Thieno[3,2-b]indole-based hole transport material and synthesis method thereof

Abstract

The application discloses a kind of hole transport material based on thieno [3, 2-b] indole and synthesis method thereof.The center core molecule thieno [3, 2-b] indole core is applied as module in perovskite solar cell hole transport material, different carbon bran, methoxyaniline and 4-methoxy-N-(4-methoxyphenyl)-N-phenylaniline are introduced, the introduction of different groups can effectively improve the energy level and hole mobility of molecule, so that the material can have better hole transport capacity, improve device performance, improve photoelectric conversion efficiency, improve device stability.

Description

Technical Field

[0001] This invention belongs to the field of perovskite solar cells and relates to a hole transport material based on thiopheno[3,2-b]indole and its synthesis method. Background Technology

[0002] Organic perovskite solar cells (PSCs) possess unique optical and electrical properties, making them a key research focus in next-generation photovoltaics. In just a few years, the power conversion efficiency (PCE) of PSCs has significantly improved from 3.8% to over 25.7%. Despite this improvement in PCE, the commercialization of such PSCs has been hampered by their limited device stability.

[0003] Typically, the best-performing conventional PSCs consist of an electron-selective layer, an n-type mesoporous metal oxide scaffold, a perovskite layer, a p-type hole transport material (HTM), and a metal electrode. The performance of small-molecule HTMs is closely related to the structure of the central core, which significantly affects the hole carrier mobility of the HTM layer. Notably, strong intermolecular p–p stacking has been shown to be key to improving hole carrier mobility. Studies have shown that electron-rich fused heterocycles, such as carbazole, not only favor p–p stacking but also hole extraction.

[0004] Thieno[3,2-b]indole, with its central core, possesses a p-p stacked structure, and its strong electron-donating ability and coplanarity are beneficial for hole extraction in perovskite solar cells. Currently, thieno[3,2-b]indole is mainly used in dye-sensitized solar cells (DSSC) and as a sensitizer in mesoporous titanium dioxide thin films. It is also used as a structural side chain in solar cells. However, its thermal stability is low, and its material decomposition temperature is only 300-350℃ (Zhou X, Lu J, Huang H, et al. Thieno[3,2-b]indole (TI) bridged A-π-D-π-A small molecules: Synthesis, characterizations and organic solar cell applications[J]. Dyes and Pigments, 2018, 160.). Therefore, the development and design of hole transport layer materials based on thieno[3,2-b]indole with high hole mobility, low cost, and strong stability are of great significance for promoting the basic research and commercial application of perovskite solar cells. Summary of the Invention

[0005] The purpose of this invention is to provide a hole transport material based on thiopheno[3,2-b]indole and its synthesis method. This hole transport material has high thermal stability and can be used in perovskite solar cells.

[0006] The technical solution for achieving the objective of this invention is as follows:

[0007] Hole transport materials based on thiopheno[3,2-b]indole have the following structural formula:

[0008]

[0009]

[0010]

[0011]

[0012] A method for synthesizing hole transport materials based on thieno[3,2-b]indole includes the following steps:

[0013] (1) Under nitrogen protection, 1,4-dibromo-2-nitrobenzene and 2-tributyltinylthiophene undergo a Still coupling reaction at 100–110 °C catalyzed by tetrakis(triphenylphosphine)palladium (Pd(PPh3)4) to generate 2-(4-bromo-2-nitrobenzene)thiophene.

[0014]

[0015] (2) Using chlorobenzene as a solvent, 2-(4-bromo-2-nitrophenyl)thiophene reacts at 135–145 °C under the catalysis of triphenylphosphine (PPh3) to generate 6-bromo-4H-thiopheno[3,2-b]indole.

[0016]

[0017] (3) Using N,N-dimethylformamide (DMF) as solvent, 6-bromo-4H-thieno[3,2-b]indole reacts with bromoisooctane at 35–45 °C under the action of sodium hydride to generate 6-bromo-4-(2-ethylhexyl)-4H-thieno[3,2-b]indole.

