Asymmetric self-assembled monomolecular layer material and application thereof in perovskite solar cell

Abstract

The invention belongs to the technical field of application of organic semiconductor functional materials and solar cell devices, and discloses an asymmetric self-assembled monomolecular layer material and application thereof in a perovskite solar cell. The asymmetric self-assembled monomolecular layer hole transport material containing the 9, 9-dimethyl-N-phenyl-fluorene unit is obtained by taking the 9, 9-dimethyl-N-phenyl-fluorene unit as a bottom end group, a diphenylamine phenyl group as a connecting unit and cyanomethylphosphoric acid as an anchoring group and a passivation group. When the material is applied to a perovskite solar cell as a hole transport layer, the hole extraction and transmission performance of the material can be effectively improved, and cyanomethyl phosphoric acid in the material can effectively improve the crystallization performance of perovskite on a self-assembled monomolecular layer. The photoelectric conversion efficiency of more than 23% and more than 19% can be respectively obtained in the conventional perovskite solar cell with the band gap of 1.52 eV and the perovskite solar cell with the wide band gap of 1.77 eV, and the commercialization cost of the perovskite solar cell technology can be further reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic semiconductor functional materials and solar cell device applications, and particularly relates to a self-assembled monolayer hole transport material containing 9,9-dimethyl-N-phenyl-fluorene units, a synthesis method thereof, and an application in perovskite solar cells. Background Art

[0002] Perovskite solar cells have become a hot research topic in both the industrial and academic fields due to their advantages such as low cost, simple preparation process, adjustable bandgap, and high photoelectric conversion efficiency. Recently, planar inverted single-junction and tandem perovskite solar cells have made rapid progress in terms of photoelectric conversion efficiency. Among them, the successful application of self-assembled monolayer materials in the hole transport layer has played a significant role in promoting the photoelectric performance of the cells (S. Liu, J. Li, W. Xiao, R. Chen, Z. Sun, Y. Zhang, X. Lei, S. Hu, M. Kober-Czerny, J. Wang, F. Ren, Q. Zhou, H. Raza, Y. Gao, Y. Ji, S. Li, H. Li, L. Qiu, W. Huang, Y. Zhao, B. Xu, Z. Liu, H. J. Snaith, N.-G. Park, W. Chen, Nature 2024, 632, 536-542.).

[0003] Self-assembled monolayer hole transport materials are anchored to a transparent metal oxide substrate through physical / chemical interactions to form an ultrathin molecular interface, which has advantages such as less material consumption and low parasitic absorption. It can effectively accelerate interfacial charge extraction, passivate surface and interface defect states, and regulate perovskite crystal growth, etc. (M. Azam, T. Du, Z. Wan, H. Zhao, H. Zeng, R. Wei, C. J. Brabec, J. Luo, C. Jia, Energy Environ. Sci. 2024, 17, 6974-7016.). Currently reported self-assembled monolayer hole transport materials generally consist of an anchoring group, a linking unit, and a bottom group with hole transport properties. The most commonly used bottom groups are rigid conjugated planar carbazoles and their derivatives, etc. For example, classic self-assembled monolayer hole transport materials such as [4-(9H-carbazol-9-yl)butyl]phosphonic acid (4PACz), [4-(3,6-dimethyl-9h-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz), etc.

[0004] To further improve the optoelectronic performance of perovskite solar cells, numerous research groups have been dedicated to the design and development of novel self-assembled monolayer hole transport materials. Professor Dewei Zhao's research group at Sichuan University prepared a self-assembled monolayer hole transport material, 4-PADCB, by introducing a benzene ring onto carbazole through a conjugated extension strategy to enhance molecular packing and hole transport characteristics, and achieved a fully perovskite tandem solar cell with a power conversion efficiency of 27% (Z. Yi, W. Wang, R. He, J. Zhu, W. Jiao, Y. Luo, Y. Xu, Y. Wang, Z. Zeng, K. Wei, J. Zhang, S.-W. Tsang, C. Chen, W. Tang, D. Zhao, Energy Environ. Sci. 2024, 17, 202-209); Professor Yi Hou's research group at the National University of Singapore prepared a self-assembled monolayer hole transport material, DCB-Br-2, by modifying 4-PADCB with heavy atom bromine, effectively adjusted the interfacial energy level alignment, promoted rapid hole extraction, and obtained a wide-bandgap perovskite solar cell with an open-circuit voltage of 1.37 V and a fully perovskite tandem solar cell with a power conversion efficiency of 27.7% (Z. Wei, Q. Zhou, X. Niu, S. Liu, Z. Dong, H. Liang, J. Chen, Z. Shi, X. Wang, Z. Jia, X. Guo, R. Guo, X. Meng, Y. Wang, N. Li, Z. Xu, Z. Li, A.G. Aberle, X. Yin, Y. Hou, Energy Environ. Sci. 2025, 18, 1847-1855.); In the same year, Professor Zhaokui Wang's research group at Soochow University prepared self-assembled monolayer hole transport materials, MeS-CbzPh and MeS-CbzPh, by using heteroatom engineering and conjugated extension strategies. Such materials exhibited excellent charge transport performance and the ability to passivate defects at the perovskite bottom interface. Finally, a single-junction perovskite solar cell based on MeS-CbzPh achieved a power conversion efficiency of 26.01% (C.-H. Chen, G.-W. Liu, X. Chen, C. Deger, R.-J. Jin, K.-L. Wang, J. Chen, Y. Xia, L. Huang, I. Yavuz, J. Fan, Z.-K. Wang, Angew. Chem. Int. Ed. 2025, 64, e202419375.). It can be seen that regulating the molecular structure of self-assembled monolayer hole transport materials through molecular engineering means is one of the effective ways to improve the performance of perovskite solar cells.

