current densities by selecting high-gain organic semiconductors that do not exhibit triplet and polaron absorption losses at the laser wavelength and designing appropriate feedback structures. losses to be realized. This represents a first step towards simple organic-based laser diodes that could cover the visible and near-infrared spectrum and is a major advance towards future organic optoelectronic integrated circuits.A detailed description Due to the development of high-gain organic semiconductor materials and high-quality factor resonator structures^{1 - 5} Significant advances in the design of both have greatly improved the properties of optically pumped organic semiconductor lasers (OSLs) over the past two decades. Advantages of organic semiconductors as gain media for lasers include their high photoluminescence (PL) quantum yield, large stimulated emission cross section, and broad emission spectrum across the visible region as well as their chemical tunability and ease of processing. Recent advances in low-threshold decentralized feedback (DFB) OSLs demonstrate optical pumping of electrically driven nanosecond-pulsed phosphors, providing a path toward a new compact and low-cost visible laser technology⁶ the route. This type of miniaturized organic laser is very promising for lab-on-a-chip applications. However, the ultimate goal is to electrically drive organic semiconductor laser diodes (OSLDs). In addition to enabling full integration of organic photonic and optoelectronic circuits, the realization of OSLDs will open novel applications for high-performance displays, medical sensing, and biocompatible devices. The problems preventing the realization of lasing by direct electrical pumping of organic semiconductors are mainly due to optical losses from electrical contacts and occur at high current densities^4,5,7-9 The lower triplet state and polaron loss. Methods have been proposed to address these fundamental loss problems, including the use of triplet quenchers^{10 - 12} Contain triplet absorption loss and singlet quenching by singlet-triplet exciton mutual destruction, and reduce device active area¹³ This occurs by spatially separating exciton formation from exciton radiative decay and minimizing polaron quenching processes. However, even organic light-emitting diodes (OLEDs) and optically pumped organic semiconductor DFB lasers⁵ Progress has been made in, but current injection into OSLDs has not yet been conclusively demonstrated. Previous studies have suggested that if the additional losses associated with electrical pumping are fully contained¹⁴ , it needs to be higher than several kA/cm² The current density to achieve laser from OSLD. One of the most promising molecules to achieve OSLD is 4,4'-bis[(N - carbazole) styryl] biphenyl (BSBCz) (chemical structure in Figure 89a)¹⁵ , this is due to its excellent combination of optical and electrical properties (such as thin film (0.30 µJ cm under 800 ps pulse light excitation)^{− 2} )¹⁶ Moderately low Amplified Spontaneous Emission (ASE) threshold) and withstands 5 µs pulsed operation with better than 2%¹³ The maximum electroluminescent (EL) external quantum efficiency (n _EQE ) up to 2.8 kA cm in OLED^{− 2} The ability to inject current density. Furthermore, recently in optically pumped BSBCz-based DFB lasers¹⁷ demonstrated that lasing at a repetition rate of 80 MHz and under long-pulse light excitation of 30 ms is possible due to the minimal triplet absorption loss at the lasing wavelength of BSBCz thin films. Here we demonstrate beyond doubt the first example of lasing from organic semiconductor thin films based on mixed-order DFB SiO with integrated in the active area of the device₂ The BSBCz thin film in the grating reversed OLED structure was electrically directly actuated via the development and complete characterization of the OSLD. The architecture and fabrication of the OSLD developed in this study is schematically shown in Figure 89a and Figure 90 (see Materials and Methods for a detailed description of the experimental procedures). SiO on Indium Tin Oxide (ITO) Glass Substrate₂ The sputtered layer was sculpted by electron beam lithography and reactive ion etching to create a hybrid DFB grating with an area of 30 × 90 µm (Fig. 89b), and the organic layers and metal cathode were vacuum deposited on the substrate to complete the device. We design hybrid-order DFB gratings with first-order and second-order Bragg scattering regions, which provide strong optical feedback of laser emission and efficient vertical extraction, respectively^{17 , 18} . Based on Prague conditions^{4 , 19} ,mλ _Bragg =2no _eff Λ _m , select grating periods of 140 nm and 280 nm for the first-order and second-order regions respectively (Λ₁ and Λ₂ ),inm is the diffraction order,lambda _Bragg is the Bragg wavelength set to the wavelength of maximum reported gain (477 nm) for BSBCz, andno _eff is the effective refractive index of the gain medium, which is calculated for BSBCz^{20 , twenty one} is 1.70. The lengths of the individual first-order and second-order DFB grating regions in the characterized first assembly device are 1.12 µm and 1.68 µm, hereinafter referred to as OSLD. Scanning electron microscopy (SEM) images in Figures 89c and 89d confirm that the fabricated DFB gratings have periods of 140±5 nm and 280±5 nm, with a grating depth of about 65±5 nm. Complete removal of SiO in etched areas₂ layer to expose the ITO is critical for good electrical contact with the organic layer and was verified by energy dispersive X-ray spectroscopy (EDX) analysis (Fig. 90c, Fig. 9Od). Cross-sectional SEM and EDX images of intact OSLDs are shown in Figure 89d and Figure 89e. The surface morphology of all layers exhibited a grating structure with a surface-modulated depth of 50 nm to 60 nm. Although the interaction of the resonant laser mode with the electrode is expected to reduce the quality factor of the feedback structure, such a grating structure on the metal electrode should also reduce the device structure.^{twenty two , twenty three} Absorption loss in the mode of internal guidance. The OSLD fabricated in this work has a simple inverted OLED structure with energy levels ITO (100 nm)/20 wt.% Cs: BSBCz (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm), as shown in Figure 91a. Doping BSBCz films with Cs in the region close to the ITO contacts improves electron injection into the organic layer, and MoO₃ Used as a hole injection layer (Figure 92). Although the most efficient OLEDs generally use a multilayer architecture to balance charge^24,25 optimal, but at high current densities charges can accumulate at the organic heterointerface, which can affect device performance and stability²⁶ harmful. The OSLDs fabricated in this work contain only BSBCz as the organic semiconducting layer and are specifically designed to minimize the number of organic heterointerfaces. Also fabricated without SiO₂ A reference device for DFB gratings (hereinafter referred to as OLED) to study the effect of gratings on EL properties. Figure 91b shows optical microscope images of OSLD and reference OLED operated at 3.0 V direct current (DC). In addition to the previously described DFB gratings, five other DFB grating geometries (Table 1) were optimized and characterized in OSLD. While the EL emits uniformly from the active area of the reference OLED, a more drastic emission can be seen from the region of the second-order DFB grating in the OSLD, which is specifically designed to facilitate vertical light extraction (Fig. 91b and Fig. 93). Current density-voltage (J -V )andn _EQE -J The properties are shown in Figures 91c and 91d, and the properties obtained under DC conditions are shown in Figure 94. The active area used to calculate the current density of OSLD was estimated from SEM and laser microscope images. The maximum current density of the reference OLED before device breakdown is 6.6 A cm under DC operation^{− 2} Increased to 5.7 kA cm under pulsed operation^{− 2} , this is due to the pulse operation^13,27 Reduced joule plus. Under DC operation, the owner in the device exhibited a maximum of more than 2% at lower current densitiesn _EQE and above 1 A cm^{− 2} A strong efficiency roll-off was exhibited at a current density of 1, which was presumed to be due to thermal degradation of the device. On the other hand, the efficiency roll-off in OLEDs under pulsed operation (Fig. 91c, Fig. 91d) is above 110 A cm^{− 2} The current density starts at , and the previously reported¹³ match. Efficiency roll-off in OSLDs under pulsed operation was further suppressed, and