[0018]

[0019] Alternatively, using DMF as a solvent, 6-bromo-4H-thieno[3,2-b]indole reacts with dodecyl bromide in the presence of sodium hydride at 35–45 °C to generate 6-bromo-4-dodecyl-4H-thieno[3,2-b]indole.

[0020]

[0021] Alternatively, in an aqueous solution of dimethyl ethylene glycol (DME) and potassium hydroxide, 6-bromo-4H-thieno[3,2-b]indole reacts with p-iodoanisole, cuprous iodide, and 1,10-phenanthroline at 90–95 °C to generate 6-bromo-4-(4-methoxyphenyl)-4H-thieno[3,2-b]indole.

[0022]

[0023] Alternatively, in an aqueous solution of DME and potassium hydroxide, 6-bromo-4H-thieno[3,2-b]indole, 4-iodo-N,N-bis(4-methoxyphenyl)aniline, cuprous iodide, and 1,10-phenanthroline react at 90–95 °C to generate 4-(6-bromo-4H-thieno[3,2-b]indole-4-yl)-N,N-bis(4-methoxyphenyl)aniline.

[0024]

[0025] (4) Using tetrahydrofuran as a solvent, the product from step (3) and N-bromosuccinimide react at 0°C to generate an intermediate.

[0026]

[0027]

[0028] (5) In the presence of tetrahydrofuran and sodium carbonate aqueous solution, the intermediate and 4-boron ester-4',4'-dimethoxytriphenylamine react at 75–80 °C under the catalysis of tetratriphenylphosphine palladium to generate the target product.

[0029]

[0030] Furthermore, in step (1), the molar ratio of 4-dibromo-2-nitrobenzene to 2-tributyltinylthiophene is 1:0.9.

[0031] Furthermore, in step (2), the molar ratio of 2-(4-bromo-2-nitrophenyl)thiophene to triphenylphosphine is 1:5.

[0032] Furthermore, in step (3), the volume ratio of ethylene glycol dimethyl ether to water is 1:2.

[0033] Furthermore, in step (5), the volume ratio of tetrahydrofuran to water is 1:1.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] (1) The synthesis method of this invention is simple. The synthesized compound based on thieno[3,2-b]indole core and 4-methoxy-N-(4-methoxyphenyl)-N-phenylaniline as end groups has a high glass transition temperature (90-100℃), high thermal stability, high thermal decomposition temperature (400-450℃), and high HOMO energy level (-5.11-5.00eV). When used as a calcium hole transport material in perovskite solar cells, it can improve the hole transport mobility in solar cells and thus improve the stability of the device.

[0036] (2) In this invention, the central core molecule thiopheno[3,2-b]indole is used as a module in the hole transport material of perovskite solar cells. Different carbon branches, methoxyaniline and 4-methoxy-N-(4-methoxyphenyl)-N-phenylaniline are introduced. The introduction of different groups can effectively improve the energy level and hole mobility of the molecule, so that the material can have better hole transport capability, improve device performance, improve photoelectric conversion efficiency and improve device stability. Attached Figure Description

[0037] Figure 1 Cyclic voltammetry curves for BPTPA-C12(a), BPTPA-C2C6(b), BPTPA-PhOMe(c), and BPT-3TPA(d).

[0038] Figure 2 The UV-Vis absorption spectra of BPTPA-C12, BPTPA-C2C6, BPTPA-PhOMe, and BPT-3TPA material solutions (a) and after coating (b).

[0039] Figure 3 Thermogravimetric analysis curves for BPTPA-C12, BPTPA-C2C6, BPTPA-PhOMe, and BPT-3TPA materials.

[0040] Figure 4 Differential scanning calorimetry curves for BPTPA-C12, BPTPA-C2C6, BPTPA-PhOMe, and BPT-3TPA materials. Detailed Implementation

[0041] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0042] The following examples demonstrate how the optical properties of materials are determined by measuring the structure of the final product through nuclear magnetic resonance spectroscopy, the electrochemical properties of materials are characterized by cyclic voltammetry, and the stability of materials is characterized by thermogravimetric analysis and differential scanning calorimetry.