[0005] In view of the above research, the present invention selects the 9,9-dimethyl-N-phenyl-fluorene unit as the bottom group, and constructs an asymmetric self-assembled monolayer hole transport material to enhance the molecular dipole moment and strengthen the intermolecular dipole-dipole interaction, thereby suppressing non-radiative recombination inside the device, enhancing charge extraction and transport at the interface, and ultimately effectively improving the optoelectronic performance of the battery device. There are no relevant reports on such asymmetric self-assembled monolayer hole transport materials. Its successful development will be of great significance to the technological progress and commercial application of perovskite solar cells. Summary of the Invention

[0006] In order to overcome the disadvantages and deficiencies in the prior art, the object of the present invention is to develop an asymmetric self-assembled monolayer hole transport material with excellent charge transport performance, which can assist perovskite crystal growth and effectively passivate the buried interface. The present invention can not only improve the growth and crystallization environment of perovskite, enhance the crystal quality and film morphology of perovskite, but also passivate the buried defects of perovskite, improve interface contact, promote carrier transport at its surface and interface, and thus improve the optoelectronic performance and stability of perovskite solar cells.

[0007] The technical solution adopted by the present invention is as follows:

[0008] The present invention provides an asymmetric self-assembled monolayer hole transport material containing a 9,9-dimethyl-N-phenyl-fluorene unit, with the chemical name of (E)-(1-cyano-2-(4-(9,9-dimethyl-9H-fluoren-2-yl)(phenyl)amino)phenyl)vinyl)phosphonic acid, abbreviated as FNP. Its characteristic is that it uses the 9,9-dimethyl-N-phenyl-fluorene unit as the bottom group, the diphenylamine benzene group as the linking unit, and the cyanomethyl phosphoric acid as the anchoring group and passivating group; abbreviated as FNP, the material has the following chemical structural formula:

[0009]

[0010] The synthesis method of the self-assembled monolayer hole transport material FNP is as follows: p-bromobenzaldehyde and 9,9-dimethyl-N-phenyl-fluorene (Compound 1) undergo Buchwald-Hartwig coupling reaction to obtain Intermediate 2; Intermediate 2 and diethyl cyanomethylphosphonate undergo Knoevenagel condensation reaction to obtain Intermediate 3; Intermediate 3 undergoes hydrolysis reaction to obtain the final product FNP. The specific steps are as follows:

[0011] (i) Compound 1, p-bromobenzaldehyde, palladium acetate, potassium tert-butoxide, tri-tert-butylphosphine and toluene solvent were added to a dry reaction vessel to form a mixed solution, which was stirred evenly under nitrogen protection and heated to 100-120° C. for 12-24 hours. After the reaction, the reaction solution was cooled to room temperature and extracted with dichloromethane solution. The organic layer was collected and the solvent was removed under reduced pressure. The collected material was separated and purified by silica gel chromatography and dried in vacuo to obtain a light yellow solid compound 2.

[0012] (ii) Compound 2, diethyl cyanomethylphosphate, piperidine, and toluene solvent were added to a dry reaction vessel, stirred uniformly under nitrogen protection, and heated to 100-120°C for 10-15 hours. After the reaction, the reaction solution was cooled to room temperature and extracted with dichloromethane solution. The organic layer was collected, and the solvent was removed under reduced pressure. The collected material was separated and purified by silica gel chromatography and dried in vacuo to obtain an orange-red solid compound 3.

[0013] (iii) Compound 3 and dichloromethane solvent were added to a dry reaction vessel and stirred evenly in an ice-water bath under nitrogen protection. Then, trimethylsilyl bromide was slowly added dropwise and the temperature was raised to room temperature and stirred for 12-24 hours. Methanol was then added to quench the reaction and stirred at room temperature for 12-24 hours. After the reaction was completed, the solvent was removed by vacuum distillation. The collected material was recrystallized with ethanol and water and dried in vacuo to obtain an orange-red solid self-assembled monolayer hole transport material FNP.

[0014] The synthetic route is as follows:

[0015]

[0016] In step (i), the molar ratio of compound 1: p-bromobenzaldehyde: potassium tert-butoxide: palladium acetate: tri-tert-butylphosphine is 1:1.2-1.5:1.5-3:0.2-0.5:0.4-1; and the concentration of compound 1 is 0.1-0.2 mol / L.

[0017] In step (ii), the molar ratio of compound 2: diethyl cyanomethyl phosphate: piperidine is 1:2.4-3:3-4; and the concentration of compound 2 is 0.05-0.08 mol / L.

[0018] In step (iii), the molar ratio of compound 3 to trimethylsilyl bromide is 1:2-4; and the concentration of compound 3 is 0.03-0.05 mol / L.