it was even found thatn _EQE Substantial increase above 200 A cm^{− 2} To achieve the maximum value of 2.9%. Above 2.2 kA cm^{− 2} at current densityn _EQE The rapid decrease is likely due to thermal degradation of the device. Although the EL spectrum of OLED is similar to the steady-state PL spectrum of pure BSBCz film (Fig. 94c) and does not change with the change of current density, the EL spectrum of the glass surface from OSLD shows a spectrum with increasing current density under pulsed operation Line narrowing (Figure 95a). At 478.0 nm for below 650 A cm^{− 2} A Bragg dip corresponding to the stop band of the DFB grating was observed for the current density (Fig. 95b). When the current density was increased above this value, a strong spectral line narrowing occurred at 480.3 nm, indicating the onset of lasing. The intensity of the narrow emission peak was found to increase faster than the intensity of the EL emission background, which can be attributed to the nonlinearity associated with stimulated emission. The output intensity and full width at half maximum (FWHM) of the OSLD as a function of current is plotted in Figure 95c. Although the FWHM of the steady-state PL spectrum of pure BSBCz film is about 35 nm, the FWHM of OSLD decreases to a value below 0.2 nm at high current densities, which is close to our spectrometer (0.17 nm for the wavelength range of 57 nm) The spectral resolution limit. Ramp efficiency of output intensity varies abruptly with increasing current and can be used to determine 600 A cm^{− 2} (8.1 mA) threshold. At above 4.0 kA cm^{− 2} In the case of , the output intensity decreases with increasing current, presumably due to the strong increase in temperature causing the onset of device breakdown, but the emission spectrum remains extremely steep. This increase and subsequent decrease withn _EQE -J The curves match. The maximum output power measured by a power meter placed in front of the OSLD at a distance of 3 cm from the ITO glass substrate (Fig. 95d) was 3.3 kA cm^{− 2} at 0.50 mW. These observed EL properties largely indicate that optical amplification occurs at high current densities and that electrically driven lasing is achieved above the threshold current density. Beam polarization and shape characterized to provide further evidence that this is a laser⁹ . The output beam of the OSLD is largely linearly polarized along the grating pattern (Fig. 96a), which is expected for laser emission from a one-dimensional DFB. The spatial profile of the OSLD emission measured above the laser threshold at different current densities (Fig. 96b) shows the presence of well-defined Gaussian beams. Also, if this is the case the laser should have the appearance of a spot pattern, providing preliminary evidence of spatial coherence. Several phenomena which in the past have been misinterpreted as lasers must be excluded as observed states before we can claim lasers⁹ the cause. The emission of our OSLD is detected in the direction perpendicular to the substrate plane and shows a clear threshold state, so the line narrowing caused by the edge emission of the waveguide mode without laser amplification can be disregarded^20,28,29 . ASE can occur in a similar manner to lasers, but the FWHM in our OSLD (<0.2 nm) is much narrower than typical ASE linewidths for organic thin films (several nanometers), and comparable to optically pumped organic DFB lasers. Radiation (< 1 nm)⁵ The typical FWHM match. The extremely narrow emission spectrum obtained by inadvertently stimulating transitions in ITO was also misidentified as coming from the organic layer³⁰ launch. However, the peak emission wavelength of the OSLD in Figure 95a is 480.3 nm and cannot be attributed to emission from ITO, which has atomic spectral lines at 410.3 nm, 451.3 nm and 468.5 nm.³¹ If this is indeed the laser from the DFB structure, then the emission of the OSLD should be characteristic of the resonator mode, and the output should be very sensitive to any modification of the laser cavity. Accordingly, OSLDs (labeled OSLD-1 to OSLD-5 (Table 1)) with different DFB geometries were fabricated and characterized (Fig. laser^4,5,32,33 is very common. The laser peaks of OSLD, OSLD-1, OSLD-2, and OSLD-3 are almost identical (480.3 nm, 479.6 nm, 480.5 nm, and 478.5 nm, respectively), which have the same DFB grating period. In addition, OSLD-1, OSLD-2, and OSLD-3 owners had lower minimum FWHM (0.20 nm, 0.20 nm, and 0.21 nm, respectively) and well-defined thresholds (1.2 kA cm^{− 2} , 0.8 kA cm^{− 2} and 1.1 kA cm^{− 2} ). On the other hand, OSLD-4 and OSLD-5 with different DFB grating periods exhibit FWHM of 0.25 nm and 1.2 kA cm at 459.0 nm^{− 2} Threshold value (OSLD-4), and has a FWHM of 0.38 nm and 1.4 kA cm at 501.7 nm^{− 2} The laser peak of the threshold value (OSLD-5). These results clearly demonstrate that the laser wavelength is controlled by the DFB geometry. To verify that the lasing threshold of electrically driven OSLDs matches that obtained by optical pumping, a N₂ Laser (excitation wavelength of 337 nm) was used to measure the laser characteristics of an OSLD (OLSD-6) optically pumped through the ITO side (Figure 97). The laser peak of OLSD-6 under optical pumping (481 nm) coincides with that of OSLD under electrical pumping (480.3 nm). The laser threshold measured under optical pumping is about 430 W cm^{− 2} . Although this value is higher than that without the two electrode¹⁷ 30 W cm obtained in an optically pumped BSBCz-based DFB laser^{− 2} However, the thickness of the layers in this OSLD is optimized to minimize the optical loss caused by the presence of electrodes. Assuming no additional loss mechanism in OSLD-6 at high current density, 1.1 kA cm under electrical pumping^{− 2} The laser threshold value can be estimated according to the threshold value under optical pumping. This value is comparable to the threshold measured under electrical pumping in smaller devices with the same grating period (OSLD and OSLD-2) (0.6 to 0.8 kA cm^{− 2} ) are reasonably consistent. These results indicate that at high current densities³⁴ The additional losses normally occurring in OLEDs (including exciton mutual destruction, triplet and polaron absorption, quenching by high electric field, and Joule heating) have been almost contained in BSBCz OSLDs. This is in good agreement with the fact that EL efficiency roll-off is not observed in OSLDs under severe pulsed electrical excitation. Loss containment can be explained based on the BSBCz and the properties of the device. As mentioned previously, BSBCz thin films do not exhibit significant triplet loss³⁵ , and the reduction in device active area leads to Joule-assisted exciton quenching³⁶ decrease. In addition, based on the measurement of composite thin films BSBCz:MoO₃ and BSBCz: The overlap between the polaron absorption and emission spectra of Cs for both radical cations and radical anions in BSBCz is negligible (Figure 98). Electrical and optical simulations of the device were performed to further confirm that current injection lasing occurs in the OSLD (FIG. 99). Simulation of devices with and without gratings using carrier mobility extracted from fits of experimental data for unipolar devices (Fig. 99a, Fig. 99b)J -V The curves are in excellent agreement with the experimental properties (Fig. 99a, Fig. 99c, Fig. 99d), indicating sufficient etching for good electrical contact to devices with gratings. The recombination rate profiles (Fig. 99e, Fig. 99f) show periodic variations inside the device as electrons travel from the ITO electrode through the insulating SiO₂ Periodic injection of gratings. Similar to this recombination, the exciton density (Fig. 100a) spreads throughout the thickness of the organic layer, but is mainly concentrated in the SiO₂ In an area that does not obstruct the path from the cathode to the anode. The average exciton densities of OSLD and OLED (Fig. 99g) are similar, indicating close to SiO₂ The high accumulation compensation of the excitons results in a low exciton density between gratings (non-implanted regions) relative to a similar exciton density of the reference device. Calculated resonant wavelengths in OSLD for light extraction from second-order gratings and light trapping for waveguide loss in ITO layersl ₀ = Stimulated electric field distribution of the light field at 483 nmE. (x ,the y ) is clearly visible (Fig. 100b). The DFB resonator cavity is characterized by a confinement factor G of 40% and a quality factor of 255. The modal gain (g _m ) (which is an indicator of the magnification of the light in laser