TWI878660B - Electroluminescence wire - Google Patents

Abstract

The present disclosure provides an electroluminescent wire, which includes a center conductive wire, a hole transport layer, an electron transport layer, and a transparent conductive layer. The hole transport layer wraps the center conductive wire and includes a hole transport material. The electron transport layer wraps and directly contacts the hole transport layer, in which the electron transport layer includes an electron transport material and an organic additive, and the organic additive generates hydrogen bonding force with the hole transport material and the electron transport material. The transparent conductive layer wraps the electron transport layer.

Description

Electroluminescence

The present disclosure relates to a light emitting device, and more particularly to an electroluminescent light emitting device.

In recent years, electroluminescent light sources have been widely used in various display lighting devices. In existing electroluminescent elements, high voltage is usually required to achieve high luminous brightness. However, there are concerns and risks in the safety of using high-voltage electroluminescent elements.

In order to improve the luminous brightness or light output, existing linear electroluminescent elements often configure additional functional layers on their central electrodes, such as a strong reflective layer, an inner electron emission layer or an outer electron emission layer. However, this method complicates the manufacturing process, resulting in increased costs and line diameter, thereby limiting the application range of linear electroluminescent elements. Therefore, there is an urgent need for a novel electroluminescent element to solve the above problems.

The present disclosure provides an electroluminescent light emitting device which can be driven by low voltage direct current to have high luminous brightness.

According to some embodiments of the present disclosure, an electroluminescent line includes a central conductor, a hole transport layer, an electron transport layer, and a transparent conductive layer. The hole transport layer surrounds the central conductor, and the hole transport layer includes a hole transport material. The electron transport layer surrounds and directly contacts the hole transport layer, wherein the electron transport layer includes an electron transport material and an organic additive, and the organic additive generates hydrogen bonding forces with the hole transport layer and the electron transport material. The transparent conductive layer surrounds the electron transport layer.

In some embodiments of the present disclosure, the content of the organic additive may be between 0.5 wt % and 10 wt % based on the total weight of the electron transport layer.

In some embodiments of the present disclosure, the weight average molecular weight of the organic additive may be between 100 g/mole and 2000 g/mole.

In some embodiments of the present disclosure, the organic additive may have an amino group, a hydroxyl group, a carboxyl group, or a combination thereof.

In some embodiments of the present disclosure, the highest occupied molecular orbital (HOMO) of the hole transport material may be between -5.1 eV and -5.9 eV.

In some embodiments of the present disclosure, the lowest unoccupied molecular orbital (LUMO) of the electron transport material may be between -4.2 eV and -2.5 eV.

In some embodiments of the present disclosure, the thickness of the hole transport layer may be between 30 nm and 90 nm, and the thickness of the electron transport layer may be between 30 nm and 90 nm.

In some embodiments of the present disclosure, the diameter of the electroluminescent line may be between 185 μm and 225 μm.

In some embodiments of the present disclosure, the hole transport layer, the electron transport layer and the transparent conductive layer can wrap around the central conductive line with uniform thickness.

In some embodiments of the present disclosure, the transparent conductive layer includes metal nanowires, and the content of the metal nanowires may be between 4 wt % and 6 wt % based on the total weight of the transparent conductive layer.

According to the above-mentioned embodiments of the present disclosure, the electroluminescent line can emit light efficiently at the interface between the hole transport layer and the electron transport layer by virtue of the hydrogen bonding force provided by the organic additive, thereby omitting the provision of the luminescent layer (e.g., fluorescent material and phosphorescent material). In this way, the electroluminescent line can be driven by low-voltage direct current, thereby reducing energy consumption and ensuring safety in use, and can achieve a thinning effect, thereby improving the convenience and aesthetics of being configured on wearable clothing.

The following will disclose multiple embodiments of the present disclosure with drawings. For the purpose of clarity, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present disclosure. In other words, in some embodiments of the present disclosure, these practical details are not necessary and therefore should not be used to limit the present disclosure. In addition, in order to simplify the drawings, some commonly used structures and components will be depicted in the drawings in a simple schematic manner. In addition, in order to facilitate the reader's viewing, the size of each component in the drawings is not drawn according to the actual scale.

The present disclosure provides an electroluminescent line having a hole transport layer and an electron transport layer in contact with each other, and the electron transport layer includes an organic additive. The electroluminescent line can emit light efficiently at the interface between the hole transport layer and the electron transport layer by virtue of the hydrogen bonding force provided by the organic additive, thereby omitting the provision of a luminescent layer (e.g., fluorescent and phosphorescent materials). In this way, the electroluminescent line can be driven by low-voltage direct current, thereby reducing energy consumption and ensuring safety in use, and can achieve a thinning effect, thereby improving the convenience and aesthetics of being configured on wearable clothing.

