Organic small molecule photovoltaic material based on benzopyrazine donor core and preparation method and application thereof

Abstract

The invention provides an organic small molecule photovoltaic material based on a benzopyrazine donor core and a preparation method and application thereof. The small organic molecule photovoltaic material based on the benzopyrazine donor core is synthesized by taking a core for expanding the conjugation degree of a traditional receptor small molecule Y6 intermediate skeleton as an intermediate donor unit; the small organic molecule photovoltaic material has good processability, and has good dissolving capacity in common organic solvents; meanwhile, the soluble small organic molecule photovoltaic materials are well accumulated on the film, and the absorption of the film has obvious red shift relative to the solution; when the small organic molecule photovoltaic material based on the benzopyrazine donor core provided by the invention is used as an acceptor material and is blended with a polymer donor material D18, the energy conversion efficiency exceeds 18%, the open-circuit voltage exceeds 0.94 eV, and the energy loss is reduced to 0.502 eV.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic materials technology, specifically relating to an organic small molecule photovoltaic material based on benzopyrazine donor cores, its preparation method, and its application. Background Technology

[0002] In recent years, organic solar cells have attracted widespread attention due to their advantages such as being able to be processed in solution, low cost, light weight, semi-transparency, and ease of fabrication of large-area flexible thin-film devices ((a) S. Gunes, H. Neugebauer, NSSariciftci, Conjugated Polymer-Based Organic Solar Cells) Chemical Reviews 2007, 107 , 1324-1338. (b) G. Li, V. Shrotriya, JS Huang, Y. Yao, T.Moriarty, K. Emery, Y. Yang, High-efficiency solution processable polymerphotovoltaic cells by self-organization of polymer blends Nature Materials 2005, 4 , 864-868. (c) JH Hou, O. Inganas, RH Friend, F. Gao, Organicsolar cells based on non-fullerene acceptors Nature Materials 2018, 17 , 119-128.).

[0003] Non-fullerene acceptor materials exhibit significant advantages in light absorption properties, donor compatibility, and electroluminescence properties. With the rapid development of material structure and device technology, the optimal photoelectric conversion efficiency of organic solar cells based on non-fullerene acceptor materials has reached 19% ((a) C. Li, JD Zhou, JL Song, JQ Xu, HTZhang, XN Zhang, J. Guo, L. Zhu, DH Wei, GC Han, J. Min, Y. Zhang, ZQ Xie, YP Yi, H. Yan, F. Gao, F. Liu, YM Sun, Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells). Nat. Energy 2021, 6 , 605-613. (b) L.Meng, Y. Zhang, X. Wan, C. Li, X. Zhang, Y. Wang, X. Ke, Z. Xiao, L. Ding, R.Xia, HL Yip, Y. Cao, Y. Chen, Organic and solution-processed tandem solar cells with 17.3% efficiency Science 2018, 361 , 1094-1098. (c) Y. Cui, Y. Xu,HF Yao, PQ Bi, L. Hong, JQ Zhang, YF Zu, T. Zhang, JZ Qin, JZ Ren, ZH Chen, C. He, XT Hao, ZX Wei, JH Hou, Single-JunctionOrganic Photovoltaic Cell with 19% Efficiency Adv. Mater. 2021, 33 ,2102420.).

[0004] However, the photoelectric conversion efficiency of organic solar cells is still lower than that of crystalline silicon solar cells and perovskite solar cells ((a) K. Yoshikawa, H. Kawasaki, W. Yoshida, T. Irie, K. Konishi, K. Nakano, T. Uto, D. Adachi, M. Kanematsu, H. Uzu, K. Yamamoto, Siliconheterojunction solar cell with interdigitated back contacts for aphotoconversion efficiency over 26%) Nat. Energy 2017, 2 , 17032. (b) Z. Liu,L. Krückemeier, B. Krogmeier, B. Klingebiel, JA Márquez, S. Levcenko, S. Öz, S. Mathur, U. Rau, T. Unold, T. Kirchartz, Significant Advances in EnergyResearch ACS Energy Lett. 2018, 4 , 110-117. (c) JZ Yao, T. Kirchartz, MS Vezie, MA Faist, W. Gong, ZC He, HB Wu, J. Troughton, T. Watson,D. Bryant, J. Nelson, Optimal State Choice for Rydberg-Atom Microwave Sensors Phys. Rev. Appl. 2015, 4 , 014020.).

[0005] In fact, the open-circuit voltage of most high-performance organic solar cells is still limited to 0.8-0.9 V. Exciton dissociation and recombination processes require additional energy, and significant energy loss is a major factor limiting the photoelectric conversion efficiency of organic solar cells. ((a) L. Hong, H. Yao, Z. Wu, Y. Cui, T. Zhang, Y. Xu, R. Yu, Q. Liao, B. Gao, K. Xian, HY Woo, Z. Ge, J. Hou, Regulating Bulk-HeterojunctionMolecular Orientations through Surface Free Energy Control of Hole-Transporting Layers for High-Performance Organic Solar Cells) Adv. Mater. 2019, 31 , e1903441. (b) S. Liu, J. Yuan, W. Deng, M. Luo, Y. Xie, Q. Liang, Y. Zou, Z. He, H. Wu, Y. Cao, High-efficiency organic solar cells with lownon-radiative recombination loss and low energetic disorder Nature Photon. 2020, 14 (300-305). Therefore, further reducing the losses of organic solar cells remains challenging. To effectively improve the performance and reduce the losses of organic solar cells, it is also necessary to optimize the structure of non-fullerene acceptor materials.