mode), with a reference to 2.8 10^{− 16} cm² BSBCz³⁵ stimulated emission cross sectionσ _Stimulate and is shown in Figure 100c for the second order region. Above 500 A cm^{− 2} The high modal gain and increasing modal gain are consistent with laser observations. existJ =500 A cm^{− 2} The area at which there is strong spatial overlap between the exciton density and the optical mode (Fig. 100d) corresponds to the area where both the exciton density and the optical field (Fig. 100a, 100b) are high. Thus, the DFB structure also helps to enhance localization and optical mode coupling via high exciton density in and above the valleys of the grating. In summary, this study demonstrates that through proper design and choice of resonator and organic semiconductor, it is possible to contain losses and enhance coupling from current-driven lasing of organic semiconductors. The lasing evidence here has been reproduced in multiple devices and has been fully characterized to rule out other phenomena that could be mistaken for lasing. The results fully support the claim that this is the first observation of an electrically pumped laser in an organic semiconductor. Low losses in BSBCz are integral to enabling lasing, so the development of strategies to design new lasing molecules with similar or improved properties is a crucial next step. This report opens up new opportunities in organic photonics and serves as the basis for future development of organic semiconductor laser diode technology that is simple, cheap and tunable and enables full and straightforward integration of organic-based optoelectronic platforms.Materials and methods Device manufacturing Indium tin oxide (ITO)-coated glass substrates were cleaned by ultrasonic treatment followed by UV ozone treatment using a neutral detergent, pure water, acetone and isopropanol (100 nm thick ITO, Atsugi Micro Co.) . 100 nm thick SiO₂ The layer (which will become the DFB grating) was sputtered onto the ITO coated glass substrate at 100°C. The argon pressure was 0.66 Pa during sputtering. The RF power was set at 100 W. The substrate was cleaned again by ultrasonic treatment followed by UV ozone treatment using isopropanol. SiO was treated with hexamethyldisilazane (HMDS) by spin coating at 4,000 rpm for 15 s₂ surface and annealed at 120°C for 120 s. A resist layer with a thickness of about 70 nm was spin-coated on the substrate from a ZEP520A-7 solution (ZEON Co.) at 4,000 rpm for 30 s, and baked at 180° C. for 240 s. Use a cm with 0.1 nC^{− 2} A dose-optimized JBX-5500SC system (JEOL) was used for electron beam lithography to draw the grating pattern on the resist layer. After electron beam irradiation, the pattern was developed in a developer solution (ZED-N50, ZEON Co.) at room temperature. The patterned resist layer was used as an etch mask while using the EIS-200ERT etch system (ELIONIX) with CHF₃ Plasma etches the substrate. To completely remove the resist layer from the substrate, use the FA-1EA Etching System (SAMCO) with O₂ Plasma etches the substrate. Etching conditions were optimized to completely remove SiO from recesses in DFB₂ Until ITO is exposed. Using SEM (SU8000, Hitachi) to observe the formation of SiO₂ Gratings on the surface (Fig. 89c). EDX (at 6.0 kV, SU8000, Hitachi) analysis was performed to confirm the complete removal of SiO from the spacing between DFBs₂ (Fig. 90c and Fig. 90d). Cross-section SEM and EDX were measured by Kobelco using cold field emission SEM (SU8200, Hitachi High-Technologies), energy dispersive X-ray spectrometry (XFlash FladQuad5060, Bruker) and focused ion beam system (FB-2100, Hitachi High-Technologies) (Fig. 89d, Fig. 89e). The DFB substrate was cleaned by conventional ultrasonic treatment. followed by the 1.5 × 10^{− 4} Thermal evaporation under the pressure of Pa in 0.1 nm s^{− 1} to 0.2 nm s^{− 1} The total evaporation rate of the organic layer and the metal electrode are placed on the substrate in vacuum to fabricate an indium tin oxide (ITO) (100 nm)/20 wt% BSBCz: Cs (60 nm)/BSBCz (150 nm)/MoO₃ (10 nm)/Ag (10 nm)/Al (90 nm) structure OSLD. SiO on ITO surface₂ layer acts as an insulator apart from the DFB grating. Therefore, the current region of the OLED is limited to the DFB region where the BSBCz is in direct contact with the ITO. A reference OLED with an active area of 30 × 45 µm was also fabricated using the same current field.Device Characterization All devices were encapsulated in a nitrogen-filled glove box using glass covers and UV-cured epoxy to prevent any degradation by moisture and oxygen. Using the integrating sphere system (A10094, Hamamatsu Photonics) to measure the current density-voltage-n _EQE (J-V-n _EQE ) characteristics (DC). For pulse measurements, a rectangular pulse with a pulse width of 400 ns, a pulse period of 1 µs, a repetition rate of 1 kHz, and a varying peak current was applied to the device using a pulse generator (NF, WF1945) at ambient temperature. Measured by amplifier (NF, HSA4101) and photomultiplier tube (PMT) (C9525-02, Hamamatsu Photonics) under pulse drivingJ -V - Brightness properties. Both the PMT response and the driving square wave signal were monitored on a multi-channel oscilloscope (Agilent Technologies, MSO6104A). Calculated by dividing the number of photons calculated from the PMT response EL intensity with a correction factor times the number of injected electrons calculated from the currentn _EQE . The output power was measured using a laser power meter (OPHIR Optronics Solution Company, StarLite 7Z01565). To measure the spectrum, the emitted laser light for the optically and electrically pumped OSLD was collected perpendicular to the surface of the device using an optical fiber connected to a multi-channel spectrometer (PMA-50, Hamamatsu Photonics) and placed at a distance of 3 cm from the device . The beam profile of the OSLD was checked by using a CCD camera (beam profiler WimCamD-LCM, DataRay). For the characteristics of OSLD-6 under optical pumping, nitrogen laser (NL100, N₂ laser, Stanford Research System), the pulsed excitation light is concentrated on the device's 6 × 10^{− 3} cm² in the area. The excitation wavelength was 337 nm, the pulse width was 3 ns, and the repetition rate was 20 Hz. The excitation light is incident on the device at approximately 20° relative to the normal to the plane of the device. Use a set of neutral density filters to control the excitation intensity. Steady-state PL spectral analysis was monitored using a spectrofluorometer (FP-6500, JASCO) in FIG. 98 and a spectrometer (PMA-50) in FIG. 94 .Device Modeling and Parameters Optical simulations of resonant DFB cavities were performed using Comsol Multiphysics 5.2a software. Solve the Helmholtz equation for each frequency in the RF module of Comsol software using the finite element method (FEM). Each layer is represented by its complex refractive index and thickness. The computational domain is bounded by a supercell consisting of a second-order grating surrounded by a first-order grating. A Froquet Periodic boundary condition is applied to the lateral boundary, and a Scattering boundary condition is used for the top and bottom domains. Only TE modes are considered, since TM modes are suppressed due to more losses (due to metal absorption) than TE modes. Charge transport through the OSLD was described using a two-dimensional time-independent drift-diffusion equation coupled with Poisson's equation and a continuity equation for charge carriers using Silvaco's Technical Computer Aided Design (TCAD) software. Electron and hole concentrations are expressed using parabolic density of states (DOS) and Maxwell-Boltzmann statistics. Gaussian distribution for modeling organic semiconductors³⁷ The distribution of traps inside. The charge carrier mobility is assumed to be field dependent and have the Pool-Frenkel form^{38 , 39} . High-energy chaos is not considered in this model, so we assume the validity of Einstein's relation to calculate the charge carrier diffusion constant from the charge mobility. By the Langevin model⁴⁰ gives the recombination rateR . Solve the continuity equation for singlet excitons by considering exciton diffusion, radiative and non-radiative processes. Experimental data of pure holes and pure electrons

, inL is the cavity length (2nd order grating region only) andd is the film thickness of the effect. Table 1 | Parameters of different OSLD geometries

Parameters of different grating geometries shown in Fig. 90 and total exposed ITO area used to calculate current densityA value. Table 2. Parameters for optical and electrical simulations.