FIG. 1 is a three-dimensional exploded schematic diagram of an electroluminescent line 100 according to some embodiments of the present disclosure. FIG. 2 is a cross-sectional schematic diagram of the electroluminescent line 100 along the line segment AA' of FIG. 1. Please refer to FIG. 1 and FIG. 2 simultaneously. The electroluminescent line 100 includes a central conductor 110, a hole transport layer 120, an electron transport layer 130, and a transparent conductive layer 140. The hole transport layer 120 includes a hole transport material 122, and the electron transport layer 130 includes an electron transport material 132 and an organic additive 134. The transparent conductive layer 140 surrounds the electron transport layer 130, the electron transport layer 130 surrounds and directly contacts the hole transport layer 120, and the hole transport layer 120 surrounds the central conductive line 110. It should be particularly noted that the "enclosing a certain component" mentioned herein means "enclosing and surrounding the extended surface of the component", which will not be repeated below. In some embodiments, the transparent conductive layer 140 can directly contact the electron transport layer 130, and the hole transport layer 120 can directly contact the central conductive line 110.

The center conductor 110 is configured to serve as a center electrode of the electroluminescent line 100. In some embodiments, the material of the center conductor 110 may include a conductive metal, such as copper, gold, silver, nickel, cadmium, platinum, palladium, or any combination thereof. In other embodiments, the material of the center conductor 110 may include a conductive metal oxide, such as indium tin oxide. By selecting the above materials, the center conductor 110 may have a work function within a specific range, thereby improving the conductivity of the center conductor 110. In some embodiments, the work function of the center conductor 110 may be, for example, between -4.4 eV and -5.6 eV.

The hole transport layer 120 surrounds the central wire 110, and the electron transport layer 130 surrounds and directly contacts the hole transport layer 120. In some embodiments, the highest occupied molecular orbital of the hole transport material 122 of the hole transport layer 120 is between -5.1 eV and -5.9 eV, and the lowest unoccupied molecular orbital of the electron transport material 132 of the electron transport layer 130 is between -4.2 eV and -2.5 eV. The hole transport layer 120 and the electron transport layer 130 are configured to establish an energy level difference between holes and electrons, thereby adjusting the wavelength of light emitted by the electroluminescent line 100 according to actual needs. Specifically, through the mutual matching between the highest occupied molecular orbital of the hole transport material 122 and the lowest unoccupied molecular orbital of the electron transport material 132, the electroluminescent line 100 can emit light with a wavelength between 470nm and 600nm (i.e., the wavelength range of the light that can be emitted covers blue light to red light), thereby making the electroluminescent line 100 diverse and widely applicable.

In some embodiments, the hole transport material 122 of the hole transport layer 120 may include a p-type metal oxide, a p-type organic compound, a p-type organic metal compound, or any combination thereof. Specifically, the p-type metal oxide may be, for example, molybdenum trioxide (MoO3), tungsten trioxide (WO3), or any combination thereof; the p-type organic compound and the p-type organic metal compound may be, for example, NPB, TCTA, TAPC, mCP, CBP, CuPc, or any combination thereof. By selecting the above materials, the highest occupied molecular orbital of the hole transport layer 120 may fall within a suitable range. Note 1: NPB is N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine. Note 2: TCTA is 4,4',4"-tris(carbazol-9-yl)-triphenylamine. Note 3: TAPC is di-[4-(N,N-di-ρ-tolyl-amino)-phenyl]cyclohexane. Note 4: mCP is 1,3-di-9-carbazolylbenzene. Note 5: CBP is 4,4'-N,N'-dicarbazole-biphenyl. Note 6: CuPc is copper phthalocyanine.

In some embodiments, the electron transport material 132 of the electron transport layer 130 may include an n-type organic compound. Specifically, the n-type organic compound may be, for example, Alq ₃ , TPBi, B3PYMPM, TmPyPB, PO-T2T, or any combination thereof. By selecting the above materials, the lowest unoccupied molecular orbital of the electron transport layer 130 can fall within a suitable range. Note 7: Alq ₃ is tris(8-hydroxyquinoline) aluminum. Note 8: TPBi is 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene. Note 9: B3PYMPM is 4,6-bis(3,5-di(pyridin-3-yl)phenyl)-2-methylpyrimidine. Note 10: TmPyPB is 3,3'-[5'-[3-(3-Pyridinyl)phenyl][1,1':3',1"-terphenyl]-3,3"-diyl]bispyridine. Note 11: PO-T2T is 2,4,6-Tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine.