[0006] Benzopyrazines and their derivatives possess significant advantages such as weak electron-deficient properties, rigid planar structures, ease of chemical modification, and multiple substitution positions, thereby allowing for fine-tuning of their physicochemical properties. ((a) CK Sun, C. Zhu, L. Meng, YFLi, A Quinoxaline-Based D–A Copolymer Donor Achieving 17.62% Efficiency of Organic Solar Cells) Adv. Mater.2021, 2104161. (b) ZY Zhang, Q. Peng, DB Yang, YQ Chen, Y. Huang, XM Pu, ZY Lu, Q. Jiang, Y. Liu, Novelconjugated polymers with planar backbone bearing acenaphtho[1,2-b]quinoxalineacceptor subunit for polymer solar cells Synth. Met. 2013, 175 (21-29). Therefore, benzopyrazine and its derivatives are widely used in polymer donor materials and non-fullerene acceptor materials.

[0007] In the fabrication of large-area devices using benzopyrazine and its derivative Qx-2 via slot coating, the excessive crystallinity of Qx-2 leads to early phase separation and aggregation. This overcrystallization inhibits material uniformity, resulting in the formation of large crystal domains and affecting the efficient transport of electrons and holes. (Y.-F. Shen, H. Zhang, J. Zhang, C. Tian, ​​Y. Shi, D. Qiu, Z. Zhang, K. Lu, Z. Wei, In Situ Absorption Characterization Guided Slot-Die-Coated High-Performance Large-Area Flexible Organic SolarCells and Modules Adv Mater 2023, 35, 2209030.). Ultimately, this results in poor photovoltaic performance, with a power conversion efficiency (PCE) below 1%.

[0008] How to apply benzopyrazine donor units, which have good planarity and are easy to chemically modify, to solution-processable small acceptor molecules to prepare solution-processable organic small acceptor molecules with good planarity, good crystallinity, and high efficiency has become an urgent problem to be solved. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide an organic small-molecule photovoltaic material based on a benzopyrazine donor core, its preparation method, and its applications. This invention uses a core that expands the conjugation degree of the traditional acceptor small molecule Y6 as the intermediate electron-donating unit. Trifluorophenyl groups are introduced into the central core through conjugation extension, and the number of substituted trifluorobenzenes is controlled to precisely regulate the material's crystallinity, large-area processability, and stability. Electron-withdrawing units such as dicyandiamide are symmetrically connected at both ends. The organic small-molecule photovoltaic material designed and synthesized by this invention exhibits good molecular stacking, well-matched energy levels, suitable crystallinity, and suitability for large-area solution processing. When used in organic solar cells, it can improve their energy conversion efficiency.

[0010] To achieve this objective, the present invention adopts the following technical solution: On one hand, the present invention provides an organic small molecule photovoltaic material based on a benzopyrazine donor core, wherein the organic small molecule photovoltaic material has the following structure: Where D is the donor unit and A is the acceptor unit; The donor unit is selected from any one of the structures shown in Equation I-1 or Equation I-2, wherein Indicates the receptor unit connection location: ; Wherein, R1 is selected from any one of alkyl, acetal or aromatic alkyl; R2 is selected from alkyl or silyl; R3 and R4 are each independently selected from any one of hydrogen, halogen, alkyl, substituted or unsubstituted thiophene, substituted or unsubstituted benzene ring, wherein the number of carbon atoms of the above alkyl, acetal or silyl groups is 5-20 (e.g. 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 or 20, etc.); X1-X3 are each independently selected from sulfur or selenium atoms.

[0011] This invention applies intermediate donor and acceptor units with good planarity and ease of chemical modification to the design and synthesis of soluble organic small molecule photovoltaic materials; it prepares solutions with good planarity, good crystallinity, and high efficiency for processing organic acceptor small molecules; these soluble organic small molecule photovoltaic materials exhibit good packing on the membrane, and the membrane absorption shows a significant red shift relative to the solution; moreover, the organic small molecule photovoltaic materials based on benzopyrazine donor cores synthesized in this invention, as acceptor materials, have the advantage of matching HOMO and LUMO energy levels with the donor materials; and these organic small molecule acceptor materials do not exhibit batch-to-batch variation and have good reproducibility; when the organic small molecule photovoltaic materials based on benzopyrazine donor cores provided in this invention are blended with polymer donor material D18, the energy conversion efficiency exceeds 18%, the open-circuit voltage exceeds 0.94 eV, and the energy loss is reduced to 0.502 eV.