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Figure 1. (a) Chemical structure of BSBCz and CBP, (b) Schematic of BSBCz:CBP film embedded in a second-order DFB structure , (c) Fabrication of DFB resonator structure by electron beam lithography and dry etching Schematic representation of the method, namely SEM images of the DFB structure at (d) 4500× magnification and (e) 120000× magnification, and (f) absorption and photoluminescence spectra of pure thin films of BSBCz and CBP. The DFB structure is directly engraved onto the silicon dioxide surface. When the second-order mode ( m = 2) is used for the Bragg equation ( mλ = 2 n _eff Λ ), the diffracted beam is emitted in a direction perpendicular to the film plane as shown in (b). The substantial overlap of CBP emission and BSBCz absorption enables efficient Förster-type energy transfer from CBP to BSBCz. In BSBCz:CBP blend films, CBP molecules are mainly excited by 337 nm light. Then, due to efficient energy transfer, the emission is from BSBCz, while no emission is observed from CBP. Figure 2. Emission as a function of excitation intensity for (a,c) BSBCz:CBP blended films and (b,d) BSBCz pure films embedded in DFB structures when excited with 0.8 ns wide pulses at 20 Hz Intensity and emission spectra and graphs of FWHM excitation. Insets in (a,b) show emission spectra measured near the laser threshold. Fig. 3. (a) is the frame camera image of laser oscillation and (b, c) are the temporal changes of laser intensity in BSBCz:CBP blended films. The repetition rate was changed from 0.01 MHz to 8 MHz. The excitation light intensity is fixed at about 0.44 μJ cm ⁻² , which is 1.8 times higher than Eth ₌ 0.25 μJ cm ⁻² . The time scale of (a, b) is 500 μs and the time scale of (c) is 2 μs. Fig. 4. (a): Graph of laser threshold as a function of repetition rate and (b): Operational stability of laser oscillations in organic DFB lasers based on BSBCz:CBP blend films and BSBCz pure films . To measure stability, the laser device was operated continuously quasi-cw at 8 MHz. The excitation light intensity was 1.5 times higher than the laser threshold. Figure 5. (a): The chemical structures of liquid carbazole (ECHz) hosts and escultyl derivatives. (b): Schematic representation of a liquid DFB laser fabricated using a first-order 1D grating pattern. (c): Image SEM of a PUA pattern with a period of 140 nm and a height of 100 nm. Scale bar represents 200 nm. (d): The emission spectrum of the nitrided and oxidized liquid DFB laser measured above the threshold at a repetition rate of 1 MHz. (e): Image of an oxidized blue liquid DFB laser operating in the quasi-cw state. Fig . 6. (a, b) are framed camera images of the laser emission and (c, d) are the temporal changes of the laser intensity in the nitrided and oxidized EHCz:Seventhyl DFB lasers. Repetition rate increased from 0.01 MHz to 4 MHz. The excitation light intensity was kept constant at 2.5 μJ cm ⁻² . Figure 7. The output emission intensity and full width at half maximum of the nitrided EHCz: Qilong DFB laser vary with the excitation intensity at different repetition rates. Figure 8. The output emission intensity and full width at half maximum in the oxidized EHCz: Qilong DFB laser vary with the excitation intensity at different repetition rates. Fig. 9. ( a) Lasing threshold of nitrided and oxidized liquid DFB organic semiconductor lasers as a function of repetition rate. (b) Photostability of oxidized and nitrided liquid organic semiconductor DFB lasers operated in the quasi-cw state at a repetition rate of 1 MHz. The excitation light intensity is 2.5 μJ cm ^{- 2} . Figure 10 . (a) Triplet-triplet absorption spectrum of oxidized and nitrogenated septame in chloroform solution. The triplet-triplet absorption disappears in the oxidized solution due to triplet quenching by molecular oxygen. Representative laser spectra measured in an oxidized DFB device are also shown. (b) Transient decay of triplet-triplet absorption specific gravity with time constant much higher than 1 ms. Figure 11 . Kinetics of photoluminescence intensity measured at 0.5 kW cm ⁻² for 4 different pulse durations varying from 50 to 800 μs in nitrided and oxidized EHCz:septacene blends. For this experiment, the gain medium was sandwiched between two identical flat fused silica substrates. The sample was then optically pumped by laser pulses from a cw HeCd laser emitting at 325 nm. The spot area is 2.0 × 10 ^{- 5} cm ² . The samples were illuminated in a direction perpendicular to the plane of the substrate and the PL intensity was measured at an angle of 45° using a photomultiplier tube. These results unequivocally demonstrate that oxygenation causes a suppression of STA loss due to triplet quenching by molecular oxygen. Figure 12. Manufacturing method of organic semiconductor DFB laser. It is a schematic representation of the method used to manufacture an organic DFB laser. Different sequential steps involved fabrication of DFB resonator structures by electron beam lithography, thermal evaporation of organic semiconductor films and spin-coating of CYTOP polymer films, followed by sealing of the device with a high thermal conductivity (TC) sapphire cap. Figure 13. Structure of a mixed-order DFB resonator. ( A ) Schematic representation of the mixed-order DFB grating structure used in this study. SEM images with ( B ) 2500× magnification and ( C ) 100000× magnification, and ( D ) SEM image of the device and (E) cross-sectional SEM of the device after deposition of 200 nm thick BSBCz:CBP blend film image. Figure 14. Lasing properties of an organic DFB laser in the quasi-CW state. Framed camera images showing laser oscillations from a representative BSBCz:CBP encapsulated hybrid-order DFB device at repetition rates from 0.01 MHz to 80 MHz with a period of ( A ) 500 µs or ( B ) 200 ns (only 80 MHz). The excitation intensity is fixed at about 0.5 µJ cm ^{− 2} , which is above the laser threshold ( E _th ). ( C ) Time evolution of laser output intensity at various repetition rates (f) in encapsulated BSBCz:CBP mixed-order DFB lasers. ( D ) Laser threshold as a function of repetition rate in several types of DFB devices. Lines guide the line of sight. Figure 15. Laser properties of an organic DFB laser in the long pulse regime. ( A ) Strip camera image showing integration within 100 pulses from an encapsulated mixed-order DFB device using BSBCz:CBP (20:80 wt.%) thin film as gain medium and by 30 ms and 2.0 kW cm ^-2 (top) or optically pumped laser emission with pulses of 800 µs and 200 W ^{cm -2 (} bottom). ( B ) Photograph of the DFB device operated in the long-pulse regime (30 ms excitation). ( C ) Laser threshold ( E _th ) as a function of excitation duration in various DFB devices. The dotted lines are the guides for the line of sight. ( D ) Laser output intensity from an organic DFB laser as a function of the number of incident pulses (100 µs, 200 W cm ^{− 2} ). Figure 16. Schematic representation of the geometry used for optical simulations. Fig. 17. Lasing threshold of mixed-order DFB laser based on BSBCz:CBP (6:94 wt.%) 200 nm thick film for different sizes of second-order gratings. The device was optically pumped by nitrogen laser delivering 800 ps pulses at a repetition rate of 20 Hz and a wavelength of 337 nm. Figure 18. (A) Absorption spectrum, (B) Steady-state photoluminescence spectrum and (C) Transient state of BSBCz:CBP ( 6:94 wt.%) films encapsulated with or without CYTOP film Photoluminescent decay. Figure 19. Various pump intensities below and above the laser threshold for representative organic mixed - order DFB lasers based on (A) BSBCz:CBP (6:94 wt.%) and (B) BSBCz pure thin films The emission spectrum below. The inset shows the emission spectrum near the laser threshold. Emission output intensity and FWHM as a function of pump intensity in (C) blended film and (D) pure film DFB laser. In these experiments, the organic film was covered by a spin-coated CYTOP film and a sapphire cap. The optical pump source was a nitrogen laser emitting 0.8 ns wide pulse excitation at a repetition rate of 20 Hz and a wavelength of 337 nm. Emissions from the laser device are collected in a direction perpendicular to the plane of the substrate. Figure 20. Emission output intensity and FWHM as a function of pump intensity at repetition rates of (A ) 0.01 MHz and (B) 80 MHz in a representative encapsulated blend mixed-order DFB laser. Figure 21. Laser threshold measured in the forward direction (increasing repetition rate) and reverse direction (decreasing repetition rate) as a function of repetition rate. The irreversible change of the lasing threshold is attributed to the degradation of the gain medium under intense light excitation. Figure 22. (A) Framed camera image and (B) corresponding emission spectra showing results from an unencapsulated 2-stage DFB device, an unencapsulated hybrid-stage DFB device , and an encapsulated hybrid-stage DFB device Emission at a repetition rate of 80 MHz and a pump intensity of 0.5 μJ cm ^{− 2} . Figure 23. (A) Operational stability of laser output oscillations from different organic DFB lasers based on BSBCz:CBP (6:94 wt . %) blend films. To measure stability, the laser device was continuously operated quasi-CW at 8 MHz or 80 MHz for 20 minutes. For each device, the excitation light intensity was 1.5 times its laser threshold. (B) Image of an encapsulated DFB-doped laser operating in the quasi-CW state at 80 MHz. Fig. 24. ( A) Output intensity of ASE centered at 472 nm as a function of pump energy and strip length in 200 nm thick BSBCz:CBP (20:80wt.