[0019] The self-assembled monolayer hole transport material containing 9,9-dimethyl-N-phenyl-fluorene units prepared by the present invention is used as a hole transport layer in a perovskite solar cell. The perovskite solar cell is composed of a transparent conductive substrate, a hole transport layer, a perovskite light absorption layer, an electron transport layer, a hole blocking layer, and a metal electrode. The specific preparation steps are as follows:

[0020] (1) Cut the transparent conductive substrate into a fixed size and perform an etching treatment. Ultrasonically clean the etched conductive substrate in different solvents in sequence, and then perform ultraviolet ozone treatment on it;

[0021] (2) Transfer the conductive substrate treated in step (1) to a glove box, and cover the ethanol solution containing the self-assembled monolayer hole transport material FNP on the conductive substrate by spin coating or dipping method, and sinter at 100-120 °C for 5-10 minutes to prepare a self-assembled monolayer hole transport layer;

[0022] (3) Spin coat the perovskite precursor solution on the self-assembled monolayer hole transport layer, and during the spin coating of the perovskite precursor solution, dropwise add an antisolvent to form a perovskite light absorption layer;

[0023] (4) Prepare an organic electron transport layer and a hole blocking layer on the perovskite photoactive layer by spin coating or vacuum evaporation method in sequence;

[0024] (5) Deposit the metal electrode on the electron transport layer by vacuum evaporation method.

[0025] In step (1), the transparent conductive substrate is one of FTO conductive glass, ITO conductive glass, or a transparent flexible conductive substrate; the solvents are deionized water, acetone, and ethanol in sequence;

[0026] In step (2), the self-assembled monolayer hole transport material solution is prepared by dissolving 0.2-2 mg of the hole transport material in 1 mL of ethanol;

[0027] In step (3), the perovskite light absorption layer is CsxFA 1-x PbI3(0 ≤ x ≤ 1), CsxFA 1-x PbI y Br 3-y (0 ≤ x ≤ 1, 1 ≤ y ≤ 3), and the preparation method of the CsxFA 1-x PbI3(0 ≤ x ≤ 1) perovskite precursor solution is: in a glove box, mix cesium iodide, formamidinium iodide, lead iodide, and methylammonium chloride in a specific ratio and dissolve them in a mixed solution of N,N-dimethylformamide:dimethyl sulfoxide with a volume ratio of 4:1, and then stir at room temperature to obtain the perovskite precursor solution; the CsxFA 1-xPbI y Br 3-y (0≤x≤1,1≤y≤3) The preparation method of the perovskite precursor solution is as follows: In a glove box, cesium iodide, lead thiocyanate, formamidinium iodide, lead iodide and lead bromide in specific proportions are mixed and dissolved in a mixed solution of N,N-dimethylformamide:dimethyl sulfoxide with a volume ratio of 3:1, and then stirred at 60 °C to obtain the perovskite precursor solution; The anti-solvent is one or more of chlorobenzene, diethyl ether, ethyl acetate or anisole;

[0028] In step (4), the electron transport layer is one or more of fullerene derivatives (PCBM) or organic small molecule electron transport materials; The buffer layer is one or more of BCP, TiOx, PEIE or Bphen;

[0029] In step (5), the metal electrode is one of gold, silver or copper.

[0030] (2), (3), (4), and (5) The operation steps are all completed in a glove box filled with nitrogen.

[0031] The beneficial effects of the present invention are:

[0032] The asymmetric self-assembled monolayer hole transport material FNP provided by the present invention uses a 9,9-dimethyl-N-phenyl-fluorene unit as the bottom group, a diphenylamine group as the linking unit, and cyanomethylphosphonic acid as the anchoring group and passivating group; The self-assembled monolayer hole transport material FNP with an asymmetric structure can effectively improve the hole extraction and transport performance of the material, and the cyanomethylphosphonic acid in the material can effectively improve the crystallization performance of perovskite on the self-assembled monolayer, optimize the crystallization quality and film morphology of perovskite, and at the same time improve the interface contact and promote the efficient transport of carriers. This self-assembled monolayer hole transport material has the advantages of simple synthesis, low cost, excellent charge transport performance, and being adaptable to perovskites with different bandgaps. It obtains a photoelectric conversion efficiency of >23% and >19% in perovskite solar cells with a conventional bandgap of 1.52 eV and a wide bandgap of 1.77 eV respectively, and is also conducive to further reducing the commercialization cost of perovskite solar cell technology. Description of the Drawings

[0033] Figure 1 It is the chemical structural formula of the FNP material prepared by the present invention and the classic monolayer self-assembled material 4PACz;

[0034] Figure 2 (a) is the hydrogen nuclear magnetic resonance spectrum of the FNP material prepared by the present invention; (b) is the high-resolution mass spectrum of the FNP material prepared by the present invention;

[0035] Figure 3Ultraviolet photoelectron spectroscopy of the FNP self-assembled monolayer deposited on ITO prepared according to the present invention;

[0036] Figure 4 Schematic diagram of the structure of the perovskite solar cell prepared according to the present invention (1 is the ITO transparent conductive layer, 2 is the self-assembled monolayer hole transport layer, 3 is the perovskite photoactive layer with a band gap of 1.52 eV or 1.77 eV, 4 is the electron transport layer and hole blocking layer, 5 is the metal back electrode);

[0037] Figure 5 J-V curve diagram of the 1.52 eV band gap perovskite solar cell (Examples 1 and Comparative Example 1) based on the FNP material and 4PACz material of the present invention (light intensity is 100 mW / cm 2 );

[0038] Figure 6 J-V curve diagram of the 1.77 eV band gap perovskite solar cell (Examples 2 and Comparative Example 2) based on the FNP material and 4PACz material of the present invention (light intensity is 100 mW / cm 2 );

[0039] Figure 7 IPCE diagram of the 1.52 eV band gap perovskite solar cell (Examples 1 and Comparative Example 1) based on the FNP material and 4PACz material of the present invention;

[0040] Figure 8 IPCE diagram of the 1.77 eV band gap perovskite solar cell (Examples 2 and Comparative Example 2) based on the FNP material and 4PACz material of the present invention. Detailed implementation manners

[0041] The following further illustrates the present invention with specific implementation examples to enable those skilled in the art to 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.