The electron transport layer 130 includes an organic additive 134, and the organic additive 134 is configured to generate hydrogen bonding forces with the hole transport material 122 and the electron transport material 132, thereby shortening the distance between the hole transport material 122 and the electron transport material 132 at the interface between the hole transport layer 120 and the electron transport layer 130. In this way, holes and electrons can have good bonding ability at the interface between the hole transport layer 120 and the electron transport layer 130, so that the electroluminescent line 100 has high light emission efficiency, so that the electroluminescent line 100 can have high light emission brightness through low voltage direct current driving. In some embodiments, the organic additive 134 may have a functional group of an amine group, an NH group, a hydroxyl group, a carboxyl group, or a combination thereof to generate a strong hydrogen bonding force, thereby making the electroluminescent line 100 have a high light emission efficiency. Specifically, the organic additive 134 may be, for example, polyethylene glycol (PEG), polysorbate 20 (Tween 20), trifluoroethanol, Triton X-100 (C ₁₄ H ₂₂ O(C ₂ H ₄ O) _n , where n may be 9 or 10), aminobenzamidine hydrochloride, gallic acid, or a combination thereof.

In some embodiments, the content of the organic additive 134 may be between 0.5 wt % and 10.0 wt % based on the total weight of the electron transport layer 130, and the weight average molecular weight of the organic additive 134 may be between 100 g/mole and 2000 g/mole to provide strong hydrogen bonding forces and ensure good electrical conductivity between the layers. Specifically, when the content of the organic additive 134 is less than 0.5 wt% and/or the weight average molecular weight of the organic additive 134 is less than 100 g/mole, it is easy to cause the strength of the hydrogen bond force to be insufficient; when the content of the organic additive 134 is greater than 10.0 wt% and/or the weight average molecular weight of the organic additive 134 is greater than 2000 g/mole, it is easy to reduce the conductivity between the layers, which is not conducive to the combination of holes and electrons to further emit light. It should be particularly noted that, since the organic additive 134 disclosed herein is located between the electron transport materials 132 and not between the hole transport materials 122, it is possible to prevent the electrons in the organic additive 134 used to form hydrogen bonds from combining with the holes in the hole transport materials 122, thereby allowing the organic additive 134 to perform its function well.

The transparent conductive layer 140 surrounds the electron transport layer 130. In some embodiments, the transparent conductive layer 140 may include a plurality of metal nanowires such as silver nanowires, wherein the diameter of each silver nanowire may be between 50 nm and 100 nm, and the length of each silver nanowire may be between 5 μm and 50 μm. In some embodiments, silver nanowires having a content of about 5 wt% may be uniformly mixed in ethanol (i.e., the content of silver nanowires is about 5 wt% based on the total weight of the two) to form a silver nanowire suspension, and the silver nanowire suspension is disposed to surround the electron transport layer 130 by wet coating, thereby forming the transparent conductive layer 140. In some embodiments, based on the total weight of the transparent conductive layer 140 , the content of the metal nanowires may be between 4 wt % and 6 wt %, thereby taking both the conductivity and light transmittance of the transparent conductive layer 140 into consideration.

In some embodiments, the electroluminescent line 100 may further include a transparent protective layer 150. The transparent protective layer 150 is configured to uniformly surround and protect the transparent conductive layer 140, thereby preventing the transparent conductive layer 140 and the electroluminescent line 100 from being damaged during use. In some embodiments, the material of the transparent protective layer 150 may include ethylene vinyl acetate (EVA), polyvinyl acetate (PVAC), or any combination thereof.