[0043] Example 1: Synthesis of 4,4'-(4-dodecyl-4H-thieno[3,2-b]indole-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (BPTPA-C12):

[0044] (1) Under nitrogen protection, 1,4-dibromo-2-nitrobenzene and 2-tributylmethyltinylthiophene undergo a Still coupling reaction at 110 °C catalyzed by Pd(PPh3)4 to produce 2-(4-bromo-2-nitrobenzene)thiophene.

[0045]

[0046] (2) Using chlorobenzene as a solvent, 2-(4-bromo-2-nitrophenyl)thiophene reacts at 140℃ under the catalysis of PPh3 to generate 6-bromo-4H-thiopheno[3,2-b]indole (BPT-BR).

[0047]

[0048] (3) Synthesis of compound 6-bromo-4-dodecyl-4H-thiophene[3,2-b]indole (BPT-C12-BR):

[0049]

[0050] NaH (2.86 g, 71 mmol) was slowly added to a solution of BPT-BR (1.8 g, 7.14 mmol) dissolved in anhydrous DMF (30 mL), and the reaction mixture was stirred at 40 °C under argon for 40 min. Bromoisooctane (1.78 g, 7.14 mmol) was added to the solution, and the reaction mixture was stirred at 40 °C under nitrogen atmosphere for 4 h. The resulting mixture was quenched with distilled water (3 mL) and then extracted with dichloromethane (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-C12-BR was obtained by vacuum distillation and purified by silica gel column chromatography in 82% yield.

[0051] (4) Synthesis of compound 2,6-dibromo-4-dodecyl-4H-thiophene[3,2-b]indole (BPT-C12-2BR):

[0052]

[0053] NBS (1.69 g, 9.51 mmol) was slowly added in portions to a solution of BPT-C12-BR (2 g, 4.76 mmol) in tetrahydrofuran solvent at 0 °C. The mixture was stirred overnight at room temperature. The reaction mixture was quenched with water (30 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-C12-2BRr was purified by vacuum distillation and silica gel column chromatography in 89% yield.

[0054] (5) Synthesis of compound 4,4'-(4-dodecyl-4H-thieno[3,2-b]indole-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (BPTPA-C12):

[0055]

[0056] In a round-bottom flask, BPT-C12-2BR (0.8 g, 1.6 mmol), OMETPA-BPIN (3.46 g, 8.01 mmol), Pd(PPh3)4 (0.2 g, 0.17 mmol), and tetrahydrofuran solvent (35 mL) were added, followed by an aqueous sodium carbonate solution (4.43 g, 2 M). The reaction was refluxed under nitrogen for 12 hours. The resulting mixture was quenched with distilled water (3 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPTPA-C12 was purified by vacuum distillation and silica gel column chromatography in 78% yield. 1 H NMR(500MHz,Methylene Chloride-d2)δ7.61–6.80(m,30H),4.28(t,J=7.2Hz,2H),3.80(s,12H),1.89(t,J=7.3Hz,2H),1.39–1.31(m,4H),1.22(s,15H),0.85(s,2H).

[0057] Example 2: Synthesis of 4,4'-(4-(2-ethylhexyl)-4H-thieno[3,2-b]indole-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (BPTPA-C2C6):

[0058] (1) Under nitrogen protection, 1,4-dibromo-2-nitrobenzene and 2-tributylmethyltinylthiophene undergo a Still coupling reaction at 110 °C catalyzed by Pd(PPh3)4 to produce 2-(4-bromo-2-nitrobenzene)thiophene.

[0059]

[0060] (2) Using chlorobenzene as a solvent, 2-(4-bromo-2-nitrophenyl)thiophene reacts at 140℃ under the catalysis of PPh3 to generate 6-bromo-4H-thiopheno[3,2-b]indole (BPT-BR).

[0061]

[0062] (3) Synthesis of compound 6-bromo-4-(2-ethylhexyl)-4H-thieno[3,2-b]indole (BPT-C2C6-BR):

[0063]

[0064] NaH (2.7 g, 67 mmol) was slowly added to a solution of BPT-BR (1.7 g, 6.7 mmol) dissolved in anhydrous DMF (30 mL), and the reaction mixture was stirred at 40 °C under argon for 40 min. Bromoisooctane (1.3 g, 6.7 mmol) was added to the solution, and the reaction mixture was stirred at 40 °C under nitrogen atmosphere for 4 h. The resulting mixture was quenched with distilled water (3 mL) and then extracted with dichloromethane (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-C2C6-BR was obtained by vacuum distillation and purified by silica gel column chromatography in 82% yield.

