CN108409636A - Structure, synthesis and application of dicarbazole micromolecule hole transport material - Google Patents

Abstract

The invention relates to a structure, synthesis and application of a bicarbazole micromolecule hole transport material, wherein a bicarbazole micromolecule hole transport material is designed and synthesized by introducing a dimethoxydiphenylamine group into an active site of 3,3',6,6' or 2,2',7,7' of N, N ' -bicarbazole. The material has low synthesis cost, good film forming property and high hole mobility, and can be used as an undoped hole transmission material to be applied to large-area perovskite solar cell devices to obtain higher device efficiency.

Description

Structure, synthesis and application of a bicarbazole-based small molecule hole transport material

technical field

The invention relates to the field of new materials for solar cells, in particular to the structure, synthesis and application of a bicarbazole-based small molecule hole transport material.

Background technique

After about five years of rapid development, the photoelectric conversion efficiency of organic-inorganic halide perovskite solar cells (PSCs) has exceeded 22%, which has potential commercial application prospects. In efficient conventional n-i-p-type PSCs, hole transport materials (HTMs) have been extensively studied as important interfacial layers between perovskite crystals and metal electrodes. HTMs play a very important role in promoting the extraction and transport of holes and inhibiting the recombination of carriers at the interface between perovskite and HTM, which can effectively improve the performance of devices. 2,2',7,7'-Tetrakis[N,N-bis(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD) is the earliest and most commonly used A class of organic HTMs applied to n-i-p-type PSCs can achieve high PCEs device applications. A series of small molecule and polymer HTMs comparable to Spiro-OMeTAD have been synthesized and reported successively, such as carbazole and thiophene HTMs, polytriarylamines (PTAAs), etc. However, most of the reported organic HTMs (including Spiro-OMeTAD) often need to be doped with additives such as 4-tert-butylpyridine (t-BP), organic lithium salt (Li-TFSI) and cobalt complexes due to their low charge mobility. To improve the device performance, these additives not only complicate the device fabrication process, but also have adverse effects on the stability and lifetime of PSCs. Therefore, the development of low-cost dopant-free HTMs is crucial to advance the future commercial application of PSCs technology.

Conjugated small molecule and polymer HTMs with DA-type structures with higher mobility have been developed as highly efficient non-doped HTMs. At present, the device efficiency of small-area PSCs (≤1cm ² ) based on DA-type undoped HTMs has reached as high as 19%. In order to better evaluate its practical application value, future research work will focus on applying dopant-free HTMs to large-area PSCs (≥1cm ² ). Since balancing high efficiency and low cost is the goal that large-area PSCs have been pursuing, the large-area PSCs based on doped-free HTMs also have high requirements for material cost and film-forming properties. However, most of the reported DA-type non-doped HTMs still require high-cost raw materials, multi-step synthesis routes, or complicated purification steps, which limit their application in large-area PSCs. It can be seen that it is necessary to further develop new strategies to design low-cost non-doped HTMs for high-performance large-area PSCs applications.

Recently, carbazole derivatives have been applied to PSCs as efficient and low-cost HTMs. It was recently reported that two carbazole units connected by “N-N” bond, the N,N′-bicarbazole unit with a structure similar to spirobifluorene, has not been used to construct HTMs for PSCs. In the present invention, the N,N'-bicarbazole group is used as the core center, and a kind of bicarbazole-based small molecule hole transport material is designed and synthesized, which can be used as non-doped HTMs in large-area PSCs.

Contents of the invention

Aiming at the above technical problems, the present invention uses N,N'-bicarbazole as the core, through the 3,3',6,6' or 2,2',7,7' activity of N,N'-bicarbazole A dimethoxydiphenylamine group was introduced at the site, and a bicarbazole-based small molecule hole transport material was designed and synthesized. The material of the invention has low synthesis cost, good film-forming property and high hole mobility, and can be used as a non-doped hole transport material to be applied to large-area perovskite solar cell devices to obtain higher device efficiency.