[0042] Example 1:

[0043] Synthesis of the self-assembled monolayer hole transport material FNP containing 9,9-dimethyl-N-phenyl-fluorene unit and its application in the 1.52 eV band gap perovskite solar cell:

[0044] [[ID=XXX]] [[ID=XXX]]

[0045] (i) Compound 1 (1.00 g, 3.50 mmol), p-bromobenzaldehyde (0.78 g, 4.22 mmol), palladium acetate (0.16 g, 0.71 mmol), potassium tert-butoxide (1.19 g, 10.50 mmol), tri-tert-butylphosphine (0.28 g, 1.43 mmol) and toluene (20 mL) were added to a dry reaction vessel. The mixture was stirred evenly under nitrogen protection and heated to 120°C for 24 h. After the reaction, the reaction solution was cooled to room temperature and extracted with dichloromethane solution (150 mL) three times. The organic layer was collected and the solvent was removed under reduced pressure. The collected material was separated and extracted using a silica gel chromatography column with petroleum ether / dichloromethane (1:1 vol / vol) as the eluent. The mixture was dried in vacuo to obtain compound 2 (1.02 g, yield: 74.7%) as a pale yellow solid. 1 H NMR(400MHz, CDCl3-d)δ9.91–9.85(m,1H),7.79–7.69(m,4H),7.47(d,J=7.1Hz, 1H),7.44–7.33(m,4H),7.33–7.23(m,4H),7.19–7.10(m,3H),1.51–1.46(m,6H).

[0046] (ii) Compound 2 (0.49 g, 1.26 mmol), diethyl cyanomethylphosphonate (0.54 g, 3.05 mmol), piperidine (0.42 g, 4.93 mmol) and toluene (20 mL) were added to a dry reaction vessel and stirred evenly under nitrogen protection. The mixture was heated to 100°C for 10 h. After the reaction, the reaction solution was cooled to room temperature and extracted with dichloromethane solution (150 mL). The organic layer was collected and the solvent was removed under reduced pressure. The collected material was separated and purified by silica gel chromatography and dried in vacuo with dichloromethane / methanol (10:1 vol / vol) to obtain an orange-red solid compound 3 (0.48 g, yield: 69.5%). 1 HNMR (400 MHz, CDCl3-d) δ 7.90–7.79 (m, 3H), 7.72–7.63 (m, 2H), 7.42 (dd, J = 7.3, 1.4 Hz, 1H), 7.39–7.28 (m, 4H), 7.26–7.16 (m, 4H), 7.11 (dd, J = 8.1, 2.0 Hz, 1H), 7.07–7.00 (m, 2H), 4.20 (dqd, J = 8.3, 7.1, 5.2 Hz, 4H), 1.40 (t, J = 7.1 Hz, 6H). HRMS: calculated: C 34 H 33 N2O3P 549.2229, measured: 549.2292.

[0047] (iii) Add compound 3 (0.20 g, 0.36 mmol) and the solvent dichloromethane (10 mL) into a dry reaction vessel. Stir evenly under an ice-water bath and nitrogen protection. Then slowly dropwise add trimethylsilyl bromide (0.22 g, 1.44 mmol) and warm up to room temperature and stir for 12 h. After that, add methanol (2 mL) to quench the reaction and stir at room temperature for 12 h. After the reaction is completed, remove the solvent by distillation under reduced pressure. The collected product is recrystallized with ethanol and water and dried in vacuo to obtain the orange-red solid self-assembled monolayer hole transport material FNP (0.16 g, yield: 89.1%). 1 H NMR (400 MHz, DMSO-d6) δ 7.94–7.46 (m, 5H), 7.40–7.11 (m, 8H), 7.08–6.82 (m, 4H), 1.34 (d, J = 17.9 Hz, 6H). HRMS: Calculated value: C 30 H 25 N2O3P491.1603, found: 491.1523.

[0048] The above-synthesized self-assembled monolayer hole transport material FNP is applied to a perovskite solar cell with a band gap of 1.52 eV. Its preparation method and process are as follows:

[0049] The cell structure of the perovskite solar cell is ITO / FNP / Perovskite(1.52 eV) / C 60 / BCP / Ag. The preparation process of the perovskite solar cell with a band gap of 1.52 eV is as follows:

[0050] (1) Cut the ITO (indium tin oxide) conductive glass into a glass substrate with a size of 15 mm × 15 mm, and etch it using an etching machine. Ultrasonically clean the etched glass substrate in deionized water, acetone, and ethanol for 30 min in sequence, and then place it in an ultraviolet ozone machine for treatment for 30 min.

[0051] (2) Prepare the organic self-assembled monolayer hole transport layer by spin coating. First, dissolve 0.5 mg of FNP in 1 mL of ethanol, and then shake it well to mix evenly to obtain the precursor solution of the self-assembled monolayer hole transport layer. Finally, use a pipette to suck 30 μL of the solution and coat it on the ITO conductive substrate, control the rotation speed to 3000 rpm, and the spin coating time to 30 s. Then anneal the self-assembled monolayer hole transport layer film at 100 °C for 10 min to obtain a dense and uniform FNP self-assembled monolayer hole transport layer film.