In some embodiments, the electroluminescent line 100 may have a specific thickness and flexibility, making it suitable for use in various types of electroluminescent elements. In some embodiments, excluding the transparent protective layer 150, the diameter D1 of the electroluminescent line 100 (i.e., the line diameter D1) may be between 185 μm and 225 μm, and the bending radius of the electroluminescent line 100 may be between 3.0 mm and 5.0 mm, so that the electroluminescent line 100 can be applied to products such as wires, fabrics, or advertising box backlights. The diameter D1 of the electroluminescent line 100 can be controlled, for example, by the diameter or thickness of each layer therein. In some embodiments, the diameter D2 of the central conductive line 110 may be between 160 μm and 175 μm, so that it has good flexibility. In some embodiments, the thickness H2 of the hole transport layer 120 may be between 30 nm and 90 nm, preferably 70 nm, and the thickness H3 of the electron transport layer 130 may be between 30 nm and 59 nm, preferably 50 nm. Since the hole transport layer 120 and the electron transport layer 130 each have a sufficiently small thickness, it can help electrons and holes to combine at the interface between the hole transport layer 120 and the electron transport layer 130, so that the electroluminescent line 100 can be driven by low voltage direct current and the overall luminous brightness of the electroluminescent line 100 is improved. In some embodiments, the thickness H4 of the transparent conductive layer 140 may be between 25 μm and 45 μm to provide good electron transmittance, thereby improving the overall luminous efficiency of the electroluminescent line 100, and when the transparent conductive layer 140 includes metal nanowires, this thickness range can take into account both the conductivity and light transmittance of the transparent conductive layer 140. In some embodiments, the thickness H6 of the transparent protective layer 150 may be between 1000 μm and 3000 μm to provide good protection. It should be noted that in order to make the diagram clearly represent the relationship between the various stacked layers and the various components in the electroluminescent line 100, Figures 1 and 2 do not depict the above-mentioned various stacked layers and various components according to the actual scale, and the content of the present disclosure should not be limited to the proportional relationship represented by Figures 1 and 2.

In some embodiments, the manufacturing method of the electroluminescent line 100 may include sequentially forming a hole transport layer 120 including a hole transport material 122, an electron transport layer 130 including an electron transport material 132 and an organic additive 134, a transparent conductive layer 140, and a transparent protective layer 150 by wet or dry coating, and configuring the above layers in a wire-drawing manner to wrap around the central conductor 110. The layers formed by the above method can wrap around the central conductor 110 with a suitable and uniform thickness, thereby improving the luminous uniformity of the electroluminescent line 100 and increasing the application range of the electroluminescent line 100. It should be understood that the “uniform thickness” mentioned here may refer to “the total thickness of each layer is uniform”, and preferably refers to “the thickness of each layer is uniform”. In some embodiments, the hole transport material 122 (e.g., TAPC) may be dissolved in toluene and stirred with a magnet for about 10 minutes to prepare a slurry for forming the hole transport layer 120. In some embodiments, the organic additive 134 and the electron transport material 132 (e.g., TmPyTZ) may be dissolved in butanol and stirred with a magnet for about 10 minutes to prepare a slurry for forming the electron transport layer 130.

In the following description, the brightness of the electroluminescent wires of each comparative example and each embodiment will be tested. The manufacturing method of the electroluminescent wire of each embodiment refers to the manufacturing method of the electroluminescent wire mentioned above, and will not be repeated here. Unless otherwise noted, in the electroluminescent wire of each embodiment, the central wire has a wire diameter of 168μm, and its material is indium tin oxide; the hole transport layer has a thickness of 70 nm; the electron transport layer has a thickness of 50 nm; the transparent conductive layer has a thickness of 34μm, and its material includes the aforementioned silver nanowire; the material of the transparent protective layer is polyurethane resin. In addition, the brightness of the electroluminescent line of each experimental example was tested using a direct current of 20 volts, and the brightness was measured using a colorimeter (purchased from TOPCON, product model BM7). <Experimental Example 1: Test on the influence of organic additives of different materials on the brightness of electroluminescent line>

In this experimental example, the electroluminescent line of each embodiment includes organic additives of different materials, wherein the hole transport material of the hole transport layer is TCTA, the electron transport material of the electron transport layer is PO-T2T, and when calculated based on the total weight of the electron transport layer, the content of the organic additive is 2wt%. The materials of the organic additives in the electroluminescent line of each embodiment and the brightness test results of the electroluminescent line are shown in Table 1.