[0012] In this invention, the donor unit shown is selected from any of the following structures: .

[0013] The organic small molecule photovoltaic materials based on benzopyrazine donor cores provided by this invention have a defined molecular weight compared to polymer materials, do not have molecular weight distribution issues, and have a smaller impact on material quality from different synthesis batches.

[0014] In this invention, R1 is selected from any one of C6-C11 straight-chain alkyl groups (e.g., C6 straight-chain alkyl, C7 straight-chain alkyl, C8 straight-chain alkyl, C9 straight-chain alkyl, C10 straight-chain alkyl, C11 straight-chain alkyl, etc.), C6-C11 branched-chain alkyl groups (e.g., C6 branched-chain alkyl, C7 branched-chain alkyl, C8 branched-chain alkyl, C9 branched-chain alkyl, C10 branched-chain alkyl, C11 branched-chain alkyl, etc.), C6-C11 alcohol groups (e.g., C6 alcohol group, C7 alcohol group, C8 alcohol group, C9 alcohol group, C10 alcohol group, C11 alcohol group, etc.), or C6-C11 aromatic alkyl groups (e.g., C6 aromatic alkyl, C7 aromatic alkyl, C8 aromatic alkyl, C9 aromatic alkyl, C10 aromatic alkyl, C11 aromatic alkyl, etc.).

[0015] Preferably, R1 is selected from C9-C11 straight-chain alkyl (e.g., it can be C9 straight-chain alkyl, C10 straight-chain alkyl, C11 straight-chain alkyl, etc.).

[0016] Preferably, R2 is selected from C8-20 straight-chain alkyl groups (e.g., C8 straight-chain alkyl, C9 straight-chain alkyl, C10 straight-chain alkyl, C11 straight-chain alkyl, C12 straight-chain alkyl, C13 straight-chain alkyl, C14 straight-chain alkyl, C15 straight-chain alkyl, C16 straight-chain alkyl, C17 straight-chain alkyl, C18 straight-chain alkyl, C19 straight-chain alkyl, C20 straight-chain alkyl, etc.) and C8-20 branched alkyl groups (e.g., C8 branched alkyl, C9 branched alkyl, C10 branched alkyl, C11 branched alkyl, C12 branched alkyl, etc.). The alkyl group, C13 branched alkyl group, C14 branched alkyl group, C15 branched alkyl group, C16 branched alkyl group, C17 branched alkyl group, C18 branched alkyl group, C19 branched alkyl group, C20 branched alkyl group, etc., or C8-20 silyl group (e.g., it can be C8 silyl group, C9 silyl group, C10 silyl group, C11 silyl group, C12 silyl group, C13 silyl group, C14 silyl group, C15 silyl group, C16 silyl group, C17 silyl group, C18 silyl group, C19 silyl group, C20 silyl group, etc.).

[0017] Preferably, R2 is selected from any one of the following structures: Preferably, R3 and R4 are each independently selected from any one of hydrogen, fluorine, chlorine, bromine, C4-C8 straight-chain alkyl (e.g., C4 straight-chain alkyl, C5 straight-chain alkyl, C6 straight-chain alkyl, C7 straight-chain alkyl, C8 straight-chain alkyl, etc.), C4-C8 branched alkyl (e.g., C4 branched alkyl, C5 branched alkyl, C6 branched alkyl, C7 branched alkyl, C8 branched alkyl, etc.), thiophene, halothiophene, benzene ring, or halobenzene ring.

[0018] In this invention, the receptor unit is selected from any of the following structures, wherein Indicates the connection location of the body element: ; R5 and R6 are independently selected from any one of H, F, or Cl.

[0019] In this invention, the receptor unit shown is selected from any of the following structures: .

[0020] In this invention, the donor unit and the acceptor unit can be freely combined to obtain organic small molecule photovoltaic materials based on benzopyrazine donor cores.

[0021] Preferably, the organic small molecule photovoltaic material based on benzopyrazine donor core is selected from any one of the following M1-M6: .

[0022] In this invention, the raw materials for preparing the donor unit shown in Formula I include any one of the compounds shown in Formula III-1 or Formula III-2 and any one of the compounds shown in Formula IV-1 or Formula IV-2: ; In Formula III, R1 and R2 are defined the same as those in Formula I, and in Formula IV, R3 and R4 are defined the same as those in Formula I.

[0023] Preferably, the molar ratio of the compound shown in Formula III-1 or Formula III-2 to the compound shown in Formula IV-1 or Formula IV-2 is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, etc.