[0052] (3) The perovskite photoactive layer with a bandgap of 1.52 eV was prepared by spin coating. In a glove box, cesium iodide (19.5 mg, 0.075 mmol), formamidinium iodide (245.1 mg, 1.425 mmol), lead iodide (705.3 mg, 1.53 mmol), and methylammonium chloride (10.1 mg, 0.15 mmol) were dissolved in 1 mL of a mixed solution of N,N-dimethylformamide:dimethyl sulfoxide with a volume ratio of 4:1, and then stirred at room temperature to obtain a perovskite precursor solution with a bandgap of 1.52 eV. Using a spin coater, 50 μL of the prepared perovskite precursor solution with a bandgap of 1.52 eV was spin-coated on the FNP self-assembled monolayer hole transport layer film, controlling the rotation speed to be 4000 rpm and the spin coating time to be 50 s, and 100 μL of chlorobenzene was dropped onto the film 20 seconds before the end. Then, the perovskite film was annealed at 100 °C for 30 min to obtain a dense and uniform perovskite film with a bandgap of 1.52 eV.

[0053] (4) The electron transport layer and hole blocking layer were prepared by vacuum evaporation. High-purity C 60 and BCP were successively and uniformly deposited onto the perovskite film at rates of about 0.2 and respectively, and the evaporation thicknesses were 25 and 8 nm respectively.

[0054] (5) The counter electrode was prepared by vacuum evaporation. High-purity silver was uniformly deposited onto the device film at a rate of or so, and the evaporation thickness was 100 nm. In addition, the evaporation area of gold was 20 mm 2 through a specific mold.

[0055] Example 2:

[0056] Synthesis of a self-assembled monolayer hole transport material FNP containing 9,9-dimethyl-N-phenyl-fluorene units and its application in perovskite solar cells with a bandgap of 1.77 eV:

[0057]

[0058] (i) Compound 1 (0.80 g, 2.80 mmol), p-bromobenzaldehyde (0.62 g, 3.37 mmol), palladium acetate (0.13 g, 0.56 mmol), potassium tert-butoxide (0.63 g, 5.61 mmol), tri-tert-butylphosphine (0.24 g, 1.19 mmol) and toluene (20 mL) were added to a dry reaction vessel. The mixture was stirred evenly under nitrogen and heated to 120°C for 24 h. After the reaction, the reaction solution was cooled to room temperature and extracted with dichloromethane solution (150 mL) three times. The organic layer was collected and the solvent was removed under reduced pressure. The collected material was separated and extracted using a silica gel chromatography column with petroleum ether / dichloromethane (1:1 vol / vol) as the eluent. The mixture was dried in vacuo to obtain compound 2 (0.58 g, yield: 53.1%) as a pale yellow solid. 1 H NMR(400MHz, CDCl3-d)δ9.91–9.85(m,1H),7.79–7.69(m,4H),7.47(d,J=7.1Hz, 1H),7.44–7.33(m,4H),7.33–7.23(m,4H),7.19–7.10(m,3H),1.51–1.46(m,6H).

[0059] (ii) Compound 2 (0.49 g, 1.26 mmol), diethyl cyanomethylphosphate (0.65 g, 3.67 mmol), piperidine (0.39 g, 4.58 mmol) and toluene (20 mL) were added to a dry reaction vessel. The mixture was stirred evenly under nitrogen protection and heated to 100°C for 10 h. After the reaction, the reaction solution was cooled to room temperature and extracted with dichloromethane solution (150 mL). The organic layer was collected and the solvent was removed under reduced pressure. The collected material was separated and purified by silica gel chromatography and dried in vacuo with dichloromethane / methanol (10:1 vol / vol) to obtain an orange-red solid compound 3 (0.40 g, yield: 57.91%). 1 HNMR (400 MHz, CDCl3-d) δ 7.90–7.79 (m, 3H), 7.72–7.63 (m, 2H), 7.42 (dd, J = 7.3, 1.4 Hz, 1H), 7.39–7.28 (m, 4H), 7.26–7.16 (m, 4H), 7.11 (dd, J = 8.1, 2.0 Hz, 1H), 7.07–7.00 (m, 2H), 4.20 (dqd, J = 8.3, 7.1, 5.2 Hz, 4H), 1.40 (t, J = 7.1 Hz, 6H). HRMS: calculated: C 34 H 33 N2O3P 549.2229, measured: 549.2292.

[0060] (iii) Add compound 3 (0.25 g, 0.46 mmol) and the solvent dichloromethane (10 mL) to a dry reaction vessel. Stir evenly under an ice-water bath and nitrogen protection, then slowly add trimethylsilyl bromide (0.14 g, 0.92 mmol) and warm up to room temperature and stir for 16 h. Then add methanol (2 mL) to quench the reaction and stir at room temperature for 16 h. After the reaction is completed, remove the solvent by distillation under reduced pressure. The collected product is recrystallized with ethanol and water and dried in vacuo to obtain the orange-red solid self-assembled monolayer hole transport material FNP (0.18 g, yield: 80.2%). 1 H NMR (400 MHz, DMSO-d6) δ 7.94–7.46 (m, 5H), 7.40–7.11 (m, 8H), 7.08–6.82 (m, 4H), 1.34 (d, J = 17.9 Hz, 6H). HRMS: calculated value: C 30 H 25 N2O3P491.1603, found value: 491.1523.

