An organic hole transport material based on a bis-spirofluorene structure that can be green-processed, its synthesis method and application

Abstract

The present invention belongs to the field of organic optoelectronic materials, and discloses an organic hole transporting material based on a bis-spirofluorene structure that can be green-processed, its synthesis method, and its application in perovskite solar cells. The present invention uses dispiro[oxanthene-9,6'-indeno[1,2-b]fluorene-12',9''-oxanthene] as the core, and by introducing different side chains and electron-donating groups on the outer sides of the two oxanthenes and the end groups of the core, the purification process, solubility, and optoelectronic properties of the molecule are regulated. Such materials have the advantages of simple synthesis and purification processes, high hole transport performance, and excellent solubility, and some can even be purified without column chromatography and prepared for the hole transport layer of the battery by green solvent processing. The perovskite solar cells prepared based on such hole transporting materials have the advantages of low cost, high efficiency, energy conservation, and environmental protection.

Description

Technical Field

[0001] The present invention relates to the field of organic optoelectronic materials, and particularly to an organic hole transport material based on a bis-spirofluorene structure that can be green-processed, its synthesis method, and its application in perovskite solar cells. Background Art

[0002] In recent years, perovskite solar cells have become one of the most promising photovoltaic technologies due to many advantages such as low material cost, strong solution processability, and excellent optoelectronic performance. At present, the highest power conversion efficiency of single-junction perovskite solar cells has reached 25.7%, which is comparable to that of crystalline silicon solar cells. Like most organic optoelectronic devices, perovskite solar cells exhibit a typical multi-layer sandwich device structure, and a charge transport layer is introduced between the photoactive layer and the electrode as a buffer layer to improve interfacial charge transport. The hole transport layer plays a variety of key roles in determining the device performance, such as hole extraction and transport, improving surface defects of the photoactive layer, suppressing ion migration, and reducing non-radiative recombination losses (Chem. Soc. Rev. 2020, 49(13), 4496-4526; Energy Environ. Sci. 2019, 12(1), 396-409).

[0003] So far, the organic small molecule Spiro-OMeTAD with a single spirofluorene structure has been a commonly used hole transport material in perovskite solar cells, achieving relatively high power conversion efficiency (Science 2022, 377(6605), 531-534). However, the spirofluorene core of Spiro-OMeTAD involves multiple-step ring-closing reactions, and the yields are generally low, resulting in high synthesis costs, which poses a major challenge to the commercial application of spiro-based hole transport materials (Chem. Rev. 2007, 107(4), 1011-1065). Organic polymers such as poly(triphenylamine) PTAA have also been used as hole transport materials in perovskite solar cells, but their efficiency is much lower than that of Spiro-OMeTAD, and the differences between polymer batches affect reproducibility (Adv. Energy Mater. 2014, 4(16), 1400768). On the other hand, the column chromatography method used to purify these organic molecules is not only time-consuming and laborious but also not suitable for the manufacture of large-scale kilogram-scale products. More importantly, these high-performance organic hole transport materials must be processed using toxic solvents such as chlorobenzene or toluene when applied to perovskite solar cells (ACS Energy Lett. 2022, 7(3), 1154-1177), which is not advisable for commercial device preparation. Although a few low-cost or green-solvent-processable hole transport materials have been reported, almost all organic hole transport materials are difficult to avoid column chromatography purification (Chem. Soc. Rev. 2018, 47(23), 8541-8571). Therefore, developing new hole transport materials that are easy to synthesize, free of column chromatography purification, and processable with green solvents is crucial for achieving efficient and low-cost perovskite solar cells and is also a huge challenge. Summary of the Invention

[0004] Aiming at the deficiencies of the current technology of organic hole transport materials, the present invention provides a synthesis method of an organic hole transport material based on a bis-spirofluorene structure that can be green-processed and its application in perovskite solar cells. The hole transport material uses bis-spiro[9H-xanthene-9,6'-indeno[1,2-b]fluorene-12',9”-xanthene] as the core, and different side chains and electron-donating groups are introduced on the outer sides of the two xanthenes and the end groups of the core to realize the regulation of the purification process, solubility, and optoelectronic properties of the molecule. Such materials have simple synthesis and purification processes, high hole transport performance, and excellent solubility, and some can even be prepared for the hole transport layer of the battery without column chromatography purification and with green solvents. Therefore, the perovskite solar cells prepared using such hole transport materials have the advantages of low cost, high efficiency, energy conservation, and environmental protection.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A hole transport material based on a bis-spirofluorene structure, characterized in that: using bis-spiro[xanthene-9,6'-indeno[1,2-b]fluorene-12',9”-xanthene] as the core, connected to different electron-donating groups at both ends, and introducing different side chain groups outside the two xanthenes of the core to construct a novel hole transport material with a bis-spirofluorene structure. The hole transport material has the following chemical structural general formula (I):