[0065] (4) Synthesis of compound 2,6-dibromo-4-(2-ethylhexyl)-4H-thieno[3,2-b]indole (BPT-C2C6-2BR):

[0066]

[0067] NBS (0.88 g, 4.94 mmol) was slowly added in portions to a solution of BPT-C2C6-BR (0.9 g, 2.47 mmol) in tetrahydrofuran solvent at 0 °C. The mixture was stirred overnight at room temperature. The reaction mixture was quenched with water (30 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-C2C6-2BRr was purified by vacuum distillation and silica gel column chromatography in 90% yield.

[0068] (5) Synthesis of compound 4,4'-(4-(2-ethylhexyl)-4H-thieno[3,2-b]indole-2,6-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) (BPTPA-C2C6):

[0069]

[0070] In a round-bottom flask, BPT-C2C6-2BR (0.36 g, 0.8 mmol), OMETPA-BPIN (1.75 g, 4.06 mmol), Pd(PPh3)4 (0.2 g, 0.17 mmol), and tetrahydrofuran solvent (35 mL) were added, followed by an aqueous sodium carbonate solution (0.72 g, 2 M). The reaction was refluxed under nitrogen for 12 hours. The resulting mixture was quenched with distilled water (3 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPTPA-C2C6 was purified by vacuum distillation and silica gel column chromatography in 79% yield. 1 H NMR (500MHz, CD2Cl2, δ): 7.64–6.60 (m, 28H), 4.16 (t, J = 7.7Hz, 2H), 3.80 (s, 12H), 2.10–2.04 ( m,1H),1.43–1.33(m,4H),1.27(d,J=4.5Hz,4H),0.92(t,J=7.4Hz,3H),0.85(t,J=7.1Hz,3H).

[0071] Example 3: Synthesis of 4,4'-(4-(4-methoxyphenyl)-4H-thieno[3,2-b]indole-2,6-diyl)bis(N,N-bis(4-methylphenyl)aniline) (BPTPA-PhOMe):

[0072] (1) Under nitrogen protection, 1,4-dibromo-2-nitrobenzene and 2-tributylmethyltinylthiophene undergo a Still coupling reaction at 110 °C catalyzed by Pd(PPh3)4 to produce 2-(4-bromo-2-nitrobenzene)thiophene.

[0073]

[0074] (2) Using chlorobenzene as a solvent, 2-(4-bromo-2-nitrophenyl)thiophene reacts at 140℃ under the catalysis of PPh3 to generate 6-bromo-4H-thiopheno[3,2-b]indole (BPT-BR).

[0075]

[0076] (3) Synthesis of compound 6-bromo-4-(4-methoxyphenyl)-4H-thieno[3,2-b]indole (BPTPA-PhOMe-BR):

[0077]

[0078] In a round-bottom flask, BPT-BR (2.14 g, 8.49 mmol), p-iodoanisole (19.86 g, 84.88 mmol), CuI (1.3 g, 6.79 mmol), 1,10-phenanthroline (3.06 g, 16.98 mmol), and ethylene glycol dimethyl ether solvent (35 mL) were added, followed by an aqueous solution of potassium hydroxide (4.76 g, 85 mmol). The reaction was refluxed under nitrogen for 24 hours. The resulting mixture was quenched with distilled water (3 mL) and then extracted with dichloromethane (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPTPA-PhOMe-BR was obtained by vacuum distillation and purified by silica gel column chromatography in 83% yield.

[0079] (4) Synthesis of 2,6-dibromo-4-(4-methoxyphenyl)-4H-thieno[3,2-b]indole (BPTPA-PhOMe-2BR):

[0080]

[0081] NBS (0.79 g, 4.47 mmol) was slowly added in portions to a solution of BPT-PhOMe-BR (0.8 g, 2.23 mmol) in tetrahydrofuran solvent at 0 °C. The mixture was stirred overnight at room temperature. The reaction mixture was quenched with water (30 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-PhOMe-2BRr was purified by vacuum distillation and silica gel column chromatography in 89% yield.