[0024] In a second aspect, the present invention provides a method for preparing organic small molecule photovoltaic materials based on benzopyrazine donor cores as described in the first aspect, the preparation method comprising the following steps: (1) The raw materials for preparing the donor unit shown in Formula III-1 or Formula III-2 are mixed with trifluorophenylboronic acid shown in Formula IV, and the mixture is subjected to a Suzuki reaction to obtain compounds of Formula i-1 and Formula i-2, as shown in the following reaction formulas: (2) The donor unit, VHA reagent, and halogenating agent shown in formula i-1 or i-2 are mixed and reacted to obtain a dialdehyde-terminated compound, as shown in the following reaction formula: Wherein, the aldehyde group of the dialdehyde end-group compound is attached to the donor unit shown in Formula I. Place (3) The dialdehyde end-group compound obtained in step (2) is reacted with the acceptor compound to obtain the organic small molecule photovoltaic material based on the benzopyrazine donor core, and the reaction formula is shown below: R0 is selected from bromine atoms. EG is selected from The carbon atom at the position of the asterisk is the carbon atom shared by the double bond connected to EG; The receptor compound is any one of the following compounds: .

[0025] In this invention, DMF ( N,N(-dimethylformamide), EDC (1,2-dichloroethane), pyridine.

[0026] In this invention, the molar ratio of the raw materials for preparing the donor unit shown in Formula III-1 or Formula III-2 to the compound shown in Formula IV is 1:(1.5-2.5), for example, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.3 or 1:2.5, etc.

[0027] Preferably, the reaction in step (1) is carried out in the presence of a catalyst, preferably tris(dibenzylidene indeneacetone)palladium.

[0028] Preferably, the molar ratio of the raw material to the catalyst in the donor unit shown in Formula III-1 or Formula III-2 is 1:0.06-0.20, for example, 1:0.06, 1:0.08, 1:0.1, 1:0.12, 1:0.14, 1:0.16, 1:0.18, 1:0.2, 1:0.22 or 1:0.2, etc.

[0029] Preferably, the reaction in step (1) is carried out in the presence of a ligand, preferably tris(o-tolyl)phosphine.

[0030] Preferably, the molar ratio of the raw material to the ligand in the preparation of the donor unit shown in Formula III-1 or Formula III-2 is 1:0.24-0.35, for example, 1:0.24, 1:0.26, 1:0.28, 1:0.3, 1:0.32, 1:0.34 or 1:0.35, etc.

[0031] Preferably, the reaction in step (1) is carried out in the presence of a base, preferably potassium carbonate.

[0032] Preferably, the molar ratio of the raw material to the alkali in the donor unit shown in Formula III-1 or Formula III-2 is 1:4-10, such as 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, 1:7.5, 1:8, 1:9, 1:9.5 or 1:10.

[0033] Preferably, in step (1), the catalyst reagent includes Pd2(bda)3.

[0034] Preferably, in step (1), the ligand reagent includes P(o-toly)3.

[0035] Preferably, in step (1), the alkaline reagent includes K2CO3.

[0036] Preferably, in step (1), the mixing temperature is 0-25℃, for example, it can be 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, etc.; preferably, it is 0-5℃, for example, it can be 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, etc.

[0037] Preferably, in step (1), the reaction temperature is 70-95℃, for example, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, etc.; preferably 80-85℃, for example, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, etc.

[0038] Preferably, in step (1), the reaction time is 10-24 h, for example, 10 h, 14 h, 16 h, 22 h, etc.; preferably, it is 10-12 h, for example, 10 h, 11 h, 12 h, etc.

[0039] Preferably, in step (1), the reaction is carried out in a tetrahydrofuran solvent.

[0040] Preferably, in step (1), the reaction is carried out in a protective gas atmosphere, wherein the protective gas includes any one of nitrogen, argon or helium.

[0041] In this invention, in step (2), the molar ratio of the donor unit, VHA reagent and halogenating agent is 1:(15-50):(15-50), for example, it can be 1:15:15, 1:17:20, 1:25:16, 1:30:45, 1:35:27, 1:40:44, 1:45:34, 1:50:50, etc.; preferably it is 1:(15-25):(15-25), for example, it can be 1:15:15, 1:16:20, 1:19:25, 1:21:15, 1:23:18, 1:25:25, etc.

[0042] Preferably, in step (2), the VHA reagent includes DMF.

[0043] Preferably, in step (2), the halogenating agent includes any one or a combination of at least two of POCl3, COCl2 or SOCl2, preferably POCl3.

[0044] Preferably, in step (2), the mixing temperature is 0-25℃, for example, it can be 0℃, 5℃, 10℃, 15℃, 20℃, 25℃, etc.; preferably, it is 0-5℃, for example, it can be 0℃, 1℃, 2℃, 3℃, 4℃, 5℃, etc.

[0045] Preferably, in step (2), the reaction temperature is 50-85℃, for example, it can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, etc.; preferably, it is 75-85℃, for example, it can be 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, etc.

[0046] Preferably, in step (2), the reaction time is 18-48 h, for example, 18 h, 28 h, 38 h, 48 h, etc.; preferably, it is 18-22 h, for example, 18 h, 19 h, 20 h, 21 h, 22 h, etc.

[0047] Preferably, in step (2), the reaction is carried out in a chlorinated solvent, which includes any one or a combination of at least two of 1,2-dichloroethane, dichloromethane or trichloromethane, preferably 1,2-dichloroethane.