[0007]

[0008] In formula (I),

[0009] R1 is an alkyl group or an oxaalkyl group;

[0010] X is a residue of a diphenylamine derivative or a triphenylamine derivative, specifically one of the following structures:

[0011]

[0012] Among them, the R group is independently selected from any one of hydrogen, methyl, methoxy or methylthio, and the dotted line indicates the group connection position.

[0013] The synthesis method of the hole transport material using bis-spiro[xanthene-9,6'-indeno[1,2-b]fluorene-12',9”-xanthene] as the core is as follows: 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione and resorcinol undergo a cyclization reaction to obtain compound 1; compound 1 undergoes an alkylation reaction to obtain compound 2; compound 2 undergoes a coupling reaction with an electron-donating group, and finally obtains the hole transport material DiSFX using bis-spiro[xanthene-9,6'-indeno[1,2-b]fluorene-12',9”-xanthene] as the core. The specific steps are as follows:

[0014] (i) Add the reactants 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione, resorcinol and p-toluenesulfonic acid into a clean and dry reaction vessel. After the mixture is stirred evenly, heat it to 100 - 120 °C and react for 24 - 48 h. After the reaction is completed, cool it to room temperature. Add water to the reaction solution and continue to stir at room temperature for 1 - 3 h. At this time, a large amount of orange-yellow precipitate appears in the mixed solution. Use a vacuum pump to filter and collect the filter cake. Dissolve the obtained solid in ethanol, filter again, and collect the filtrate to remove insoluble impurities. The filtrate is evaporated under reduced pressure to obtain a solid product, which is dried in vacuo to obtain compound 1;

[0015] (ii) Add compound 1, potassium carbonate and ethanol solvent into a clean container, stir for 1 - 2 h at room temperature, then slowly inject organic bromide R1Br into the container, raise the temperature of the solution to 90 °C, and react for 24 - 48 h. After the reaction is completed, remove the solvent in the reaction solution by evaporation under reduced pressure, wash the obtained solid with water and ethanol in sequence, and dry it under vacuum to obtain compound 2; wherein, R1 is an alkyl group or an oxaalkyl group;

[0016] (iii) Add compound 2, diphenylamine derivative or triphenylamine derivative, tetrakis(triphenylphosphine)palladium, saturated aqueous potassium carbonate solution and toluene solvent into a clean and dry reaction container, stir evenly under nitrogen protection, then heat the reaction to 100 - 120 °C and react for 24 - 48 h. After the reaction is completed, cool to room temperature, pour the reaction solution into water to quench it, then extract it several times with ethyl acetate, collect the upper organic phase and remove the solvent under reduced pressure, and purify the obtained solid by recrystallization or column chromatography. When R1 is an alkyl group, column chromatography is required for purification; when R1 is an alkoxy group, recrystallization can be used for purification. After the product is further dried under vacuum, a hole transporting material DiSFX with spiro[fluorene-9,6'-indeno[1,2-b]fluorene-12',9”-fluorene] as the core is obtained. Wherein, X is the residue of diphenylamine derivative or triphenylamine derivative.

[0017] The synthesis process is as follows:

[0018]

[0019] In step (i), the molar ratio of 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione, resorcinol and p-toluenesulfonic acid is 1:10:0.2; the reaction concentration of 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione is 0.08 - 0.15 mol / L.

[0020] In step (i), the volume ratio of the reaction solution to water is 1:1 - 1.5.

[0021] In step (ii), the molar ratio of compound 1:R1Br:potassium carbonate is 1:7.5:15; the reaction concentration of compound 1 is 0.02 - 0.04 mol / L.

[0022] In step (iii), the molar ratio of compound 2:diphenylamine derivative or triphenylamine derivative:tetrakis(triphenylphosphine)palladium is 1:2.2:0.1; the reaction concentration of compound 2 is 0.04 - 0.08 mol / L.

[0023] In step (iii), the concentration of the saturated aqueous potassium carbonate solution is 8 mol / L.