[0082] (5) Synthesis of compound 4,4'-(4-(4-methoxyphenyl)-4H-thieno[3,2-b]indole-2,6-diyl)bis(N,N-bis(4-methylphenyl)aniline) (BPTPA-PhOMe):

[0083]

[0084] In a round-bottom flask, BPT-PhOMe-2BR (0.78 g, 1.78 mmol), OMETPA-BPIN (3.85 g, 8.92 mmol), Pd(PPh3)4 (0.04 g, 0.035 mmol), and tetrahydrofuran solvent (35 mL) were added, followed by an aqueous sodium carbonate solution (3.78 g, 2 M). The reaction was refluxed under nitrogen for 12 hours. The resulting mixture was quenched with distilled water (3 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPTPA-PhOMe was obtained by vacuum distillation and purified by silica gel column chromatography in 80% yield. 1H NMR (500MHz, CD2Cl2, δ): 7.57–6.83 (m, 32H), 3.89 (s, 6H), 3.79 (s, 6H), 1.28 (d, J = 15.5Hz, 3H).

[0085] Example 4: Synthesis of 4,4',4'-(4H-thieno[3,2-b]indole-2,4,6-triyl)tris(N,N-bis(4-methoxyphenyl)aniline) (BPT-3TPA):

[0086] (1) Under nitrogen protection, 1,4-dibromo-2-nitrobenzene and 2-tributylmethyltinylthiophene undergo a Still coupling reaction at 110 °C catalyzed by Pd(PPh3)4 to produce 2-(4-bromo-2-nitrobenzene)thiophene.

[0087]

[0088] (2) Using chlorobenzene as a solvent, 2-(4-bromo-2-nitrophenyl)thiophene reacts at 140℃ under the catalysis of PPh3 to generate 6-bromo-4H-thiopheno[3,2-b]indole (BPT-BR).

[0089]

[0090] (3) Synthesis of compound 4-(6-bromo-4H-thieno[3,2-b]indol-4-yl)-N,N-bis(4-methoxyphenyl)aniline (BPT-TPA-BR):

[0091]

[0092] In a round-bottom flask, BPT-BR (0.36 g, 1.43 mmol), 4-iodo-N,N-bis(4-methoxyphenyl)aniline (3.69 g, 8.57 mmol), CuI (0.7 g, 0.1 mmol), 1,10-phenanthroline (0.18 g, 0.1 mmol), and ethylene glycol dimethyl ether solvent (35 mL) were added, followed by an aqueous solution of potassium hydroxide (0.8 g, 14 mmol). The reaction was refluxed under nitrogen for 24 hours. The resulting mixture was quenched with distilled water (3 mL) and then extracted with dichloromethane (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-TPA-BR was obtained by vacuum distillation and purified by silica gel column chromatography in 82% yield.

[0093] (4) Synthesis of 4-(2,6-dibromo-4H-thieno[3,2-b]indol-4-yl)-N,N-bis(4-methoxyphenyl)aniline (BPT-TPA-2BR):

[0094]

[0095] NBS (0.18 g, 1.01 mmol) was slowly added in portions to a solution of BPT-TPA-BR (0.56 g, 1.01 mmol) in tetrahydrofuran solvent at 0 °C. The mixture was stirred overnight at room temperature. The reaction mixture was quenched with water (30 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-TPA-2BRr was purified by vacuum distillation and silica gel column chromatography in 89% yield.