[0048] Preferably, in step (2), the reaction is carried out in a protective gas atmosphere, the protective gas including any one of nitrogen, argon or helium.

[0049] In this invention, in step (2), after the reaction is completed, the reaction solution is cooled to room temperature and then added dropwise to methanol to precipitate. The precipitate is collected by centrifugation. Then, the mixture of petroleum ether and dichloromethane in a volume ratio of 3:1 with low polarity is purified by silica gel chromatography. The organic solvent is removed by rotary evaporation to obtain a relatively pure dialdehyde end-group compound.

[0050] Preferably, in step (3), the molar ratio of the dialdehyde end-group compound and the acceptor compound is 1:(2-10), for example, it can be 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, etc., and preferably 1:(4-8), for example, it can be 1:4, 1:5, 1:6, 1:7, 1:8, etc.

[0051] Preferably, in step (3), the reaction temperature is 30-65℃, for example, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, etc.; preferably 60-65℃, for example, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, etc.

[0052] Preferably, in step (3), the reaction time is 8-24 h, for example, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, etc.; preferably 8-10 h, for example, 8 h, 9 h, 10 h, etc.

[0053] Preferably, in step (3), the reaction is carried out under an alkaline catalyst, which includes any one of triethylamine, pyridine or piperidine, preferably pyridine.

[0054] Preferably, the mass ratio of the dialdehyde end-group compound to the alkaline catalyst is (6-8):100, for example, 6:100, 7:100, 8:100, etc.; more preferably, it is (7.5-8):100, for example, 7.5:100, 7.6:100, 7.7:100, 7.8:100, 7.9:100, 8:100, etc.

[0055] Preferably, in step (3), the reaction is carried out in a solvent, which includes any one or a combination of at least two of 1,2-dichloroethane, dichloromethane or trichloromethane, preferably trichloromethane.

[0056] In this invention, in step (3), after the reaction is completed, the reaction solution is cooled to room temperature, and then the reaction solution is added dropwise to methanol to precipitate. The precipitate is collected by centrifugation. Then, the mixture of petroleum ether and dichloromethane in a volume ratio of 1:1 with low polarity is purified by silica gel chromatography, and the organic solvent is removed by rotary evaporation to obtain the organic small molecule photovoltaic material based on benzopyrazine donor core.

[0057] In this invention, the method for preparing the donor unit shown in Formula I includes the following steps: The preparation methods of the donor unit compounds shown in Formula I-1 and Formula I-2 include the following steps: (a) The compound shown in Formula II is mixed with a reducing agent and reacted to obtain an intermediate; (b) The intermediate obtained in step (a) is mixed with the compound shown in formula III and reacted to obtain intermediate 2; (c) The intermediate 2 obtained in step (b) is mixed with the trifluorophenylboronic acid compound and subjected to a suzuki reaction to obtain the donor unit compounds shown in Formula I-1 and Formula I-2; .

[0058] In this invention, in step (a), the molar ratio of the compound represented by Formula II to the reducing agent is 1:(10-40), for example, it can be 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, etc.; preferably it is 1:(30-40), for example, it can be 1:30, 1:32, 1:34, 1:36, 1:38, 1:40, etc.

[0059] Preferably, in step (a), the reducing agent comprises zinc powder.

[0060] Preferably, in step (a), the reaction temperature is 40-85℃, for example, it can be 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, etc., preferably 80-85℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, etc.

[0061] Preferably, in step (a), the reaction time is 24-48 h, for example, 24 h, 30 h, 36 h, 42 h, 48 h, etc.; more preferably, it is 44-48 h, for example, 44 h, 45 h, 46 h, 47 h, 48 h, etc.

[0062] Preferably, in step (a), the reaction is carried out in a solvent, which includes glacial acetic acid.

[0063] Preferably, in step (a), the reaction is carried out in a protective gas atmosphere, the protective gas including any one of nitrogen, argon or helium.

[0064] In this invention, in step (a), after the reaction is completed, the reaction solution obtained after the reaction is cooled to room temperature, then washed with sodium chloride aqueous solution, dried with anhydrous magnesium sulfate, the solvent is evaporated under vacuum, and then purified by silica gel chromatography column to obtain an intermediate (yellowish-brown liquid).

[0065] Preferably, in step (b), the molar ratio of the intermediate to the compound shown in Formula III is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.7, 1:1.9, 1:2.1, 1:2.3, 1:2.5, etc.

[0066] Preferably, in step (b), the reaction temperature is 25-85°C, for example, it can be 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, etc.

[0067] Preferably, in step (b), the reaction time is 24-48 h, for example, 24 h, 30 h, 36 h, 42 h, 48 h, etc.

[0068] Preferably, in step (c), the molar ratio of the intermediate to the trifluorophenylboronic acid compound is 1:(1.5-2.5), for example, it can be 1:1.5, 1:1.7, 1:1.9, 1:2.1, 1:2.3, 1:2.5, etc.

[0069] Preferably, in step (c), the reaction temperature is 70-95°C, for example, it can be 80°C, 95°C, 90°C, 95°C, etc.