%) film. Dashed lines were fitted to the data using equations reported in refs ( 7,8 ). From these fits the net gain of the waveguide is determined. (B) ASE intensity emitted from the edge of the waveguide film versus the distance between the pump strip and the edge of the blended film. The ASE properties of the films were studied using inorganic laser diodes emitting at 405 nm with different pulse widths (0.1, 10 and 50 μs). Figure 25. Encapsulated 20 wt.% blend mixed - order DFB mines measured at pump intensities of 200 W cm ^{− 2} and 2.0 kW cm ^{− 2} for long pulse durations of 800 µs and 30 ms, respectively The emission spectrum of the radiation. Figure 26. Strip camera image showing laser emission integrated within 100 pulses from an encapsulated mixed-order DFB device during a 30 ms long photoexcitation with a pump power of 2.0 kW cm ^-2 . The gain medium is BSBCz:CBP (20:80 wt.%). The excitation wavelength is 405 nm. To observe the laser during 30 ms using our frame camera system, the duty cycle percentage was changed to 2% to observe a 30 ms pulse in a 1 ms frame (0.02 × 30 ms = 0.6 ms). Figure 27. ( ^A ) Time evolution of laser output intensity , (B) measured ^encapsulated Emission spectrum of mixed-order DFB laser. (C) Stimulated emission and triplet absorption cross-section spectra of BSBCz. The emission spectrum of DFB laser measured from BSBCz pure film is higher than E _th . (D) Triplet absorption spectra were measured under Ar in solutions containing BSBCz. ( E ) Excitation power dependence of transient absorption spectra in solutions (BSBCz in dichloromethane and benzophenone in benzene). Figure 28. (A) Images showing the divergence of the emitted beam of the DFB laser near (B) and above (C) the threshold. The active gain medium is BSBCz:CBP (20:80 wt.%) film. Devices were pumped in the long pulse regime (10 ms excitation). Figure 29. (A) Emission spectrum as a function of polarization angle and (B ) emission intensity as a function of polarization angle. The device was based on a BSBCz:CBP (20:80 wt.%) blend and used a mixed-order DFB grating. The pump intensity was 200 W cm ^{− 2} and the pump pulse duration was 800 µs. It should be noted that 0 ^° corresponds to a direction parallel to the grooves of the DFB grating. Figure 30. Emission spectra and laser output intensity of the encapsulated mixed - order doping device as a function of pump intensity for long pulse excitation widths of (A, B) 1 µs and (C, D) 800 µs and FWHM. Figure 31. Strip camera image showing laser emission from a mixed-stage blended BSBCz:CBP (20:80 wt.%) DFB device encapsulated with (A ) sapphire or (B) glass cover. (C) Emission spectra of the glass-lid-encapsulated device for various pulse widths with a pump intensity of 2.0 kW cm ⁻² . The emission spectrum becomes broader with increasing pulse width, which can be explained by a significant increase in laser threshold with pulse width. For example, with pulse widths of 2 ms and 3 ms, the device operates below the laser threshold. (D) Laser threshold ( E _th ) measured as a function of excitation pulse width in DFB devices encapsulated with sapphire or glass cover. The dotted lines are the guides for the line of sight. Figure 32. Laser microscope images of unencapsulated admixture mixed - stage DFB lasers before (A) and (B) after irradiation by 100 excitation pulses with a width of 1 ms. The thickness profile in inset (B) shows the ablation of the organic film during high-intensity CW irradiation. The pump intensity is 200 W cm ⁻² . The framed camera images in (C) and (D) are shown from encapsulated and unencapsulated blends under the same irradiation conditions (1 ms pulse, pump intensity of 200 W cm ^{− 2} and 100 pulses integration of framed camera images) under launch. Figure 33. Scheme of DFB organic laser. Figure 34. (a) Scheme of 3 - layer thick block waveguide. (b) Effective refractive index ( n _eff ) of TE and TM modes as a function of film thickness d at laser wavelength 477 n. Figure 35. Numerically calculated reflectance spectra (solid lines) and Fano-profile fitted reflectance spectra (dashed lines) for different values of film thickness under normal incidence TE polarization. Figure 36. (a) Experimental laser emission spectra of fabricated laser devices with different _df . (b) Experimental laser wavelength and calculated resonance wavelength. Figure 37. (a) _Eth (square), Q factor extracted from numerical calculations ( Q _{FEM calculation} (triangle) and Fano fit QFano _fit (star)) and Γ (circle) as a function of d Graph of variation of _f , (b) Graph of experimental FWHM of laser emission and FWHM calculated from Fano resonance. Figure 38. Schematic representation of the geometry used for thermal simulations . Figure 39. Maximum temperature at the end of each pulse. Figure 40. Temperature rise in the gain region with time and for different pulse widths: (A) 1, (B) 10 , (C) 30 and (D) 40 ms. Figure 41. Temperature rise over time for a pulse width of 10 ms in encapsulated and unencapsulated devices. Figure 42. Temperature rise with time or number of pulses _{at tp} = 30 ms in the gain region. Figure 43. Schematic representation of the method for fabricating DFB gratings and organic laser diodes for electrically driving organic semiconductor DFB laser diodes. Different successive steps involved sputtering a 100 nm thick layer of _SiO2 on top of the patterned ITO electrodes, fabricating the DFB resonator structure in _SiO2 by electron beam lithography and dry etching, and thermally evaporating the organic semiconducting thin film and the top electrode. Figure 44. Schematic representation of the substrate after different steps of DFB fabrication on ITO. ( A ) patterned ITO, ( B ) after sputtering SiO ₂ onto ITO, ( C ) after fabricating DFB on ITO and ( D ) DFB structure. Figure 45. Schematic representation of the method for fabricating nanoimprinted DFB gratings. Different sequential steps involved the preparation of a 70 nm thick polymer layer on top of the patterned ITO electrodes, followed by fabrication of DFB resonator structures in the polymer by a simple nanoimprint lithography process at low cost. Figure 46. Structural characterization of a mixed - order DFB resonator for an organic laser diode. ( A ) Laser microscopy and ( B ) SEM images (with 5000× and 200000× (in inset) magnifications) of mixed-level DFB _SiO2 grating structures fabricated on top of ITO patterned glass substrates. ( C , D ) EDX and SEM analysis of mixed-order DFB gratings fabricated on top of ITO. These images confirm the exposure of the ITO for contact with the device. Figure 47. Structure and properties of electrically driven organic semiconductor DFB laser. ( A ) Schematic representation and energy potential diagram of an organic semiconductor laser diode. Micrographs of ( B ) organic DFB laser diode and ( C ) reference device (OLED without grating) with or without DC operation at 4 V. The device area is 140 × 200 μm. ( D ) Current density-voltage (JV) curves and ( E ) External quantum efficiency-current density (EQE-J) curves measured in a reference OLED device and an organic DFB laser diode under DC and pulsed operation. Figure 48. Diagram of energy levels for (a) pure electron device (b) pure hole device and (c) bipolar device. Figure 49. (a) Reported (symbols) and fitted (solid line) mobilities for the Pool-Frankel field - dependent model (solid line) for holes (blue) and electrons (red) for BSBCz. (b) Experimental (symbols) and simulated (solid lines) J ( V ) curves for a pure hole device (blue), a pure electron device (red) and a bipolar device (black). Figure 50. SEM ( A , B ) surface topography images and ( C , D ) cross-sectional images of laser diode structures after deposition of all layers. Figure 51. Schematic representation of some possible configurations of organic semiconductor laser diodes. DFB resonator structures (second-order and mixed-order gratings) can be ( A ) in _SiO2 by electron beam lithography and dry etching, ( B ) in ITO by electron beam lithography and dry etching, ( C ) by nano Nanoimprint lithography process in polymer on top of patterned ITO