[0024] In step (iii), the volume ratio of toluene to saturated potassium carbonate aqueous solution is 2 - 3:1.

[0025] The hole transporting material with dithieno[3,2-b:2',3'-d]thiophene-2,6-diyl-9,9-dimethylxanthene-4,5-diyl as the core synthesized in the present invention is applied to a normal structure perovskite solar cell.

[0026] The specific structure of the normal structure perovskite solar cell is FTO / TiO2 / SnO2 / (FAPbI3) 0.99 (MAPbBr3) 0.01 perovskite / hole transporting layer / Au. Among them, the specific preparation process of the hole transporting layer is as follows:

[0027] (1) The hole transporting material DiSFX and additives 4-tert-butylpyridine (TBP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are configured into a solution of chlorobenzene or 2-methoxytoluene with a certain concentration.

[0028] (2) The prepared DiSFX precursor solution is spin-coated on the (FAPbI3) 0.99 (MAPbBr3) 0.01 perovskite layer to obtain the hole transporting layer.

[0029] In step (1), for the DiSFX material with an alkyl side chain as R1, only chlorobenzene can be used as the solvent; for the DiSFX material with an alkoxy side chain as R1, chlorobenzene or non-toxic 2-methoxytoluene can be used as the solvent.

[0030] The present invention has the following advantages:

[0031] The hole transporting material DiSFX provided by the present invention has the advantages of simple synthesis process, convenient purification process, high reaction yield, etc. Some can even be purified without column chromatography and processed with green solvents, thus realizing the synthesis of organic hole transporting materials without column chromatography at low cost and the green preparation of the hole transporting layer in perovskite solar cells. In addition, DiSFX also has excellent solubility and hole transporting performance, meeting the primary conditions for being used as the hole transporting layer of an efficient perovskite solar cell. Therefore, the present invention opens up a new way for the large-scale and environmentally friendly manufacture of efficient and low-cost perovskite solar cells. Description of the Drawings

[0032] Figure 1 It is the molecular structure of the hole transporting materials DiSFX-C6 and DiSFX-OC6 synthesized in Examples 1 and 2 of the present invention.

[0033] Figure 2 It is the hole mobility test chart of the hole transporting materials DiSFX-C6 and DiSFX-OC6 synthesized in Examples 1 and 2 of the present invention.

[0034] Figure 3 The film morphology diagram shows DiSFX-C6 dissolved in chlorobenzene and DiSFX-OC6 dissolved in chlorobenzene or 2-methoxytoluene and spin-coated on the perovskite film.

[0035] Figure 4 The atomic force microscope diagram shows DiSFX-C6 dissolved in chlorobenzene and DiSFX-OC6 dissolved in chlorobenzene or 2-methoxytoluene and spin-coated on the perovskite film.

[0036] Figure 5 a) The J-V curve diagram of perovskite solar cells prepared with the compounds DiSFX-C6 and DiSFX-OC6 synthesized in Examples 1 and 2 of the present invention in different solvents; b) The IPCE diagram of perovskite solar cells prepared with DiSFX-C6 and DiSFX-OC6 in different solvents. Detailed implementation manners

[0037] The following further illustrates the present invention in conjunction with specific implementation examples, so that those skilled in the art can better understand the present invention. However, the protection scope of the present invention is not limited to the following examples, and the scope of rights of the present invention shall be defined by the claims.

[0038] Example 1:

[0039] Synthesis of hole transport material DiSFX-C6:

[0040]

[0041] (i) Add the reactants 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione (4.37 g, 10.00 mmol), resorcinol (11.00 g, 100.00 mmol), p-toluenesulfonic acid (0.34 g, 2.00 mmol) and 100 mL of toluene solvent into a clean and dry reaction vessel. After the mixture is stirred evenly, heat it to 120 °C and react for 24 h. After the reaction is completed, cool it to room temperature. Add 100 mL of water to the reaction solution and continue to stir at room temperature for 1 h. At this time, a large amount of orange-yellow precipitate appears in the mixed solution. Use a vacuum pump to filter and collect the filter cake. Dissolve the obtained solid in ethanol, filter again, and collect the filtrate to remove insoluble impurities. The filtrate is evaporated under reduced pressure to obtain a solid product, which is dried in vacuum to obtain Compound 1 (7.74 g, yield: 96%); 1HNMR(400MHz,DMF-d7)δ9.97(s,4H),7.99(d,J=8.2Hz,2H),7.86(s,2H),7.54(dd,J=8.2,1.9Hz,2H),7.25(d,J=1.8Hz,2H),6.78(d,J=2.4Hz,4H),6.43(dd,J=8.6,2.5Hz,4H),6.27(d,J=8.5Hz,4H).