[0070] Preferably, in step (c), the reaction time is 10-24 h, for example, 12 h, 14 h, 16 h, 24 h, etc.

[0071] Preferably, the reaction in step (c) is carried out in the presence of a catalyst.

[0072] Preferably, the molar ratio of the intermediate to the catalyst in step (c) is 1:(0.04-0.08), such as 1:0.04, 1:0.05, 1:0.06, 1:0.07 or 1:0.08.

[0073] Preferably, the reaction in step (c) is carried out in the presence of a ligand.

[0074] Preferably, the molar ratio of the intermediate to the ligand in step (c) is 1:(0.24-0.40), for example, 1:0.24, 1:0.26, 1:0.28, 1:0.3, 1:0.32, 1:0.34, 1:0.36, 1:0.38 or 1:0.4, etc.

[0075] Preferably, the reaction in step (c) is carried out in the presence of a base.

[0076] Preferably, the molar ratio of the intermediate to the base in step (c) is 1:(4-6), such as 1:4, 1:4.3, 1:4.6, 1:4.9, 1:5.2, 1:5.5, 1:5.8 or 1:6.

[0077] Preferably, in step (c), the catalyst is tetrakis(triphenylphosphine) or tris(dibenzylidene indenacetone)palladium.

[0078] Preferably, in step (c), the catalyst is tris(dibenzylidene indenacetone)palladium.

[0079] Preferably, in step (c), the ligand is triphenylphosphine or tris(o-tolyl)phosphine.

[0080] Preferably, in step (c), the ligand is tris(o-tolyl)phosphine.

[0081] Preferably, in step (c), the reaction temperature is 70-95°C, for example, 70°C, 75°C, 80°C, 85°C or 95°C.

[0082] Preferably, in step (c), the reaction temperature is 80-85°C, such as 80°C, 81°C, 1:82°C, 83°C, or 85°C.

[0083] Preferably, in step (c), the reaction time is 10-24 h, such as 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h.

[0084] Preferably, in step (c), the reaction time is 10-12 h, such as 10 h, 10.5 h, 11 h, 11.5 h or 12 h.

[0085] Preferably, in step (c), the reaction is carried out in a solvent, wherein the solvent is tetrahydrofuran.

[0086] Preferably, in step (c), the reaction is carried out in a protective gas atmosphere, wherein the protective gas is any one of nitrogen, argon or helium.

[0087] In this invention, in step (c), after the reaction is completed, the reaction solution is cooled to room temperature, the crude product is precipitated, the precipitated crude product is collected by centrifugation, and then purified by silica gel chromatography with a mixed solvent of petroleum ether and dichloromethane in a volume ratio of 4:1 with low polarity. The organic solvent is removed by rotary evaporation to obtain a relatively pure donor unit shown in Formula I.

[0088] As a preferred embodiment of the present invention, the method for preparing the organic small molecule photovoltaic material based on benzopyrazine donor core includes the following steps: (A) Mix any one of the compounds shown in Formula III with zinc powder and react at 40-85°C (e.g., 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or 85°C, etc.) for 24-48 h (e.g., 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h or 48h, etc.) to obtain an intermediate; (B) The intermediate obtained in step (A) is mixed with the compound shown in Formula IV and reacted at 25-85°C (e.g., 25°C, 33°C, 41°C, 49°C, 57°C, 65°C, 73°C or 85°C, etc.) for 24-48 h (e.g., 24h, 26h, 28h, 30h, 32h, 34h, 36h, 38h, 40h or 48h, etc.) to obtain the intermediate shown in Formula V.

[0089] (C) The intermediate obtained in step (B) is mixed with the compound shown in formula VI, and the catalyst tris(dibenzylidene indeneacetone)dipalladium is added. The molar ratio of the ligand tris(o-tolyl)phosphine and the base potassium carbonate is 1:(1-1.5):(0.06):(0.24):(4-10). The mixture is reacted for 12-24 h to obtain the donor unit of formula I.

[0090] The donor unit of formula I obtained in step (C), DMF, and phosphorus oxychloride are mixed at 0-25°C (e.g., 0°C, 5°C, 10°C, 15°C, or 25°C) and reacted at 50-85°C (e.g., 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, or 85°C) for 18-48 h (e.g., 18h, 22h, 26h, 30h, 34h, 38h, 42h, or 48h) to obtain a dialdehyde-terminated compound, as shown in the following reaction formula: Wherein, the aldehyde group of the dialdehyde end-group compound is attached to the donor unit shown in Formula I. Place; (D) The dialdehyde end-group compound obtained in step (C), the acceptor unit shown in Formula II, and the basic catalyst are mixed and reacted at 30-65°C (e.g., 30°C, 38°C, 45°C, 50°C, 60°C, or 65°C, etc.) for 8-24 h (e.g., 8h, 10h, 12h, 14h, 16h, 18h, 20h, or 24h, etc.) to obtain the organic small molecule photovoltaic material based on the benzopyrazine donor core, as shown in the following reaction formula: In this invention, the synthesis route of the donor unit is as follows: or In this invention, the synthetic route for the dialdehyde-terminated compound is as follows: Thirdly, the present invention provides an application of organic small molecule photovoltaic materials based on benzopyrazine donor cores as described in the first aspect in the fabrication of photovoltaic devices.