electrodes, or ( D ) fabricated by nanoimprint lithography on top of active layer. Figure 52. Schematic representation of an organic semiconductor laser diode with a two - dimensional DFB resonator structure (second-order and hybrid-order gratings) for 2D DFB lasers. Figure 53. Micrographs of ( A to D ) organic DFB laser diodes with or without DC operation at 4 V (A , the device in B is made with 36 A second-order periodic DFB structure was fabricated, and the device in D , C was prepared with a repeating structure with 4 second-order periods surrounded by 12 first-order periods). The device area is 30 × 101 μm. ( E ) Emission spectra of an electrically driven organic semiconductor DFB laser (the first-order and second-order grating periods of this device are 140 nm and 280 nm, respectively) collected perpendicular to the substrate plane for different injection current densities and ( F ) Varying output strength. Figure 54. Electroluminescence and PL spectra of BSBCz (black PL spectrum, red EL spectrum of the reference device, and blue EL spectrum with grating below laser threshold). Figure 55. Lasing properties of an electrically driven organic semiconductor DFB laser diode. ( A ) Emission spectra of an electrically driven organic semiconductor DFB laser (the first-order and second-order grating periods of this device are 140 nm and 280 nm, respectively) collected perpendicular to the substrate plane for different injection current densities and ( B ) its current-dependent The output strength of the density change. ( C ) Emission spectrum and ( D ) output intensity versus current density obtained in an organic DFB laser diode using a 1st grating period of 150 nm and a 2nd grating period of 300 nm, respectively. Figure 56. Lasing properties of an electrically driven organic semiconductor DFB laser diode. ( A ) Emission spectra of an electrically driven organic semiconductor DFB laser (the first-order and second-order grating periods of this device are 140 nm and 280 nm, respectively) collected perpendicular to the substrate plane for different injection current densities and ( B ) its current-dependent The output strength of the density change. Figure 57. ( A ) Current density-voltage (JV) curves with and without DFB. Devices with DFBs have a 1st order grating period of 150 nm and a 2nd order grating period of 300 nm, respectively. ( B ) External quantum efficiency versus current density in an electrically driven organic DFB solid-state laser without DFB at 500 ns pulses. Figure 58. SEM images ( A , B , C , D and E ) of mixed-order gratings with different numbers of periods in the first-order and second-order regions . ( F ) Table of mixed-order gratings with different numbers of periods in the first-order and second-order regions for designing DFBs. Figure 59. ( A ) Laser spectra of mixed -order gratings with different numbers of periods. The number of cycles at the top of each graph corresponds to the number of 2-order cycles and the number of 1-order cycles that can be seen in FIG. 58 . The bottom graph shows the output characteristics of the device. ( B ) Threshold energy of mixed-order grating lasers for different numbers of periods in the second-order region. In the case of optical pumping, the lowest threshold values were shown using 4 and 12 cycles in the first and second order regions, respectively. The optical pump source was a nitrogen laser emitting 0.8 ns wide pulse excitation at a repetition rate of 20 Hz and a wavelength of 337 nm. Emissions from the laser device are collected in a direction perpendicular to the plane of the substrate. Figure 60. ( A ) SEM images of mixed order gratings with 12 and 4 periods in the first and second order regions , respectively. ( B , C ) Organic DFB laser diodes with and without DC operation at 5 V. The device area is 2.9 × 10 μm. ( D ) Emission spectrum of reference OLED. Figure 61. ( A ) Schematic representation of the experimental setup used to examine the polarization of the laser. The EL spectrum of DFB laser diode ( B ) is lower than the laser threshold value (at 415 A cm ^{− 2} ) and ( C ) is higher than the laser threshold value (at 823 A cm ^{− 2} ) UL correlation and ( D ) reference (at 800 A cm ^{− 2} , without DFB), ( E ) EL intensity as a function of polarization angle. EL is polarized in the plane of the device (TE mode). Figure 62. ( A ) Schematic of OLED with DFB. ( B ) Microscope image of a DFB with a device area of 560 × 800 μm on an ITO substrate. ( C ) Optical pump output intensity as a function of excitation density for a DFB laser; excited by a CW laser at 405 nm. Figure 63. Micrographs of ( A , B ) organic DFB laser diode and ( C , D ) reference device (OLED without grating) with or without DC operation at 4 V. Figure 64. Laser microscope image of a circular mixed-order DFB grating structure fabricated using _SiO2 on an ITO patterned substrate. Figure 65. Microscope images of organic circular DFB lasers with and without actuation. Current density-voltage (JV) curves for devices with and without circular DFBs. External quantum efficiency versus current density in OLEDs with and without DFB. Figure 66. (a) Schematic representation of DFB grating OLEDs and (b) experimental (symbols) and simulated (solid lines) J ( V ) curves for DFB gratings and reference OLEDs. Figure 67. Spatial distribution of charge carrier density ( n , p ) and electric field F at (a) 10 V and (b) 70 V. Fig. 68 . (a) hole density p , (b) electron density n at 70 V , (c) n at y = 0.11 μm , plots of spatial distribution of p tangent through 2D part . Figure 69. Drawing of the profile of (a) electric field F and (b) current density J at 70 V. Figure 70. Plots of the cross-sectional recombination rate R for (a) the DFB device, (b) R for the reference device, (c ) the R tangent through the 2D part for the DFB device at y = 0.10 μm , and (d) at 70 V The n and p tangents of the DFB device pass through the 2D part when y = 0.164 μm . Figure 71. (a) S ( J ) characteristics of (a) without EFQ and with EFQ for different E _b for reference device and (b) for DFB device and reference device at E _b = 0.6eV S ( J ) characteristics. Figure 72. At 70 V , (a) Exciton distribution inside the EFQ and without EFQ reference device, (b ) Exciton distribution inside the DFB device without EFQ, (c) after EFQ Exciton distribution inside the DFB device. Figure 73. Exciton density distribution inside an unquenched DFB device (upper left), inside an EFB - passed DFB device (bottom left), and inside a PQ-passed DFB device ( Top right), Exciton density distribution inside the PQ and EFQ DFB device (bottom right). Figure 74. Optical density distribution inside the actual device Al/Ag/MoO ₃ /BSBCz/SiO ₂ /ITO in the DFB device (upper left) Air/BSBCz/SiO ₂ , (upper right) Air/BSBCz/SiO ₂ /ITO ( bottom) . Figure 75. (a) Chemical structures of stilbene derivatives. (b) Absorption and steady-state PL spectra measured in the spin-coated octine pure film at room temperature. The excitation wavelength of the measured PL spectrum is 376 nm. The images of pure thin films of octopus under UV illumination are shown in the inset. (c) Ordinary and extraordinary optical constants ( k and n ) of the pure thin films of schibiflora measured by variable-angle ellipsometry. The film thickness is about 75 nm. Figure 76. (a) Absorption and (b) steady-state PL spectra of blended films containing 10 and 20 wt . % stilbene in the CBP host. The excitation wavelength for the emission spectra of both films was 424 nm. Figure 77. Measured PL decay in pure films of stilbene and in blended films containing 10 and 20 wt.