To achieve the above object, the technical solution provided by the invention is:

A bicarbazole small molecule hole transport material of the present invention has the following structural characteristics:

A method for preparing a bicarbazole-based small molecule hole transport material described in the present invention comprises the following steps:

(1) Synthesis of intermediate I or intermediate II: 3,6-dibromocarbazole or 2,7-dibromocarbazole was dissolved in acetone solution, and potassium permanganate was slowly added at room temperature. The obtained mixed solution was heated to reflux at 60° C., stirred and reacted at 65° C. for 5 hours, and then cooled to room temperature. Distilled under reduced pressure, washed with chloroform solution, extracted, filtered, washed with saturated sodium thiosulfate solution and saturated brine, dried over anhydrous magnesium sulfate, filtered, and distilled under reduced pressure. Recrystallization from chloroform/n-hexane gave intermediate I or intermediate II as a white powder.

(2) Synthesis of compound I or compound II: intermediate I or intermediate II with dimethoxydiphenylamine, tris(dibenzylideneacetone) dipalladium, tri-tert-butylphosphine tetrafluoroborate and tert-butanol Add potassium together to the toluene solution, under the protection of nitrogen, stir and heat to 110°C, react for 2h, then let stand and cool to room temperature, extract with saturated saline and dichloromethane, and then dry with anhydrous magnesium sulfate, Filtration and removal of the organic solvent gave the crude product, which was purified by column chromatography to obtain Compound I or Compound II.

The synthetic route is as follows:

The present invention also discloses the application of the bicarbazole-based small molecule hole transport material, which can be used as an undoped hole transport material for large-area perovskite solar cell devices (≥1cm ² ), wherein the device structure is FTO glass substrate/dense TiO ₂ layer/porous TiO ₂ layer/perovskite layer/hole transport layer/metal electrode, wherein the hole transport layer adopts the above-mentioned bicarbazole small molecule hole transport Material.

Compared with prior art, the beneficial effect of the present invention is:

(1) The bicarbazole small molecule hole transport material of the present invention has simple preparation process, readily available raw materials and low price, and is very suitable for industrial production.

(2) The bicarbazole-based small molecule hole transport material of the present invention has a higher glass transition temperature and better thermal stability, and can form a good amorphous film, which is beneficial to improving the environmental stability of solar cells.

(3) The bicarbazole-type small molecule hole transport material of the present invention can be applied in large-area perovskite solar cell devices without doping any additives, and the photoelectric conversion efficiency of large-area devices is higher than 17.5%, illustrating that the present invention The compound is a kind of hole-transporting material with excellent performance.

Description of drawings

The accompanying drawings are used to provide a further understanding of the present invention, and constitute a part of the description, and are used to explain the present invention together with the examples of the present invention, and do not constitute a limitation to the present invention.

Fig. 1 Cyclic voltammetry curves of compound I or compound II.

Figure 2 Hole transport properties of compound I or compound II.

Fig. 3 Structure of large-area perovskite solar cell devices made of compound I or compound II as hole transport materials.

Fig. 4 Device property diagram of large-area perovskite solar cells of compound I or compound II.

Detailed ways

The present invention will be further described below in conjunction with specific examples.

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Example 1

Preparation of Compound I;

The synthetic route is as follows:

(1) Synthesis of intermediate I: 3,6-dibromocarbazole (3.25 g, 10 mmol) was dissolved in 100 mL of acetone solution, and potassium permanganate (3.95 g, 25 mmol) was slowly added at room temperature. The obtained mixed solution was heated to reflux at 60° C., stirred and reacted at 65° C. for 5 hours, and then cooled to room temperature. Distilled under reduced pressure, washed with chloroform solution, extracted, filtered, washed with saturated sodium thiosulfate solution (15mL×2) and saturated brine, dried over anhydrous magnesium sulfate, filtered, and distilled under reduced pressure. Recrystallization from chloroform/n-hexane gave intermediate I (2.69 g, 83% yield) as a white powder. ¹ H NMR (500MHz, DMSO-d ₆ ) δ8.37 (d, J = 8.4Hz, 4H), 7.60 (dd, J = 8.4, 1.7Hz, 4H), 7.20 (d, J = 1.7Hz, 4H) . ¹³ C NMR (126 MHz, DMSO) δ 140.55, 125.66, 123.78, 121.02, 120.71, 111.88.