[0042] (ii) In a clean container, add compound 1 (0.80 g, 1.00 mmol), potassium carbonate (2.07 g, 15.00 mmol) and 50 mL of ethanol solvent. Stir the mixture at room temperature for 1 h, then slowly inject bromohexane (1.24 g, 7.50 mmol) into the container. Raise the temperature of the solution to 90 °C and react for 24 h. After the reaction is completed, remove the solvent in the reaction solution by evaporation under reduced pressure. Wash the obtained solid with water and ethanol successively, and dry it under vacuum to obtain compound 2 (1.04 g, yield: 91%); 1 H NMR(400MHz,CDCl3)δ7.42(d,J=12.5Hz,6H),7.23(s,2H),6.79(d,J=2.5Hz,4H),6.43(dd,J=8.8,2.6Hz,4H),6.32(d,J=8.7Hz,4H),3.98(t,J=6.5Hz,8H),1.80(p,J=6.7Hz,8H),1.52–1.30(m,24H),0.98–0.86(m,12H).

[0043] (iii) In a clean and dry reaction container, add compound 2 (0.91 g, 0.8 mmol), 4,4'-dimethoxytriphenylamine-4''-boronic acid pinacol ester (0.76 g, 1.76 mmol), tetrakis(triphenylphosphine)palladium (0.09 g, 0.08 mmol), 7 mL of saturated potassium carbonate aqueous solution and 20 mL of toluene solvent. Stir evenly under nitrogen protection, then heat the reaction to 100 °C and react for 24 h. After the reaction is completed, cool to room temperature, pour the reaction solution into water to quench, then extract with ethyl acetate several times. Collect the upper organic phase and remove the solvent under reduced pressure. Separate and purify the obtained solid by column chromatography, using petroleum ether / dichloromethane (1:1 vol / vol) as the eluent. Dry under vacuum to obtain a hole transporting material in the form of a yellow-green powder, labeled DiSFX-C6 (1.18 g, yield: 93%). 1HNMR (400 MHz, CDCl3) δ 7.61 (t, J = 8.1 Hz, 4H), 7.48 (s, 4H), 7.34 (s, 2H), 7.09 (d, J = 8.4 Hz, 8H), 6.92–6.78 (m, 18H), 6.41 (d, J = 1.4 Hz, 8H), 3.97 (t, J = 6.5 Hz, 8H), 3.81 (d, J = 8.8 Hz, 12H), 1.84–1.74 (m, 8H), 1.53–1.42 (m, 8H), 1.35 (d, J = 2.6 Hz, 16H), 0.93 (t, J = 4.6 Hz, 12H). 13 C NMR (151 MHz, THF) δ 159.22, 156.55, 156.10, 152.25, 151.45, 148.18, 140.84, 140.63, 140.41, 139.72, 138.21, 135.54, 132.75, 128.65, 127.06, 126.87, 126.05, 125.47, 122.85, 120.88, 120.16, 118.33, 116.96, 116.77, 114.49, 114.37, 110.73, 101.46, 82.93, 67.73, 54.59, 54.57, 53.33, 31.57, 29.21, 25.74, 22.55, 13.41. HR-MS: (ESI) m / z: C 108 H 108 N2O 10 , calculated value 1593.8082; measured value 1593.8004.

[0044] The above-synthesized hole-transporting material DiSFX-C6 was applied to a perovskite solar cell, and its preparation process was as follows:

[0045] The etched FTO glass was successively cleaned in an ultrasonic bath with Hellmanex (2%, ultrapure water), ultrapure water, acetone, and isopropanol for 20 minutes each, and then further surface-treated with ultraviolet ozone cleaning for 15 minutes. A dense TiO2 layer was deposited on top of the FTO glass using spray pyrolysis (with O2 as the carrier gas): an ethanol solution of 0.2 M diisopropyl bis(acetylacetonato)titanate was sprayed at a low speed onto the FTO glass substrate heated to 450 °C. After spray pyrolysis, the FTO / c-TiO2 substrate was held at 450 °C for 1 h and then cooled to ambient temperature to obtain a TiO2 dense layer with a thickness of approximately 20 nm. 15 wt% SnO2 colloid was diluted 25 times with ultrapure water, 0.4 mg / mL of polyacrylic acid was added, and then stirred at 80 °C for 2 hours. The resulting solution was spin-coated onto the c-TiO2 layer, controlling the rotation speed at 4000 rpm and the spin-coating time at 30 s, and then annealed on a heated plate at 150 °C for 30 min. The following operating steps (except for solution preparation and metal electrode evaporation in a nitrogen environment) were all completed in an air glove box with an ambient humidity of 25% and a temperature of 25 °C. Lead iodide (PbI2), formamidinium hydroiodide (FAI), methylammonium hydrochloride (MACl), methylammonium lead bromide (MAPbBr3) (molar ratio 1.1:1:0.36:0.01) were dissolved in a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide (volume ratio 8:1) and stirred at room temperature for 6 h. The prepared perovskite precursor solution was spin-coated onto the FTO / c-TiO2 / SnO2 substrate, controlling the rotation speed in the first stage at 1000 rpm and the spin-coating time at 10 s, and in the second stage at 6000 rpm and the spin-coating time at 30 s. At the 10th second from the end of the second-stage spin-coating, 200 μL of chlorobenzene was uniformly dropped onto the film, and then the film was annealed at 100 °C for 1 h. After the perovskite film was cooled to room temperature, a chlorobenzene solution of the hole transport material DiSFX-C6 (50 mg of DiSFX-C6, 22 μL of a 520 mg / mL acetonitrile solution of LiTFSI, 37 μL of TBP dissolved in 1 mL of chlorobenzene) was spin-coated onto the surface of the perovskite film, controlling the rotation speed at 5000 rpm and the spin-coating time at 30 s. Finally, a 100 nm Au electrode was vacuum-evaporated above the DiSFX-C6 layer, and the photoactive area of the device was 0.0625 cm 2 。

[0046] Example 2:

[0047] Synthesis of hole transport material DiSFX-OC6:

[0048]

[0049] (i) Add the reactants 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione (4.37 g, 10.00 mmol), resorcinol (11.00 g, 100.00 mmol), p-toluenesulfonic acid (0.34 g, 2.00 mmol) and 100 mL of toluene solvent into a clean and dry reaction vessel. After the mixture is stirred evenly, heat it to 120 °C and react for 24 h. After the reaction is completed, cool it to room temperature. Add 100 mL of water to the reaction solution and continue to stir for 1 h at room temperature. At this time, a large amount of orange-yellow precipitate appears in the mixed solution. Use a vacuum pump to filter and collect the filter cake. Dissolve the obtained solid in ethanol, filter again, and collect the filtrate to remove insoluble impurities. The filtrate is evaporated under reduced pressure to obtain a solid product, which is dried in vacuo to obtain Compound 1 (7.74 g, yield: 96%); 1 HNMR(400MHz,DMF-d7)δ9.97(s,4H),7.99(d,J=8.2Hz,2H),7.86(s,2H),7.54(dd,J=8.2,1.9Hz,2H),7.25(d,J=1.8Hz,2H),6.78(d,J=2.4Hz,4H),6.43(dd,J=8.6,2.5Hz,4H),6.27(d,J=8.5Hz,4H).

[0050] (ii) Add Compound 1 (0.80 g, 1.00 mmol), potassium carbonate (2.07 g, 15.00 mmol) and 50 mL of ethanol solvent into a clean container. Stir the mixture at room temperature for 1 h, and then slowly inject 1-bromo-2-(2-methoxyethoxy)ethane (1.37 g, 7.50 mmol) into the container. Raise the temperature of the solution to 90 °C and react for 24 h. After the reaction is completed, remove the solvent in the reaction solution by evaporation under reduced pressure. The obtained solid is washed successively with water and ethanol, and dried in vacuo to obtain Compound 2 (1.15 g, yield: 95%); 1 H NMR(400MHz,CDCl3)δ7.45–7.32(m,6H),7.19(d,J=1.7Hz,2H),6.78(d,J=2.5Hz,4H),6.43(dd,J=8.7,2.6Hz,4H),6.30(d,J=8.7Hz,4H),4.14(t,J=4.9Hz,8H),3.85(t,J=4.8Hz,8H),3.75–3.65(m,8H),3.61–3.51(m,8H),3.38(s,12H).