Table 1 Materials of organic additives Luminance(cd/m ² ) Comparison Example 1 No Additive 621 Comparison Example 2 No Additives (See Note 12 for details) 853 Comparison Example 3 No Additives (See Note 13 for details) 148 Embodiment 1 PEG (molecular weight 400 g/mole) 1768 Embodiment 2 Tween 20 1467 Embodiment 3 Triton X-100 1300 Embodiment 4 gallic acid 1892 Embodiment 5 aminobenzamidine 1721 Embodiment 6 trifluoroethanol 1822 Note 12: The hole transport material of Comparative Example 2 is NPB, the thickness of the hole transport layer is 50nm, the electron transport material is PO-T2T, the thickness of the electron transport layer is 40nm, and a luminescent layer is arranged between the hole transport layer and the electron transport layer. The material of the luminescent layer is CBP: 5% Irppy ₂ acac, and the thickness of the luminescent layer is 30nm. In addition, the brightness of the electroluminescent line of Comparative Example 2 is tested using a direct current of 25 volts. Note 13: The hole transport layer material of Comparative Example 3 is NPB, the thickness of the hole transport layer is 46nm, the electron transport material is 8-Hydroxyquinolinolato-lithium (Liq), the thickness of the electron transport layer is 53nm, a luminescent layer is arranged between the hole transport layer and the electron transport layer, the material of the luminescent layer is ZnS, and the thickness of the luminescent layer is 33μm, a dielectric layer is arranged between the hole transport layer and the central conductor, the material of the dielectric layer is BaTiO ₃ , and the thickness of the dielectric layer is 22μm. In addition, the brightness of the electroluminescent line of Comparative Example 3 is tested using an alternating current with a voltage of 160V and a frequency of 11.6KHz.

The experimental results show that the luminance of the electroluminescent line of each embodiment is much greater than that of the electroluminescent line of each comparative example, and is about three times that of the electroluminescent line of each comparative example, indicating that the configuration of the hole transport material of the hole transport layer and the electron transport material of the electron transport layer and the organic additive can effectively improve the overall luminance of the electroluminescent line. In addition, when gallic acid is used as the material of the organic additive, the overall luminance of the electroluminescent line can be increased to nearly 1900 cd/ ^m2 , with better optical performance. On the other hand, compared with each comparative example, the electroluminescent line of each embodiment can be driven by a low voltage (20V) DC power, thereby reducing energy consumption. ＜Experimental Example 2: Test on the effect of different contents of organic additives on the brightness of electroluminescent light＞

In this experimental example, different contents of organic additives were added to the electron transport layer, wherein the hole transport material of the hole transport layer was TCTA; the electron transport material was PO-T2T, and the material of the organic additive was PEG (molecular weight of 300 g/mole). The contents of the organic additives in the electroluminescent line of each embodiment (based on the total weight of the electron transport layer) and the brightness test results of the electroluminescent line are shown in Table 2.

Table 2 Content of organic additives Luminance(cd/m ² ) Embodiment 7 1wt% 1454 Embodiment 8 2wt% 1602

The experimental results show that the electroluminescent line of each embodiment has a luminance greater than 1400 cd/ ^m2 . It can be seen that the appropriate adjustment of the content of the organic additive can provide a strong hydrogen bonding force and ensure that the layers can maintain good conductivity, thereby effectively improving the overall luminous brightness of the electroluminescent line. <Experimental Example 3: Test of the influence of organic additives of different molecular weights on the luminous brightness of the electroluminescent line>

In this experimental example, organic additives of different molecular weights were added to the electron transport layer, wherein the hole transport material of Examples 9 to 11 and 13 was TCTA, the hole transport material of Example 12 was NPB, the electron transport material of Examples 9 to 12 was PO-T2T, the material of the organic additive was PEG, and when calculated based on the total weight of the electron transport layer, the content of the organic additive was 2 wt%. The molecular weight of the organic additive in the electroluminescent line of each example and the brightness test results of the electroluminescent line are shown in Table 3.

Table 3 Molecular weight of organic additives Luminance(cd/m ² ) Embodiment 9 200 g/mole 1622 Embodiment 10 400 g/mole 1768 Embodiment 11 600 g/mole 1602 Embodiment 12 600 g/mole 1532 Embodiment 13 1000 g/mole 1354

The experimental results show that the electroluminescent lines of each embodiment have a luminance greater than 1300 cd/ ^m2 . It can be seen that properly adjusting the molecular weight of the organic additive can provide strong hydrogen bonding forces and ensure that the layers can maintain good conductivity, thereby effectively improving the overall luminous brightness of the electroluminescent line. <Experimental Example 4: Test on the influence of different materials of the central conductor on the luminous brightness of the electroluminescent line>

In this experimental example, the electroluminescent line of each embodiment has a central conductive line of different materials, wherein the hole transport material is TCTA, the electron transport material is PO-T2T, the material of the organic additive is gallic acid, and when calculated based on the total weight of the electron transport layer, the content of the organic additive is 2wt%. The material of the central conductive line in the electroluminescent line of each embodiment and the brightness test results of the electroluminescent line are shown in Table 4.