(2) Synthesis of Compound I: Intermediate I (1.30g, 2mmol) was mixed with dimethoxydiphenylamine (2.02g, 8.8mmol), tris(dibenzylideneacetone)dipalladium (73mg, 0.08mmol), Add tri-tert-butylphosphine tetrafluoroborate (35mg, 0.12mmol) and potassium tert-butoxide (1.35g, 12mmol) into 50mL of toluene solution, under the protection of nitrogen, heat to 110°C while stirring, and react for 2h , and then cooled to room temperature, extracted with saturated brine and dichloromethane, dried with anhydrous magnesium sulfate, filtered, and removed the organic solvent to obtain a crude product, which was purified by chromatographic column operation to obtain compound I (2.12 g, 85% yield). ¹ H NMR (500MHz, DMSO-d ₆ ) δ7.73 (d, J=8.5Hz, 4H), 6.93–6.89 (m, 16H), 6.82–6.78 (m, 16H), 6.68 (dd, J=8.5 ,2.1Hz,4H),6.18(d,J＝2.0Hz,4H),3.69(s,24H) ^.13 CNMR(126MHz,DMSO)δ155.99,147.13,141.29,140.76,126.54,121.12,115.94,115.68,115.21 ,99.90,55.63.MS:m/z(%):[M] ⁺ calcd for C ₈₀ H ₆₈ N ₆ O ₈ :1240.51;found:1240.47.Elemental Analysis:C,77.40;H,5.52;N,6.77; O, 10.31. Found: C, 77.57; H, 5.29; N, 6.81; O, 10.44.

Example 2

Preparation of Compound II;

The synthetic route is as follows:

(1) Synthesis of intermediate II: 2,7-dibromocarbazole (3.25 g, 10 mmol) was dissolved in 100 mL of acetone solution, and potassium permanganate (3.95 g, 25 mmol) was slowly added at room temperature. The obtained mixed solution was heated to reflux at 60° C., stirred and reacted at 65° C. for 5 hours, and then cooled to room temperature. Distilled under reduced pressure, washed with chloroform solution, extracted, filtered, washed with saturated sodium thiosulfate solution (15mL×2) and saturated brine respectively, dried over anhydrous magnesium sulfate, filtered, and distilled under reduced pressure. Recrystallization from chloroform/n-hexane gave intermediate II (2.46 g, 76% yield) as a white powder. ¹ H NMR (500MHz, DMSO-d ₆ ) δ8.74 (d, J=1.9Hz, 4H), 7.56 (dd, J=8.7, 2.0Hz, 4H), 6.91 (d, J=8.5Hz, 4H) . ¹³ CNMR (126MHz, DMSO) δ 138.31, 130.22, 124.48, 122.53, 114.14, 110.82.