[0051] (iii) In a clean and dry reaction vessel, add compound 2 (0.97 g, 0.8 mmol), 4,4'-dimethoxytriphenylamine-4''-boronic acid pinacol ester (0.76 g, 1.76 mmol), tetrakis(triphenylphosphine)palladium (0.09 g, 0.08 mmol), 7 mL of saturated potassium carbonate aqueous solution and 20 mL of toluene solvent. Stir evenly under nitrogen protection, and then heat the reaction to 100 °C for 24 h. After the reaction is completed, cool to room temperature, pour the reaction solution into water to quench, and then extract with ethyl acetate several times. The organic layer is filtered through diatomaceous earth and evaporated under reduced pressure. The obtained solid is separated and purified by recrystallization method, and petroleum ether / ethyl acetate (1:10 vol / vol) is used as the recrystallization solvent. Vacuum dry to obtain a hole transport material as a yellow-green solid, labeled as DiSFX-OC6 (1.09 g, yield: 82%). 1 HNMR(600MHz,THF-d8)δ7.76(d,J=8.0Hz,2H),7.61(s,2H),7.56(dd,J=8.1,1.7Hz,2H),7.36–7.32(m,4H),7.31(d,J=1.7Hz,2H),7.02–6.98(m,8H),6.90–6.87(m,4H),6.85(d,J=2.3Hz,4H),6.84–6.81(m,8H),6.45–6.40(m,8H),4.12(dd,J=5.8,4.2Hz,8H),3.80(dd,J=5.7,4.2Hz,8H),3.76(s,12H),3.64(dd,J=5.8,4.2Hz,8H),3.50(dd,J=5.7,4.3Hz,8H),3.31(s,12H).13C NMR(151MHz,THF)δ159.04,156.52,156.10,156.07,152.22,148.18,140.85,140.65,139.75,138.19,132.75,128.68,127.07,126.05,125.50,122.85,120.88,120.19,117.19,116.79,114.38,110.83,101.70,71.98,70.55,69.46,67.63,58.00,54.58,53.34.HR-MS:(ESI)m / z:C 104 H 100 N2O 18 , calculated value 1665.7050; measured value 1665.6970.

[0052] Apply the above-synthesized hole transport material DiSFX-OC6 to perovskite solar cells, and its preparation process is as follows:

[0053] The etched FTO glass was successively cleaned in an ultrasonic bath with Hellmanex (2%, ultrapure water), ultrapure water, acetone, and isopropanol for 20 minutes each, and then further surface-treated with ultraviolet ozone cleaning for 15 minutes. A dense TiO2 layer was deposited on top of the FTO glass using spray pyrolysis (with O2 as the carrier gas): an ethanol solution of 0.2 M diisopropyl bis(acetylacetonato)titanate was sprayed at a low speed onto the FTO glass substrate heated to 450 °C. After spray pyrolysis, the FTO / c-TiO2 substrate was held at 450 °C for 1 h and then cooled to ambient temperature to obtain a TiO2 dense layer with a thickness of approximately 20 nm. 15 wt% of SnO2 colloid was diluted 25 times with ultrapure water, 0.4 mg / mL of polyacrylic acid was added, and then stirred at 80 °C for 2 h. The resulting solution was spin-coated onto the c-TiO2 layer, with the rotation speed controlled at 4000 rpm and the spin-coating time at 30 s, and then annealed on a hot plate at 150 °C for 30 min. The following operating steps (except for solution preparation and metal electrode evaporation in a nitrogen environment) were all completed in an air glove box with an ambient humidity of 25% and a temperature of 25 °C. Lead iodide (PbI2), formamidinium hydrogen iodide (FAI), methylammonium hydrochloride (MACl), methylammonium lead bromide (MAPbBr3) (molar ratio 1.1:1:0.36:0.01) were dissolved in a mixed solvent of N,N-dimethylformamide and dimethyl sulfoxide (volume ratio 8:1) and stirred at room temperature for 6 h. The prepared perovskite precursor solution was spin-coated onto the FTO / c-TiO2 / SnO2 substrate, with the rotation speed controlled at 1000 rpm for the first stage and the spin-coating time at 10 s, and 6000 rpm for the second stage and the spin-coating time at 30 s. At the 10th second from the end of the second-stage spin-coating, 200 μL of chlorobenzene was uniformly dropped onto the film, and then the film was annealed at 100 °C for 1 h. For the hole transport material DiSFX-OC6, solutions can be prepared using chlorobenzene or 2-methoxytoluene, namely, the chlorobenzene solution of DiSFX-OC6 (50 mg of DiSFX-OC6, 22 μL of a 520 mg / mL acetonitrile solution of LiTFSI, 37 μL of TBP dissolved in 1 mL of chlorobenzene) and the 2-methoxytoluene solution of DiSFX-OC6 (37 mg of DiSFX-OC6, 22 μL of a 520 mg / mL acetonitrile solution of LiTFSI, 37 μL of TBP dissolved in 1 mL of 2-methoxytoluene). When preparing the hole transport layer with the chlorobenzene solution of DiSFX-OC6, the spin-coating rotation speed was controlled at 5000 rpm and the spin-coating time at 30 s; when preparing the hole transport layer with the 2-methoxytoluene solution of DiSFX-OC6, the spin-coating rotation speed was controlled at 4000 rpm and the spin-coating time at 30 s. Finally, a 100-nm Au electrode was vacuum-evaporated above the DiSFX-OC6 layer, and the photoactive area of the device was 0.0625 cm2 .