% of stilbene in the CBP host . The excitation wavelength is 365 nm. Figure 78. Experimental and simulated ellipsometric data ψ and Δ measured at different angles of incidence in spin-coated octopus pure films. Figure 79. (a) Schematic representation of experimental configurations used to characterize the ASE properties of organic thin films. (b) Emission spectra of a 260 nm-thick pure thin film of octopus collected from the edge of the organic layer for different excitation intensities below and above the ASE threshold. Steady-state PL spectra are also shown with dashed lines. The images of pure thin films of octopus under intense light irradiation are shown in the inset. (c) Output intensity as a function of excitation density from the edge of a 260 nm thick film (integrated at all wavelengths). (d) The ASE threshold value as a function of the thickness of the pure film of Asparagus chinensis. The excitation wavelength is 337 nm. Figure 80. Output intensity from the edge of the organic layer (integrated in all wavelengths) as a function of excitation density in several pure thin films of octogenin with various thicknesses in the range between 53 and 540 nm. These data were used to examine the thickness dependence of the ASE thresholds shown in Figure 2d. Figure 81 . ASE intensity plotted against the distance between the pump band and the edge of a 260 nm thick saccharine pure film. The solid line corresponds to the fit obtained from the mono-exponential decay function to determine the loss coefficient. Figure 82. Time decay of emission intensity above the ASE threshold from 260 nm thick stilbene pure films placed in air or nitrogen atmosphere. The pump intensity was 873 μJ/cm ² and 10 Hz. Figure 83. (a) Schematic representation of the experimental configuration used to characterize the properties of the octopus DFB laser. (b) SEM image of the mixed-order DFB grating used in this work. (c) Emission spectra of DFB lasers based on octine pure thin films collected perpendicular to the substrate plane for different excitation intensities below and above the laser threshold. (d) Output intensity of DFB laser as a function of excitation density. Figure 84. (a) Schematic representation of the OLED structure used in this study. HOMOs and LUMOs of organic materials for use in these devices are also provided. (b) External quantum efficiency versus current density in OLEDs based on octine pure and CBP blended films. Figure 85. Determination of the free potential of octopus in pure thin films using photoelectron spectroscopy in air . Taking into account the optical bandgap values determined from the absorption spectra of pure films, the electron affinity of octopus in pure films was then roughly estimated. It is important to note, however, that Koopman's theorem, which states that the vertical free potential is equal to the absolute value of the calculated HOMO energy, is not generally satisfied because of the relaxation process during the ionization process and electron association. Although the optical bandgap is generally different from the true electron gap, the electron affinity and LUMO can be roughly estimated from the difference between the free potential and the optical bandgap value. Fig. 86. ( a) EL spectra measured at a current density of 10 mA/cm ² and (b) J - V - L curves in OLEDs based on octine pure film and CBP blended film. Figure 87. CW ASE in pure thin films of octopus. Figure 88. CW ASE in pure thin films of octopus. Figure 89. Organic semiconductor DFB laser diode structure . a , Schematic representation of an organic laser diode. b , c , Laser microscope image ( b ) and SEM image ( c ) at 5,000× and 200,000× (inset) magnifications of the DFB SiO ₂ grating structure fabricated on top of ITO. d , Cross-sectional SEM image of a complete OSLD. e , Cross-sectional EDX image of OSLD. To improve the visibility of low-concentration Cs, enhance the contrast. Figure 90. Fabrication and structure of OSLD. a , Schematic diagram of the fabrication steps of OSLD. b , Structure of the ITO-coated glass substrate used in this study and the general structure of the DFB grating. Specific values of different grating parameters can be found in Table 1. c , d , EDX and SEM analysis of mixed-order DFB grating fabricated on top of ITO. These images confirm the possibility of making electrical contact with the ITO. Figure 91. Electrical properties of an electrically pumped organic semiconductor DFB laser. a , Energy level diagram of an OSLD with the highest occupied and lowest unoccupied molecular orbital levels indicated by the work function of organics and inorganics. b , Micrographs of the OSLD and the reference OLED under DC operation at 3.0 V. The lengths of the individual first-order grating regions and second-order grating regions are 1.68 µm and 1.12 µm. c , d , Current density-voltage ( J - V ) characteristics ( c ) and η _EQE - J characteristics ( d ) in OLED and OSLD under pulsed operation (pulse width of 400 ns and repetition rate of 1 kHz). Figure 92. Hole and electron transport in organic layers. a , b , Architectures of purely hole-based ( a ) and purely electronic ( b ) devices used to evaluate delivery. c , Representative current density-voltage in a pure hole device (HOD) and an pure electron device (EOD) under DC operation (filled symbols) and pulse operation (empty symbols) on logarithmic and linear (inset) scales ( J - V ) characteristics. The device area is 200 × 200 µm. These J - V curves indicate good transport of holes and electrons in the high voltage region in the laser diodes fabricated in this study. The electron current at lower voltages is higher than the hole current due to the trap limitation of the hole current. Figure 93. Properties of OSLDs with different DFB geometries . a , Micrograph of the OSLD operated at 3.0 V DC. b , c , d , current density-voltage ( J - V ) characteristics and η _EQE - J characteristics of OSLD. e , EL intensity and FWHM as a function of J. f , Emission spectrum as a function of J collected in the direction perpendicular to the plane of the substrate. Figure 94. DC characteristics and emission spectra of the device. a , b , current density-voltage ₍ J - V ) curve ( a ) and ηEQE - J curve ( b ) of OLED and OSLD measured under DC operation. c , PL spectrum of pure BSBCz film (black line) and EL spectrum of OLED (red line) and OSLD below laser threshold (blue line). Figure 95. Laser properties of OSLD. a , Emission spectra of OSLD collected in the direction perpendicular to the substrate plane for different injection current densities. b , Emission spectra near the laser threshold. c , Output intensity and FWHM as a function of current . d , output power as a function of current . The inset is a photograph of an OSLD under pulsed operation of 50V. Figure 96. Characterization of emission from OSLD. a , Emission spectra and emission intensities of OSLD measured at different polarization angles (inset). Here, 0 ^° corresponds to a direction parallel to the grooves of the DFB grating. b , CCD camera image showing the spatial Gaussian profiles of the emitted beam from the OSLD at different current densities. Figure 97. Characteristics of OSLD under optical pumping. a , Microscope image of a DFB grating used for optically pumped measurements. For other OSLDs (see Figure 89a), the same layer is deposited on the grating prior to measurement. b , Emission spectra of OSLD-6 collected in the direction perpendicular to the substrate plane under optical pumping with different optical excitation densities. The geometry of OSLD-6 is given in Table 1. c , Output intensity and FWHM of OSLD-6 as a function of optical excitation density. Excitation by _N2 laser was 3.0 ns at 337 nm and the device was at ambient temperature. Figure 98. Absorption spectra of radical cations and anions of BSBCz. In order to study the spectral overlap between components, the absorption spectra of pure thin film BSBCz (50 nm) and composite thin films BSBCz: MoO ₃ and BSBCz: Cs, (1:1 molar ratio, 50 nm) were measured. The differential absorption spectra of BSBCz cations and anions were calculated by subtracting the absorption spectra of pure films from those of _MoO3 -doped and Cs-doped films, respectively. An absorption spectrometer (Lamda 950, PerkinElmer) was used to measure the ultraviolet/visible/near-infrared absorption spectra of pure films and composite films. Also shown are the steady-state PL spectra of BSBCz pure thin films and representative laser emission spectra from BSBCz DFB lasers under optical pumping to demonstrate that polaron absorption in BSBCz OSLDs should be negligible. Figure 99. Optical and electrical simulations. a , Experimental (symbols) and simulated (solid lines) J - V curves for a purely hole device (blue circle), a purely electron device (red square) and a bipolar device (black triangle). Model parameters were extracted from Figure 92 by fitting to a unipolar device, and they were used to simulate a bipolar device. b , Comparison of mobilities calculated using parameters extracted from monopolar devices (solid lines) with reported ⁴¹ mobilities (symbols) for holes (blue) and electrons (red) in BSBCz. c , Experimental (symbols) and simulated (solid line) J - V curves of OSLD. d , Schematic illustration of the OSLD structure used for the calculation. e , Spatial distribution of recombination rate profile R of OSLD at J = 500 mA cm ^{− 2} . f , the section through (e) of the DFB device at y = 0.11 µm. g , the average exciton density of OSLD and OLED as a function of current density. Figure 100. Simulation of OSLD. a , Spatial distribution of exciton density S. b , Electric field distribution of a passive DFB resonator with a structure extended to include the first-order region at the resonant wavelength l ₀ =483 nm. c , Modal gain as a function of current density. d , Spatial overlap between the exciton density S (x,y) and the optical mode | E (x,y)| ² for one period in the second-order region at J = 500 A cm ^{− 2} . Layers other than the grating are modeled as flat (see Figure 99d), and y = 0 corresponds to the BSBCz/ _MoO interface.