(2) Synthesis of Compound II: Intermediate II (1.30g, 2mmol) was mixed with dimethoxydiphenylamine (2.02g, 8.8mmol), tris(dibenzylideneacetone) dipalladium (73mg, 0.08mmol), Add tri-tert-butylphosphine tetrafluoroborate (35mg, 0.12mmol) and potassium tert-butoxide (1.35g, 12mmol) into 50mL of toluene solution, under the protection of nitrogen, heat to 110°C while stirring, and react for 2h , and then left to cool to room temperature, extracted with saturated brine and dichloromethane, dried with anhydrous magnesium sulfate, filtered, and removed the organic solvent to obtain a crude product, which was separated and purified by chromatography to obtain compound II (1.97 g, 79% yield). ¹ H NMR (500MHz, DMSO-d ₆ ) δ7.65 (d, J=2.4Hz, 4H), 7.43 (d, J=8.7Hz, 4H), 7.09 (dd, J=8.6, 2.3Hz, 4H) ,6.88(d,J=9.4Hz,16H),6.81(d,J=9.5Hz,16H),3.70(s,24H). ¹³ C NMR(126MHz,DMSO)δ154.61,142.73,140.23,137.63,124.96, 124.09, 123.61, 117.40, 115.10, 112.45, 55.66.MS: m/z(%): [M] ⁺ calcd for C ₈₀ H ₆₈ N ₆ O ₈ : 1240.51; found: 1240.89.C ₈₀ H ₆₈ N ₆ O ₈ Elemental analysis of: C, 77.40; H, 5.52; N, 6.77; O, 10.31. Found: C, 77.20; H, 5.63; N, 6.48; O, 10.52.

Example 3

Performance characterization of compound Ⅰ and compound Ⅱ;

(1) Determination of photophysical properties;

Toluene solutions of compound I and compound II were prepared, and thin films of compounds were prepared using a KW-4A spin coater developed by the Institute of Microelectronics, Chinese Academy of Sciences. The absorption and emission spectra of the compound films were measured by Shimadzu UV-1750 ultraviolet-visible spectrometer and Hitachi F-4600 fluorescence spectrometer. It is measured that the absorption peaks of compound Ⅰ in the film state are located at 301nm and 377nm, the absorption band edge is 441nm, the optical band gap is 2.81eV, and the maximum emission peak is located at 462nm; while the absorption peaks of compound Ⅱ are located at 306nm and 386nm, the maximum absorption edge It is 426nm, the optical bandgap is 2.91eV, and the maximum emission peak is located at 433nm.

(2) Determination of electrochemical properties;

The electrochemical properties of the compound were determined by electrochemical cyclic voltammetry (CV). The experimental instrument was Chenhua CHI660E electrochemical workstation, which used a three-electrode system, including glassy carbon working electrode, Ag/AgCl reference electrode and a platinum wire counter electrode. The solvent used in the determination is generally dry dichloromethane, the electrolyte is tetrabutylammonium hexafluorophosphorus (Bu ₄ NPF ₆ ), and the concentration is 0.1M; the test environment needs nitrogen protection. The scanning rate of the instrument is 0.1V/s, the reference substance is ferrocene (FOC), and the HOMO energy level of the material is calculated by measuring the starting voltage of the oxidation process. The measured HOMO levels of compound Ⅰ and compound Ⅱ are -5.11eV and -5.15eV, respectively.

(3) Determination of thermodynamic stability;

Differential scanning (DSC) test: The DSC spectrum was tested on a Shimadzu DSC-60A differential calorimeter. Under the condition of nitrogen protection, the sample was first heated to a state below the decomposition temperature at a rate of 10°C/min, and then, under the condition of liquid nitrogen Lower the temperature back to the initial temperature, and then scan again at a rate of 10°C/min for the second time.

Thermogravimetric (TGA) test: The TGA spectrum was tested on a Shimadzu DTG-60H thermogravimetric instrument. Under the condition of nitrogen protection, the heating rate was 10°C/min, and the flow rate of nitrogen gas in the protective airflow was 20cm ³ /min. The weight of the material changed until reach constant weight.

Through DSC and TGA tests, the glass transition temperatures of compound I and compound II are 100 ^o C and 145 °C, respectively, and the 5% thermal weight loss temperatures are 397 °C and 442 °C.

(4) Determination of charge mobility;

The hole mobilities of the compounds are measured by space charge limited current method (SCLC), and the mobilities of compound I and compound II are 1.13×10 ^-4 cm ² V ^-1 S ^-1 and 0.95×10 ^-4 cm ² respectively V ^-1 S ^-1 .