[0054] Figure 1 These are the molecular structures of the hole transport materials DiSFX-C6 and DiSFX-OC6 synthesized in Examples 1 and 2 of the present invention.

[0055] Figure 2 These are the hole mobility test graphs of the hole transport materials DiSFX-C6 and DiSFX-OC6 synthesized in Examples 1 and 2 of the present invention. As can be seen from the figure, both DiSFX hole transport materials have high charge transport performance. The hole mobilities of DiSFX-C6 and DiSFX-OC6 are 1.62×10 -4 cm 2 ·v -1 ·s -1 and 1.67×10 -4 cm 2 ·v -1 ·s -1 .

[0056] Figure 3 These are the film morphology graphs of DiSFX-C6 dissolved in chlorobenzene and DiSFX-OC6 dissolved in chlorobenzene or 2-methoxytoluene and spin-coated on the perovskite film. As can be seen from the film morphology graph, the films of the hole transport materials DiSFX-C6 and DiSFX-OC6 can completely cover the perovskite, and the film prepared by dissolving DiSFX-OC6 in 2-methoxytoluene has fewer pits than that prepared by dissolving it in chlorobenzene.

[0057] Figure 4 These are the atomic force microscopy graphs of DiSFX-C6 dissolved in chlorobenzene and DiSFX-OC6 dissolved in chlorobenzene or 2-methoxytoluene and spin-coated on the perovskite film. As can be seen from the image, the surface roughness of the DiSFX-OC6 hole transport layer prepared using 2-methoxytoluene as the solvent is the smallest, indicating that using 2-methoxytoluene as the solvent to prepare the DiSFX-OC6 hole transport layer not only avoids the toxic pollution of chlorobenzene but also improves the film-forming quality of the hole transport material DiSFX-OC6.

[0058] Figure 5 a) These are the J-V curves of the perovskite solar cells prepared with the compounds DiSFX-C6 and DiSFX-OC6 synthesized in Examples 1 and 2 of the present invention in different solvents; b) These are the IPCE graphs of the perovskite solar cells prepared with DiSFX-C6 and DiSFX-OC6 in different solvents. As can be seen from the figure, using chlorobenzene as the solvent, the perovskite solar cells with DiSFX-C6 and DiSFX-OC6 as the hole transport materials obtained 22.18% (J SC = 24.86 mA·cm -2 , VOC = 1.14 V, FF = 78.21%) and 21.37% (J SC = 24.85 mA·cm -2 , V OC = 1.11 V, FF = 77.25%). The perovskite solar cells using 2-methoxytoluene as the solvent and DiSFX-OC6 as the hole transport material achieved a power conversion efficiency of 23.55% (J SC = 25.02 mA·cm -2 , V OC = 1.15 V, FF = 81.73%). In addition, the perovskite solar cells based on the hole transport materials DiSFX-C6 and DiSFX-OC6 had an IPCE value above 80% in the 400–800 nm region, indicating good power conversion ability.

Claims

1. An organic hole transport material based on a bis-spirofluorene structure and capable of green processing, characterized in that, The general chemical structure formula is: Among them, R1 is an alkyl group or an oxaalkyl group; X is the residue of a diphenylamine derivative or a triphenylamine derivative, specifically one of the following structures: The R group is independently selected from any one of hydrogen, methyl, methoxy or methylthio group, and the dotted line indicates the group connection position.