Claims (54)

A current-excited organic semiconductor laser includes two electrodes, an organic optical gain layer and an optical resonator structure. The optical resonator structure has a DFB grating structure, and the grooves of the DFB grating structure are completely removed. The laser according to claim 1, wherein the organic optical gain layer is composed of at least one charge transport layer and at least one light amplification layer caused by stimulated emission. The laser according to claim 1 or 2, wherein at least one of the two electrodes is transparent. The laser according to claim 1 or 2, wherein the optical resonator structure is composed of a distributed feedback (DFB) structure. The laser according to claim 1 or 2, wherein the optical resonator structure is a one-dimensional resonator structure. A current-excited organic semiconductor laser comprising two electrodes, an organic optical gain layer and an optical resonator structure which is a one-dimensional resonator structure surrounded by second-order Bragg scattering by a first-order Bragg scattering region regional composition. The laser according to claim 1 or 2, wherein the optical resonator structure is a two-dimensional resonator structure. A current-excited organic semiconductor laser, which contains two electrodes, organic optical gain Layers and an optical resonator structure, the optical resonator structure is a two-dimensional resonator structure and is a circular resonator structure. The laser according to claim 1 or 2, wherein the optical resonator structure is composed of a distributed Bragg reflector (DBR) structure. The laser according to claim 1 or 2, which contains at least one hole transport or injection region and at least one electron transport or injection region. The laser according to claim 10, wherein the hole transport or injection region contains acceptors. The laser according to claim 10, wherein the hole transport or injection region is doped with acceptors. The laser according to claim 10, wherein the acceptor is a metal oxide. The laser according to claim 10, further comprising an accepting layer between the hole transport or injection region and the anode. The laser according to claim 10, wherein the electron transport or injection region contains a donor. The laser according to claim 15, wherein the electron transport or injection region is doped with a donor. Such as the laser of claim 10, which further contains the electron transport or injection region and the cathode between the donor layers. A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, and does not have an organic layer other than the organic optical gain layer. A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, and the optical resonator structure is an external optical resonator structure. A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, and the optical resonator structure is located between the two electrodes. A current-excited organic semiconductor laser includes two electrodes, an organic optical gain layer and an optical resonator structure, and further includes a current confinement structure between the two electrodes. A current-excited organic semiconductor laser includes two electrodes, an organic optical gain layer and an optical resonator structure, and the optical resonator structure is a whispering gallery type optical resonator structure. A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, wherein excitons are generated by current excitation and overlap with the optical resonant mode of the optical resonator structure. A current-excited organic semiconductor laser comprising two electrodes, an organic optical gain layer, and an optical resonator structure that exhibits no substantial exciton destruction at the laser wavelength. Such as the laser of claim 24, which does not exhibit substantial singlet-singlet and triplet-triplet mutual destruction. A current-excited organic semiconductor laser comprising two electrodes, an organic optical gain layer, and an optical resonator structure that exhibits no substantial polaron absorption loss at the laser wavelength. A current-excited organic semiconductor laser, which contains two electrodes, an organic optical gain layer and an optical resonator structure, and the ratio of electron mobility to hole mobility in the organic optical gain layer is 1/10 to 10/1 within the range. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the grooves of the DFB grating structure are completely removed. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the DFB grating structure is a mixed-order DFB grating structure in which a second-order Bragg scattering area is surrounded by a first-order scattering area. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the DFB grating structure is a mixed-order DFB grating structure in which a second-order Bragg scattering region and a first-order scattering region are formed. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and second-order Bragg scattering regions and first-order scattering regions are alternately formed. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the DFB grating structure has a circular structure. A laser having an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and there is no substantial spectral overlap between excited state absorption and laser emission. A laser with an organic layer on the DFB grating structure, wherein the organic layer contains an organic gain medium, and the stimulated emission cross section σ _em is 100 times or more than the triplet excited state cross section σ _TT , preferably 400 times larger Times or more than 400 times, more preferably 700 times or more than 700 times. A laser with an organic layer on the DFB grating structure, wherein the organic layer contains an organic gain medium, and the organic layer contains a host material and at least one dopant. A laser with an organic layer on the DFB grating structure, wherein the organic layer contains an organic gain medium, and the organic layer is directly or indirectly covered by sapphire. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the organic layer is directly or indirectly covered by a fluoropolymer. The laser according to claim 37, wherein the thickness of the fluoropolymer is less than 3 μm. The laser of claim 38, wherein the organic layer covered with fluoropolymer is further covered with sapphire. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, the DFB grating structure is a mixed-order DFB grating structure in which a second-order Bragg scattering region is surrounded by a first-order scattering region, and the laser is continuous wave laser. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, the DFB grating structure is a mixed-order DFB grating structure in which a second-order Bragg scattering region is surrounded by a first-order scattering region, and the laser is Quasi-continuous wave laser. A laser with an organic layer on the DFB grating structure, wherein the organic layer contains an organic gain medium, and the organic layer contains an organic compound with at least one stilbene unit. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the organic layer contains 4,4'-bis[( N -carbazole)styryl]biphenyl (BSBCz). The laser according to claim 43, wherein the organic layer contains 4,4'-bis[( N -carbazole) styryl]biphenyl (BSBCz) and 4,4'-bis( N -carbazolyl)- 1,1'-biphenyl (CBP). A laser with an organic layer on a DFB grating structure, wherein the organic layer contains organic A gain medium, and the organic layer contains a compound having at least one terpene unit. A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the thickness of the organic layer is 80-350nm, preferably 100-300nm, more preferably 150-250nm. The laser according to any one of claims 1, 2, 28-46, wherein the depth of the grating structure is less than 75nm, preferably 20-70nm. The laser according to any one of claims 1, 2, 28 to 46, wherein the grating structure is made of SiO ₂ . A laser with an organic layer on a DFB grating structure, wherein the organic layer contains an organic gain medium, and the laser does not contain a triplet quencher. A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, and the organic layer contains an organic compound with at least one stilbene unit. A current excitation type organic semiconductor laser, which contains two electrodes, an organic optical gain layer and an optical resonator structure, and the organic layer contains 4,4'-bis[( N -carbazole) styryl] biphenyl ( BSBCz). A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, and the organic layer contains a compound with at least one fennel unit. A current-excited organic semiconductor laser comprises two electrodes, an organic optical gain layer and an optical resonator structure, and the thickness of the organic layer is 80-350nm, preferably 100-300nm, more preferably 150-250nm. A current-excited organic semiconductor laser contains two electrodes, an organic optical gain layer and an optical resonator structure, and does not contain a triplet quencher.

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