[0091] In this invention, the photovoltaic device includes an organic solar cell.

[0092] Preferably, the active layer of the organic solar cell includes a donor material and an acceptor material; the acceptor material includes the organic small molecule photovoltaic material based on a benzopyrazine donor core; the donor material includes a polymer donor material and / or a small molecule donor material.

[0093] Preferably, the polymer donor material includes D18, PM6.

[0094] Preferably, the small molecule donor material includes D18.

[0095] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention applies donor units and acceptor units with good planar structure to the design and synthesis of soluble organic small molecule photovoltaic materials, and obtains a series of acceptor small molecules with good planarity and good crystallization ability; this invention is the first to synthesize planar acceptor units and apply them to photovoltaic materials.

[0096] (2) This invention uses the core of the Y6 intermediate backbone of the traditional acceptor small molecule as the intermediate donor unit and controls the amount of trifluorobenzene by bromine substitution to synthesize organic small molecule photovoltaic materials based on benzopyrazine donor cores. Such organic small molecule photovoltaic materials have good crystallinity and good solubility in common organic solvents (tetrahydrofuran, dichloromethane, trichloromethane, etc.), and can be used to prepare high-performance organic solar cells by solution method. At the same time, these soluble organic small molecule photovoltaic materials have good stacking on the film, and the absorption of the film has a significant red shift relative to the solution.

[0097] (3) The organic small molecule photovoltaic material based on benzopyrazine donor core synthesized in this invention has the advantage of matching HOMO and LUMO energy levels with the donor material as an acceptor material; and such organic small molecule acceptor materials do not have batch differences and have good reproducibility.

[0098] (3) The organic small molecule photovoltaic material based on benzopyrazine donor core provided by the present invention, when used as an acceptor material, has an energy conversion efficiency of over 18% and an open circuit voltage of over 0.94 eV when blended with polymer donor material D18, and the energy loss is reduced to 0.502 eV. Attached Figure Description

[0099] Figure 1 The UV-Vis absorption spectra of M1 were measured in chloroform solution and in thin film condition.

[0100] Figure 2 The UV-Vis absorption spectra of M2 were measured in chloroform solution and in thin film condition.

[0101] Figure 3 Cyclic voltammetry curves measured by the M1 electrochemical method.

[0102] Figure 4 Cyclic voltammetry curves measured by the M2 electrochemical method.

[0103] Figure 5 This demonstrates a soluble organic small molecule solar cell device with the structure ITO / PEDOT:PSS / PM6:M1 / PDINO / Al. JV curve.

[0104] Figure 6This demonstrates a soluble organic small molecule solar cell device with the structure ITO / PEDOT:PSS / PM6:M2 / PDINO / Al. JV curve.

[0105] Figure 7A This is a front view of the molecular stacking pattern between the M1 donor and acceptor units.

[0106] Figure 7B This is a top view of the molecular stacking pattern between the M1 donor and acceptor units.

[0107] Figure 7C This is a side view of the molecular stacking pattern between the M1 donor and acceptor units.

[0108] Figure 8A This is a front view of the molecular stacking pattern between M1 receptor units.

[0109] Figure 8B A top view of the molecular stacking pattern between M1 receptor units.

[0110] Figure 8C A side view of the molecular stacking pattern between M1 receptor units.

[0111] Figure 9A This is a front view of the molecular stacking pattern between the M2 donor and acceptor units.

[0112] Figure 9B This is a top view of the molecular stacking pattern between the M2 donor and acceptor units.

[0113] Figure 9C A side view of the molecular stacking pattern between the M2 donor and acceptor units.

[0114] Figure 10A A front view of the molecular stacking pattern between M2 receptor units.

[0115] Figure 10B This is a top view of the molecular stacking pattern between M1 receptor units.

[0116] Figure 10C A side view of the molecular stacking pattern between M2 receptor units. Detailed Implementation

[0117] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0118] In the following examples, the heating temperatures mentioned refer to the temperatures of the heating medium.