2. The synthesis method of the organohole transporting material based on the bis-spirofluorene structure that can be green-processed according to claim 1, characterized in that (i) Add the reactants 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione, resorcinol and p-toluenesulfonic acid into a clean and dry reaction vessel. After the mixture is stirred evenly, heat the reaction to the end, then cool to room temperature. Add water to the reaction solution and continue to stir at room temperature for a certain time. At this time, a large amount of orange-yellow precipitate appears in the mixed solution. Use a vacuum pump to filter, collect the filter cake, dissolve the obtained solid in ethanol, filter again, and collect the filtrate to remove insoluble impurities. The filtrate is evaporated under reduced pressure to obtain a solid product, which is dried in vacuo to obtain Compound 1. The structural formula of Compound 1 is: (ii) Add Compound 1, potassium carbonate and ethanol solvent into a clean container, stir at room temperature for a certain time, then slowly inject the organic bromide R1Br into the container, raise the solution temperature to the reaction temperature. After the reaction is completed, remove the solvent in the reaction solution by evaporation under reduced pressure. The obtained solid is washed successively with water and ethanol, and dried in vacuo to obtain Compound 2. The structural formula of Compound 2 is: Among them, R1 is an alkyl group or an oxaalkyl group; (iii) Add Compound 2, a diphenylamine derivative or a triphenylamine derivative, tetrakis(triphenylphosphine)palladium, saturated aqueous potassium carbonate solution and toluene solvent into a clean and dry reaction vessel, stir evenly under nitrogen protection, then carry out a heating reaction. After the reaction is completed, cool to room temperature, pour the reaction solution into water to quench, then add ethyl acetate to extract several times, collect the upper organic phase and remove the solvent under reduced pressure. The obtained solid is separated and purified by recrystallization or column chromatography, and dried in vacuo to obtain the hole transporting material DiSFX with bis-spiro[oxanthene-9,6'-indeno[1,2-b]fluorene-12',9”-oxanthene] as the core, that is, the organohole transporting material based on the bis-spirofluorene structure that can be green-processed. The structural formula is: Among them, X is the residue of a diphenylamine derivative or a triphenylamine derivative.

3. The synthesis method according to claim 2, wherein In step (i), The molar ratio of 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione, resorcinol and p-toluenesulfonic acid is 1:10:0.2; the reaction concentration of 2,8-dibromoindeno[1,2-b]fluorene-6,12-dione is 0.08 - 0.15 mol / L; The volume ratio of the reaction solution to water is 1:1 - 1.

5.

4. The synthesis method according to claim 2, wherein In step (i), the heating reaction temperature is 100 - 120 °C, and the reaction time is 24 - 48 h; after adding water to the reaction solution, the stirring time at room temperature is 1 - 3 h.

5. The synthesis method according to claim 2, characterized in that, In step (ii), the molar ratio of Compound 1:R1Br:potassium carbonate is 1:7.5:15; the reaction concentration of Compound 1 is 0.02 - 0.04 mol / L.

6. The synthesis method according to claim 2, characterized in that, In step (ii), the stirring time is 1 - 2 h at room temperature, the reaction temperature is 90 °C, and the reaction time is 24 - 48 h.

7. The synthesis method according to claim 2, characterized in that, In step (iii), the molar ratio of compound 2: diphenylamine derivative or triphenylamine derivative: palladium tetrakistriphenylphosphine is 1:2.2:0.1; the reaction concentration of compound 2 is 0.04 - 0.08 mol / L; the concentration of saturated potassium carbonate aqueous solution is 8 mol / L.

8. The synthesis method according to claim 2, characterized in that, In step (iii), the volume ratio of the amounts of toluene and saturated potassium carbonate aqueous solution used is 2 - 3:

1.

9. The synthesis method according to claim 2, wherein In step (iii), the reaction is heated to 100 - 120 °C and reacted for 24 - 48 h; Among them, when R1 is an alkyl group, the obtained solid needs to be purified by column chromatography; When R1 is an oxaalkyl group, the obtained solid is purified by recrystallization.

10. Using the green processable organic hole transport material based on the bispirofluorene structure as claimed in claim 1 to prepare an inverted perovskite solar cell FTO / TiO2 / SnO2 / (FAPbI3) 0.99 (MAPbBr3) 0.01 Uses of perovskite / hole transport layer / Au.

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