[0061] The above-synthesized self-assembled monolayer hole transport material FNP is applied to a perovskite solar cell with a band gap of 1.77 eV. Its preparation method and process are as follows:

[0062] The cell structure of the perovskite solar cell is ITO / FNP / Perovskite (1.77 eV) / C 60 / BCP / Ag. The preparation process of the perovskite solar cell with a band gap of 1.77 eV is as follows:

[0063] (1) Cut the ITO (indium tin oxide) conductive glass into glass substrates with a size of 15 mm × 15 mm, and etch them using an etching machine. Ultrasonically clean the etched glass substrates in deionized water, acetone, and ethanol for 30 min in sequence, and then place them in an ultraviolet ozone machine for treatment for 30 min.

[0064] (2) Prepare the organic self-assembled monolayer hole transport layer by spin coating. First, dissolve 0.5 mg of FNP in 1 mL of ethanol, and then shake it well to mix evenly to obtain the precursor solution of the self-assembled monolayer hole transport layer. Finally, use a pipette to suck 30 μL of the solution and coat it on the ITO conductive substrate, control the rotation speed at 3000 rpm, and the spin coating time at 30 s. Then anneal the self-assembled monolayer hole transport layer film at 100 °C for 10 min to obtain a dense and uniform FNP self-assembled monolayer hole transport layer film.

[0065] (3) Prepare a perovskite photoactive layer with a bandgap of 1.77 eV using the spin-coating method. In a glove box, dissolve cesium iodide (62.4 mg, 0.24 mmol), formamidinium iodide (165.1 mg, 0.96 mmol), lead iodide (221.3 mg, 0.48 mmol), lead thiocyanate (3.88 mg, 0.012 mmol), and lead bromide (264.2 mg, 0.72 mmol) in 1 mL of a mixed solution of N,N-dimethylformamide:dimethyl sulfoxide with a volume ratio of 3:1. Then stir at 60 °C to obtain a perovskite precursor solution with a bandgap of 1.77 eV. Using a spin coater, spin coat 50 μL of the prepared perovskite precursor solution with a bandgap of 1.77 eV onto the FNP self-assembled monolayer hole transport layer film, control the rotation speed to 500 rpm, and the spin-coating time to 2 s. Subsequently, control the rotation speed to 4000 rpm and the spin-coating time to 60 s, and add 700 μL of diethyl ether to the film 25 seconds before the end. Then anneal the perovskite film at 60 °C for 2 min and then at 100 °C for 10 min to obtain a dense and uniform perovskite film with a bandgap of 1.77 eV.

[0066] (4) Prepare the electron transport layer and hole blocking layer using the vacuum evaporation method. Select high-purity C 60 and BCP are successively and uniformly deposited onto the perovskite film at rates of 0.2 and respectively, and the evaporation thicknesses are 25 and 8 nm.

[0067] (5) Prepare the counter electrode using the vacuum evaporation method. Select high-purity copper and deposit it uniformly onto the device film at a rate of respectively, and the evaporation thickness is 100 nm. In addition, make the evaporation area of gold 20 mm 2 through a specific mold.

[0068] Comparative Example 1:

[0069] Select the classic organic self-assembled monolayer hole transport material 4PACz as the hole transport layer and apply it to a perovskite solar cell with a bandgap of 1.52 eV. The preparation method and process are as follows:

[0070] The cell structure of the perovskite solar cell is ITO / 4PACz / Perovskite(1.52 eV) / C 60 / BCP / Ag. The preparation process of the perovskite solar cell with a bandgap of 1.52 eV is as follows:

[0071] (1) Cut the ITO (indium tin oxide) conductive glass into glass substrates of 15 mm × 15 mm in size, and etch them using an etching machine. Ultrasonically clean the etched glass substrates in deionized water, acetone, and ethanol for 30 min in sequence, and then place them in an ultraviolet ozone machine for 30 min.

[0072] (2) Prepare an organic self-assembled monolayer hole transport layer using the spin-coating method. First, dissolve 0.5 mg of 4PACz in 1 mL of ethanol, and then shake it thoroughly to mix evenly to obtain a precursor solution of the self-assembled monolayer hole transport layer. Finally, use a pipette to aspirate 30 μL of the solution and coat it on the ITO conductive substrate, control the rotation speed to 3000 rpm, and the spin-coating time to 30 s. Then anneal the self-assembled monolayer hole transport layer film at 100 °C for 10 min to obtain a dense and uniform FNP self-assembled monolayer hole transport layer film.

[0073] (3) Prepare a perovskite photoactive layer with a 1.52 eV bandgap using the spin-coating method. In a glove box, dissolve cesium iodide (19.5 mg, 0.075 mmol), formamidinium iodide (245.1 mg, 1.425 mmol), lead iodide (705.3 mg, 1.53 mmol), and methylammonium chloride (10.1 mg, 0.15 mmol) in 1 mL of a mixed solution of N,N-dimethylformamide:dimethyl sulfoxide with a volume ratio of 4:1, and then stir at room temperature to obtain a perovskite precursor solution with a 1.52 eV bandgap. Using a spin coater, spin-coat 50 μL of the prepared perovskite precursor solution with a 1.52 eV bandgap on the FNP self-assembled monolayer hole transport layer film, control the rotation speed to 4000 rpm, and the spin-coating time to 50 s, and add 100 μL of chlorobenzene to the film 20 seconds before the end. Then anneal the perovskite film at 100 °C for 30 min to obtain a dense and uniform perovskite film with a 1.52 eV bandgap.

[0074] (4) Prepare an electron transport layer and a hole blocking layer using the vacuum evaporation method. Select high-purity C 60 and BCP are successively and uniformly deposited on the perovskite film at rates of 0.2 and respectively, and the evaporation thicknesses are 25 and 8 nm.