Example 4

Compound Ⅰ and compound Ⅱ are used as hole transport materials in large-area perovskite solar cell devices;

A large-area perovskite solar cell device prepared by using compound I and compound II described in the present invention as a hole transport layer, including: FTO glass substrate, dense _TiO2 layer, porous _TiO2 layer, perovskite layer, hole Transport layer and metal electrode, wherein, FTO glass substrate is composed of glass substrate and FTO cathode (fluorine-doped tin oxide glass electrode), dense _TiO2 layer and porous _TiO2 layer as _TiO2 electron transport layer, perovskite layer as light absorbing layer.

The preparation steps of the large-area perovskite solar cell device:

(1) Cleaning: first clean the dust and other pollutants attached to the surface of the FTO glass substrate with detergent, then use 15mL of 1% surfactant solution, water and ethanol to ultrasonically remove organic pollutants, and the cleaned FTO Dry the glass substrate with nitrogen to obtain the transparent conductive substrate with a clean surface required for the experiment, and then treat it with ultraviolet rays-ozone for 30 minutes to ensure that the surface is clean and clean;

(2) Preparation of dense TiO ₂ layer: At 500 ° C, the butanol solution of bis(acetylacetonyl) diisopropyl titanate was deposited on a clean FTO glass substrate by spray pyrolysis, and after cooling to room temperature , the obtained TiO ₂ /FTO substrate was cut into pieces with a size of 2.5cm×2.5cm;

(3) Preparation of porous TiO ₂ layer: spin-coat a suspension made of TiO ₂ slurry and ethanol (1:6, m/m) on the TiO ₂ /FTO substrate obtained above, and then dry at 100°C for 10 min. Then burn at 500°C for 30min to form a porous _TiO2 layer;

(4) Preparation of perovskite layer: FAI (1M), PbI ₂ (1.1M), MABr (0.2M) and PbBr ₂ (0.22M), CsI (0.065M) mixed in DMF:DMSO=4:1(v The 1.32M Cs _0.05 FA _0.79 MA _0.16 PbI _2.49 Br _0.51 precursor solution obtained in :v) was used to prepare the perovskite layer by two-step spin-coating steps at 1000rpm for 10s and 6000rpm for 20s. The chlorobenzene anti-solvent was added dropwise in the last 5 s of the second spin-coating process. Subsequently, the substrate was dried at 100° C. for 1 h to obtain the desired perovskite layer.

(5) Preparation of the hole transport layer: prepare a pentachloroethane solution with a concentration of 15 mg/mL of Compound I or Compound II, and then spin-coat the prepared solution at a speed of 3000 rpm for 30 seconds to deposit on the perovskite layer;

(6) Place it in a vacuum evaporation chamber, and evaporate the metal electrode onto the surface of the hole transport layer by a vacuum evaporation method to prepare a perovskite solar cell device.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention in any form. Any skilled person who is familiar with the profession, without departing from the scope of the technical solutions of the present invention, according to the technical essence of the present invention, Any simple modifications, equivalent replacements and improvements made in the above embodiments still fall within the protection scope of the technical solution of the present invention.

Claims (6)