[0096] (5) Synthesis of 4,4',4'-(4H-thieno[3,2-b]indole-2,4,6-triyl)tris(N,N-bis(4-methoxyphenyl)aniline) (BPT-3TPA):

[0097]

[0098] In a round-bottom flask, BPT-TPA-2BR (0.53 g, 0.8 mmol), OMETPA-BPIN (1.8 g, 4.18 mmol), Pd(PPh3)4 (0.02 g, 0.016 mmol), and tetrahydrofuran solvent (35 mL) were added, followed by an aqueous solution of sodium carbonate (1.77 g, 2 M). The reaction was refluxed under nitrogen for 12 hours. The resulting mixture was quenched with distilled water (3 mL) and then extracted with ethyl acetate (300 mL). The crude product was dried over anhydrous magnesium sulfate. BPT-3TPA was obtained by vacuum distillation and purified by silica gel column chromatography in 80% yield. 1 H NMR(500MHz,Methylene Chloride-d2)δ7.49–6.87(m,36H),3.83(s,18H).

[0099] Table 1

[0100]

[0101] Depend on Figure 1 The cyclic voltammetry curves yielded HOMO values ​​of -5.00, -4.99, -5.03, and -5.11 eV for the four materials. Figure 2 The UV-Vis absorption spectra of the coated materials yielded band gaps of 2.44 eV, 2.61 eV, 2.57 eV, and 2.62 eV for the four groups of materials, with peak positions (λ...). onset The wavelengths are 507 nm, 475 nm, 483 nm, and 474 nm, respectively, and the maximum absorption peak (λ) after coating is... max filmThe corresponding nm wavelengths are 428nm, 413nm, 409nm, and 407nm, respectively. Figure 3 The thermogravimetric analysis curves can be used to obtain the decomposition temperatures (T) of the four groups of materials. d The temperatures were 417, 400, 374, and 432℃, respectively. Figure 4 The differential scanning calorimetry (DSC) curves can be used to obtain the glass transition temperatures (T) of the four groups of materials. g The test data obtained from the cyclic voltammetry curves, UV-Vis absorption spectra, thermogravimetric analysis curves, and differential scanning calorimetry curves of the four groups of materials at 55℃, 88℃, 100℃, and 78℃ are shown in Table 1.

Claims

1. A hole transport material based on thiopheno[3,2-b]indole, characterized in that, The structural formula is: 。 2. The method for synthesizing hole transport materials based on thiopheno[3,2-b]indole according to claim 1, characterized in that, Includes the following steps: (1) Under nitrogen protection, 1,4-dibromo-2-nitrobenzene and 2-tributylmethyltinylthiophene undergo a Still coupling reaction at 100-110℃ catalyzed by tetrakis(triphenylphosphine)palladium to produce 2-(4-bromo-2-nitrobenzene)thiophene. ； (2) Using chlorobenzene as a solvent, 2-(4-bromo-2-nitrophenyl)thiophene reacts with triphenylphosphine as a catalyst at 135-145℃ to generate 6-bromo-4H-thiopheno[3,2-b]indole. ； (3) In DME and potassium hydroxide aqueous solution, 6-bromo-4H-thieno[3,2-b]indole, 4-iodo-N,N-bis(4-methoxyphenyl)aniline, cuprous iodide and 1,10-phenanthroline react at 90~95℃ to generate 4-(6-bromo-4H-thieno[3,2-b]indole-4-yl)-N,N-bis(4-methoxyphenyl)aniline. ； (4) Using tetrahydrofuran as a solvent, the product from step (3) and N-bromosuccinimide react at 0°C to generate an intermediate. ； (5) In the presence of tetrahydrofuran and sodium carbonate aqueous solution, the intermediate and 4-boron ester-4',4'-dimethoxytriphenylamine react at 75-80 °C under the catalysis of tetratriphenylphosphine palladium to generate the target product. 。 3. The synthesis method according to claim 2, characterized in that, In step (1), the molar ratio of 4-dibromo-2-nitrobenzene to 2-tributyltinylthiophene is 1:0.

9.

4. The synthesis method according to claim 2, characterized in that, In step (2), the molar ratio of 2-(4-bromo-2-nitrophenyl)thiophene to triphenylphosphine is 1:

5.

5. The synthesis method according to claim 2, characterized in that, In step (3), the volume ratio of ethylene glycol dimethyl ether to water is 1:

2.

6. The synthesis method according to claim 2, characterized in that, In step (5), the volume ratio of tetrahydrofuran to water is 1:

1.

7. The application of the hole transport material based on thiopheno[3,2-b]indole according to claim 1 in perovskite solar cells.

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