[0075] (5) Prepare a counter electrode using the vacuum evaporation method. Select high-purity silver and deposit it uniformly on the device film at a rate of or so, and the evaporation thickness is 100 nm. In addition, make the evaporation area of gold 20 mm 2 through a specific mold.

[0076] Comparative Example 2:

[0077] The classic organic self-assembled monolayer hole transport material 4PACz is selected as the hole transport layer and applied to a perovskite solar cell with a 1.77 eV bandgap. The preparation method and process are as follows:

[0078] The cell structure of the perovskite solar cell is ITO / 4PACz / Perovskite(1.77eV) / C 60 / BCP / Ag. The preparation process of the 1.77 eV bandgap perovskite solar cell is as follows:

[0079] (1) Cut the ITO (indium tin oxide) conductive glass into glass substrates with a size of 15 mm × 15 mm, and etch them using an etching machine. Ultrasonically clean the etched glass substrates in deionized water, acetone, and ethanol for 30 min in sequence, and then place them in an ultraviolet ozone machine for 30 min.

[0080] (2) Prepare the organic self-assembled monolayer hole transport layer by spin coating. First, dissolve 0.5 mg of 4PACz in 1 mL of ethanol, and then shake it well to mix evenly to obtain the self-assembled monolayer hole transport layer precursor solution. Finally, use a pipette to suck 30 μL of the solution and coat it on the ITO conductive substrate, control the rotation speed at 3000 rpm, and the spin coating time at 30 s. Then anneal the self-assembled monolayer hole transport layer film at 100 °C for 10 min to obtain a dense and uniform FNP self-assembled monolayer hole transport layer film.

[0081] (3) Prepare the 1.77 eV bandgap perovskite photoactive layer by spin coating. In a glove box, dissolve cesium iodide (62.4 mg, 0.24 mmol), formamidinium iodide (165.1 mg, 0.96 mmol), lead iodide (221.3 mg, 0.48 mmol), lead thiocyanate (3.88 mg, 0.012 mmol), and lead bromide (264.2 mg, 0.72 mmol) in 1 mL of a mixed solution of N,N-dimethylformamide:dimethyl sulfoxide with a volume ratio of 3:1, and then stir at 60 °C to obtain the 1.77 eV bandgap perovskite precursor solution. Using a spin coater, spin coat 50 μL of the prepared 1.77 eV bandgap perovskite precursor solution on the FNP self-assembled monolayer hole transport layer film, control the rotation speed at 500 rpm, and the spin coating time at 2 s. Subsequently, control the rotation speed at 4000 rpm, and the spin coating time at 60 s, and add 700 μL of ether to the film 25 seconds before the end. Then anneal the perovskite film at 60 °C for 2 min and then at 100 °C for 10 min to obtain a dense and uniform 1.77 eV bandgap perovskite film.

[0082] (4) Prepare the electron transport layer and hole blocking layer by vacuum evaporation. Select high-purity C60 and BCP were successively and uniformly deposited onto the perovskite thin film at rates of 0.2 and or so, respectively, with evaporation thicknesses of 25 and 8 nm.

[0083] (5) The counter electrode was prepared by vacuum evaporation. High-purity copper was selected and uniformly deposited onto the device film at a rate of 2 or so, with an evaporation thickness of 100 nm. In addition, through a specific mold, the evaporation area of gold was 20 mm

[0084] Figure 1 The chemical structural formulas of the FNP material prepared in this invention and the classical self-assembled monolayer material 4PACz.

[0085] Figure 2 (a) The hydrogen nuclear magnetic resonance spectrum of the FNP material prepared in this invention; (b) The high-resolution mass spectrum of the FNP material prepared in this invention; It can be seen from the figure that the self-assembled monolayer hole transport material FNP was successfully prepared.

[0086] Figure 3 The ultraviolet photoelectron energy spectrum of the FNP self-assembled monolayer deposited on ITO prepared in this invention; It can be seen from the figure that after being modified with the self-assembled monolayer hole transport material FNP, the ITO has a suitable work function (-5.14 eV) and HOMO energy level (-5.68 eV), and can effectively extract and transport charges.

[0087] Figure 4 The structural schematic diagram of the perovskite solar cell prepared in this invention (1 is the ITO transparent conductive layer, 2 is the self-assembled monolayer hole transport layer, 3 is the perovskite photoactive layer with a bandgap of 1.52 eV or 1.77 eV, 4 is the electron transport layer and hole blocking layer, 5 is the metal back electrode);

[0088] Figure 5 The J-V curve diagrams of the 1.52 eV bandgap perovskite solar cells (Example 1 and Comparative Example 1) based on the FNP material and 4PACz material in this invention (the light intensity is 100 mW / cm 2 ); It can be seen from the figure that the 1.52 eV bandgap perovskite solar cells based on Example 1 and Comparative Example 1 obtained photoelectric conversion efficiencies of 23.05% (open circuit voltage Voc is 1.148 V, short circuit current density Jsc is 25.30 mA·cm -2 , fill factor FF is 79.35%) and 20.94% (open circuit voltage Voc is 1.108 V, short circuit current density Jsc is 24.21 mA·cm -2 , fill factor FF is 78.06%), respectively.