1. A bicarbazole small molecule hole transport material, characterized in that: the chemical structural formula is as follows: 2. The preparation method of the bicarbazole class small molecule hole transport material according to claim 1, characterized in that: comprising the following steps: (1) Synthesis of intermediate I or intermediate II: dissolve 3,6-dibromocarbazole or 2,7-dibromocarbazole in acetone solution, slowly add potassium permanganate at room temperature; will obtain The mixed solution was heated to reflux at 60°C, stirred and reacted at 65°C for 5 hours, then cooled to room temperature; distilled under reduced pressure, washed with chloroform solution, extracted, filtered, and washed with saturated sodium thiosulfate solution and saturated brine respectively , dried over anhydrous magnesium sulfate, filtered, and distilled under reduced pressure; recrystallized with chloroform/n-hexane to obtain intermediate I or intermediate II as a white powder; (2) Synthesis of compound I or compound II: intermediate I or intermediate II with dimethoxydiphenylamine, tris(dibenzylideneacetone) dipalladium, tri-tert-butylphosphine tetrafluoroborate and tert-butanol Potassium was added to the toluene solution together, under the protection of nitrogen, heated to 110 ° C while stirring, reacted for 2 hours, then stood and cooled to room temperature, extracted with saturated saline and dichloromethane, and dried with anhydrous magnesium sulfate. Filter and remove the organic solvent to obtain the crude product, which is purified by chromatographic column to obtain compound I or compound II; The synthetic route is as follows: 3. the application of the described bicarbazole class small molecule hole transport material of claim 1, it is characterized in that: this class material can be applied to large-area perovskite solar cell device (≥ 1cm ² ), wherein the device structure is FTO glass substrate/tight _TiO2 layer/porous _TiO2 layer/perovskite layer/hole transport layer/metal electrode, wherein the hole transport layer adopts the bicarbazole described in claim 1 Small molecule-like hole transport materials. 4. adopt the method for preparing the large-area perovskite solar cell device by the bicarbazole class small molecule hole transport material according to claim 1, it is characterized in that: comprise the following steps: 1) Cleaning: first clean the dust and other pollutants attached to the surface of the FTO glass substrate with detergent, then use 15mL of 1% surfactant solution, water and ethanol to ultrasonically remove organic pollutants, and the cleaned FTO glass The substrate is blown dry with nitrogen to obtain a transparent conductive substrate with a clean surface, and then treated with ultraviolet-ozone for 30 minutes to ensure that the surface is clean and clean; 2) Preparation of dense TiO ₂ layer: At 500 °C, the butanol solution of bis(acetylacetonato)diisopropyl titanate was deposited on a clean FTO glass substrate by spray pyrolysis, and after cooling to room temperature, Obtain TiO ₂ /FTO substrate; 3) Preparation of porous TiO ₂ layer: Spin-coat a suspension made of TiO ₂ slurry and ethanol on the TiO ₂ /FTO substrate obtained above, then dry at 100°C for 10min, and burn at 500°C for 30min to form a porous layer. ₂ layers of TiO; 4) Preparation of perovskite layer: 1.32M Cs _0.05 FA _0.79 MA _0.16 PbI _2.49 Br _0.51 precursor solution obtained by mixing FAI, PbI ₂ , MABr, PbBr ₂ , and CsI in DMF:DMSO=4:1 (v:v) , the perovskite layer was prepared by two-step spin-coating steps, the two-step spin-coating was rotated at 1000rpm for 10s and 6000rpm for 20s, and chlorobenzene anti-solvent was added dropwise in the last 5s of the second spin-coating process; subsequently, the base The sheet was dried at 100°C for 1 hour to obtain the required perovskite layer; 5) Preparation of the hole transport layer: preparing a pentachloroethane solution with a concentration of 15 mg/mL of compound I or compound II, and then spin-coating the prepared solution at a speed of 3000 rpm for 30 seconds to deposit on the perovskite layer; 6) placing in a vacuum evaporation chamber, and evaporating the metal electrode on the surface of the hole transport layer by a vacuum evaporation method to obtain a perovskite solar cell device. 5. the method for preparing large-area perovskite solar cell device by the bicarbazole class small molecule hole transport material according to claim 4, is characterized in that: in step 2), _TiO slurry and ethanol are 1:6 , m/m. 6. the method for preparing large-area perovskite solar cell device by bicarbazole class small molecule hole transport material according to claim 4, is characterized in that: in step 4), FAI concentration is 1M, and _PbI Concentration is 1.1 M, the MABr concentration is 0.2M, the _PbBr2 concentration is 0.22M, and the CsI concentration is 0.065M.