Table 4 Center conductor material Luminance(cd/m ² ) Embodiment 14 Gold (work function: 5.10 eV) 1835 Embodiment 15 Silver (work function: 4.26eV) 1523 Embodiment 16 Copper (work function: 4.65eV) 1348 Embodiment 17 Cadmium (work function: 5.22eV) 1963 Embodiment 18 Platinum (work function: 5.65eV) 1786 Embodiment 19 Indium Tin Oxide (Work Function: 4.70eV) 1892

The experimental results show that the electroluminescent line of each embodiment has a luminance greater than 1300 cd/m ² , indicating that the overall luminance of the electroluminescent line can be effectively improved by the special configuration of the hole transport material of the hole transport layer and the electron transport material of the electron transport layer and the organic additives and the selection of a center conductor of suitable material. In addition, when cadmium is used as the material of the center conductor, the overall luminance of the electroluminescent line can be increased to nearly 2000 cd/m ² , with better optical performance.

According to the above-mentioned implementation method of the present disclosure, the electroluminescent wire of the present disclosure has a hole transport layer and an electron transport layer that are in contact with each other and an organic additive doped in the electron transport layer. Through the hydrogen bonding force provided by the organic additive, the electroluminescent wire can emit light efficiently at the interface between the hole transport layer and the electron transport layer, thereby omitting the provision of a luminescent layer (for example, a fluorescent material and a phosphorescent material). In this way, the electroluminescent wire can be driven by low-voltage direct current, thereby reducing energy consumption and ensuring safety in use, and can achieve a thinning effect, thereby improving the convenience and aesthetics of being configured on wearable clothing.

Although the present disclosure has been disclosed in the above implementation form, it is not intended to limit the present disclosure. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the definition of the attached patent application scope.

110: Central conductor 120: Hole transport layer 122: Hole transport material 130: Electron transport layer 132: Electron transport material 134: Organic additive 140: Transparent conductive layer 150: Transparent protective layer H2~H4,H6: Thickness D1~D2: Diameter A-A': Line segment

In order to make the above and other purposes, features, advantages and embodiments of the present disclosure more clearly understandable, the attached drawings are described as follows: FIG. 1 is a three-dimensional exploded schematic diagram of an electroluminescent line according to some embodiments of the present disclosure; and FIG. 2 is a cross-sectional schematic diagram of the electroluminescent line along the line segment A-A' of FIG. 1 .

Domestic storage information (please note in the order of storage institution, date, and number) None Foreign storage information (please note in the order of storage country, institution, date, and number) None

110: Center wire

120: hole transport layer

122: Hole transport materials

130:Electron transmission layer

132:Electronic transmission materials

134: Organic additives

140: Transparent conductive layer

150: Transparent protective layer

H2~H4,H6:Thickness

D1~D2: Diameter

Claims (9)

An electroluminescent line includes: a central conductor; a hole transport layer surrounding the central conductor, wherein the hole transport layer includes a hole transport material; an electron transport layer surrounding and directly contacting the hole transport layer, wherein the electron transport layer includes an electron transport material and an organic additive, and the organic additive generates hydrogen bonding forces with the hole transport material and the electron transport material; and a transparent conductive layer surrounding the electron transport layer, wherein the hole transport layer, the electron transport layer and the transparent conductive layer surround the central conductor with uniform thickness. The electroluminescent line as described in claim 1, wherein the content of the organic additive is between 0.5wt% and 10wt% based on the total weight of the electron transport layer. The electroluminescent line as described in claim 1, wherein the weight average molecular weight of the organic additive is between 100 g/mole and 2000 g/mole. The electroluminescent line as described in claim 1, wherein the organic additive has a functional group of an amine group, a hydroxyl group, a carboxyl group or a combination thereof. An electroluminescent line as described in claim 1, wherein the highest occupied molecular orbital of the hole transport material is between -5.1eV and -5.9eV. An electroluminescent line as described in claim 1, wherein the lowest unoccupied molecular orbital of the electron transport material is between -4.2eV and -2.5eV. The electroluminescent line as described in claim 1, wherein the thickness of the hole transport layer is between 30nm and 90nm, and the thickness of the electron transport layer is between 30nm and 90nm. The electroluminescent line as described in claim 1, wherein the diameter of the electroluminescent line is between 185μm and 225μm. The electroluminescent line as described in claim 1, wherein the transparent conductive layer comprises metal nanowires, and the content of the metal nanowires is between 4 wt % and 6 wt % based on the total weight of the transparent conductive layer.

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