[0089] Figure 6 J-V curve diagram of 1.77 eV bandgap perovskite solar cells (Example 2 and Comparative Example 2) based on the FNP material and 4PACz material of the present invention (light intensity is 100 mW / cm 2 ); It can be seen from the figure that the 1.77 eV bandgap perovskite solar cells based on Example 2 and Comparative Example 2 obtained photoelectric conversion efficiencies of 19.84% (open-circuit voltage V oc is 1.293 V, short-circuit current density J sc is 18.44 mA·cm -2 , fill factor FF is 83.22%) and 18.20% (open-circuit voltage V oc is 1.276 V, short-circuit current density J sc is 17.96 mA·cm -2 , fill factor FF is 79.41%) respectively.

[0090] Figure 7 IPCE diagram of 1.52 eV bandgap perovskite solar cells (Example 1 and Comparative Example 1) based on the FNP material and 4PACz material of the present invention; It can be seen from the figure that the perovskite solar cell prepared based on Example 1 has higher photoelectric conversion ability at 350 nm - 800 nm, and the integrated current density of its IPCE is 24.95 mA·cm -2 (the integrated current density of the IPCE of Comparative Example 1 is 24.15 mA·cm -2 ).

[0091] Figure 8 IPCE diagram of 1.77 eV bandgap perovskite solar cells (Example 2 and Comparative Example 2) based on the FNP material and 4PACz material of the present invention. It can be seen from the figure that the perovskite solar cell prepared based on Example 2 has higher photoelectric conversion ability at 350 nm - 700 nm, and the integrated current density of its IPCE is 18.31 mA·cm -2 (the integrated current density of the IPCE of Comparative Example 2 is 17.88 mA·cm -2 ).

Claims

1. An asymmetric self-assembled monolayer material, characterized in that, It uses 9,9-dimethyl-N-phenyl-fluorene unit as the bottom group, diphenylamine phenyl group as the connecting unit, and cyanomethylphosphonic acid as the anchor group and passivation group; it is abbreviated as FNP, and its chemical structure is as follows:

2. The preparation method of the asymmetric self-assembled monolayer material according to claim 1, characterized in that, The steps are: (1) p-Bromobenzaldehyde and 9,9-dimethyl-N-phenyl-fluorene undergo Buchwald-Hartwig coupling reaction to obtain intermediate 2; (2) Intermediate 2 reacts with diethyl cyanomethylphosphate to produce intermediate 3 through Knoevenagel condensation reaction; (3) Intermediate 3 is hydrolyzed to obtain the final product FNP.

3. The preparation method of the asymmetric self-assembled monolayer material according to claim 2, wherein, The specific steps are: (i) 9,9-dimethyl-N-phenyl-fluorene, p-bromobenzaldehyde, palladium acetate, potassium tert-butoxide, tri-tert-butylphosphine and solvent toluene were added to a dry reaction vessel to form a mixed solution, which was stirred evenly under nitrogen protection and heated to react. After the reaction was completed, the reaction solution was cooled to room temperature and extracted with dichloromethane solution. The organic layer was collected, the solvent was removed under reduced pressure, and the collected material was separated and purified by silica gel chromatography and dried in vacuo to obtain a light yellow solid compound 2; (ii) Compound 2, diethyl cyanomethylphosphate, piperidine, and toluene solvent were added to a dry reaction vessel, stirred uniformly under nitrogen protection, and heated to react. After the reaction was completed, the reaction solution was cooled to room temperature and extracted with dichloromethane solution. The organic layer was collected, the solvent was removed under reduced pressure, and the collected material was separated and purified by silica gel chromatography and dried in vacuo to obtain an orange-red solid compound 3; (iii) Compound 3 and dichloromethane solvent were added to a dry reaction vessel and stirred uniformly in an ice-water bath under nitrogen protection. Then, trimethylsilyl bromide was slowly added dropwise and the temperature was raised to room temperature and stirred for a first period of time. After that, methanol was added to quench the reaction and stirred at room temperature for a second period of time. After the reaction was completed, the solvent was removed by vacuum distillation. The collected material was recrystallized with ethanol and water and dried in vacuo to obtain an orange-red solid self-assembled monolayer hole transport material FNP.

4. The preparation method of the asymmetric self-assembled monolayer material according to claim 3, characterized in that, In step (i), the molar ratio of 9,9-dimethyl-N-phenyl-fluorene: p-bromobenzaldehyde: potassium tert-butoxide: palladium acetate: tri-tert-butylphosphine is 1:1.2-1.5:1.5-3:0.2-0.5:0.4-1; and the concentration of compound 1 is 0.1-0.2 mol / L.

5. The preparation method of the asymmetric self-assembled monolayer material according to claim 3, characterized in that, In step (i), the heating reaction temperature is 100-120° C., and the reaction time is 12-24 h.

6. The preparation method of the asymmetric self-assembled monolayer material according to claim 3, characterized in that, In step (ii), the molar ratio of compound 2: diethyl cyanomethyl phosphate: piperidine is 1:2.4-3:3-4; and the concentration of compound 2 is 0.05-0.08 mol / L.

7. The preparation method of the asymmetric self-assembled monolayer material according to claim 3, characterized in that In step (ii), the heating reaction temperature is 100-120° C., and the reaction time is 10-15 h.

8. The method for preparing the asymmetric self-assembled monolayer material according to claim 3, characterized in that, In step (iii), the molar ratio of compound 3 to trimethylsilyl bromide is 1:2-4; and the concentration of compound 3 is 0.03-0.05 mol / L.

9. The preparation method of the asymmetric self-assembled monolayer material according to claim 3, wherein In step (iii), the first stirring period is 12-24 h at room temperature, and the second stirring period is 12-24 h at room temperature.

10. The asymmetric self-assembled monolayer material described in claim 1 is applied as a hole transport layer in a perovskite solar cell.

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