[0119] Example 1 This embodiment provides an organic small molecule photovoltaic material M1 based on a benzopyrazine donor core, and the synthetic route is shown below: (1) Compound 37 (1.00 g, 0.923 mmol) was dissolved in 100 mL of glacial acetic acid and mixed with activated zinc powder (2.40 g, 36.91 mmol) under nitrogen protection. The mixture was heated to 85 °C and reacted for 48 h. The reaction solution was cooled to room temperature and then dissolved in dichloromethane. The solution was then extracted with a saturated aqueous solution of sodium chloride, dried over anhydrous magnesium sulfate, and the solvent was removed by vacuum evaporation. The solution was then purified by silica gel column chromatography (eluent: dichloromethane) to obtain an intermediate (yellowish-brown liquid). The intermediate was then reacted with compound 38 (776 mg, 3.69 mmol) in glacial acetic acid solution at 85 °C for 48 h. The reaction solution was cooled to room temperature, and the crude product of compound 39 precipitated. The precipitated crude product was collected by centrifugation and purified by silica gel column chromatography (V... 石油醚 :V 二氯甲烷 =4:1), yielding compound 39 (451 mg, 0.369 mmol), with a yield of 40.1%; (2) Under a nitrogen atmosphere, compound 39 (260 mg, 0.183 mmol) was dissolved in 20 mL of tetrahydrofuran at a reaction temperature of 85 °C. Then, reactants 3,4,5-trifluorophenylboronic acid (64.42 mg, 0.366 mmol), tris(dibenzylindeneacetone)dipalladium (10 mg, 0.011 mmol), tris(o-tolyl)phosphine (13.36 mg, 0.471 mmol), and potassium carbonate (101 mg, 0.732 mmol) were added in the above molar ratio and reacted for 12-24 h. The reaction solution was cooled to room temperature, and the crude product of compound 40 precipitated. The precipitated crude product was collected by centrifugation and purified using silica gel column chromatography (V... 石油醚 :V 二氯甲烷 =4:1), yielding compound 40 (200 mg, 0.141 mmol), in a yield of 77.1%.

[0120] (3) Under nitrogen atmosphere protection, DMF (0.25 mL) and phosphorus oxychloride (0.25 mL) were added dropwise to a low-temperature protected (0 °C) solution of compound 40 (200 mg, 0.141 mmol) in 1,2-dichloroethane (20 mL), and the mixture was refluxed for 18 h. The reaction solution was cooled to room temperature, and then added dropwise to methanol. The solid precipitate was collected and purified by silica gel column chromatography (V). 石油醚 :V二氯甲烷 The ratio of the two solutions was 3:1, yielding compound 41 (176 mg, 0.119 mmol), with a yield of 84.39%. (4) Compound 41 (176 mg, 0.119 mmol) obtained in step (2) was mixed with compound 41-1 (253 mg, 1.10 mmol) in chloroform solution, and pyridine (2200 mg) was added dropwise. The mixture was refluxed for 10 h. The reaction solution was cooled to room temperature, and then added dropwise to methanol. The solid precipitate was collected and purified by silica gel column chromatography (V). 石油醚 :V 二氯甲烷 The ratio of the two solutions was 1:1, yielding compound M1 (183 mg, 0.094 mmol) in a yield of 78.8%.

[0121] Structural identification: M1 1 H NMR (400 MHz, CDCl3) δ 9.41 (s, 2H), 9.00 (s, 2H), 8.67 (s, 2H), 8.21 (s, 2H), 7.92 (d, J = 44.5 Hz, 3H), 7.62 - 7.34 (m, 4H), 4.97 (s, 4H), 3.26 (s, 4H), 2.47 (s, 2H), 1.91 (s, 4H), 1.71 - 0.68 (m, 102H). MALDI-TOF MS (m / z): 1951.736.

[0122] Example 2 (1) Compound 43 (1.00 g, 0.923 mmol) was dissolved in 100 mL of glacial acetic acid and mixed with activated zinc powder (2.40 g, 36.91 mmol) under nitrogen protection. The mixture was heated to 85 °C and reacted for 48 h. The reaction solution was cooled to room temperature and then dissolved in dichloromethane. The solution was then extracted with a saturated aqueous solution of sodium chloride, dried over anhydrous magnesium sulfate, and the solvent was removed by vacuum evaporation. The solution was then purified by silica gel column chromatography (eluent: dichloromethane) to obtain an intermediate (yellowish-brown liquid). The intermediate was then reacted with compound 44 (1350.57 mg, 3.69 mmol) in glacial acetic acid solution at 85 °C for 48 h. The reaction solution was cooled to room temperature, and the crude product of compound 45 precipitated. The precipitated crude product was collected by centrifugation and purified by silica gel column chromatography (V 石油醚 :V 二氯甲烷The ratio of the two solutions was 4:1, yielding compound 45 (663 mg, 0.443 mmol), with a yield of 48.1%. (2) Under a nitrogen atmosphere, compound 45 (500 mg, 0.333 mmol) was dissolved in 20 mL of tetrahydrofuran at a reaction temperature of 85 °C. Then, reactants 3,4,5-trifluorophenylboronic acid (64.42 mg, 0.667 mmol), tris(dibenzylindeneacetone)dipalladium (19 mg, 0.020 mmol), tris(o-tolyl)phosphine (24.29 mg, 0.080 mmol), and potassium carbonate (183 mg, 1.332 mmol) were added in the above molar ratio and reacted for 12-24 h. The reaction solution was cooled to room temperature, and the crude product of compound 40 precipitated. The precipitated crude product was collected by centrifugation and purified using silica gel column chromatography (V... 石油醚 :V 二氯甲烷 The ratio of compound 4:1 was used to obtain compound 46 (367.7 mg, 0.230 mmol), with a yield of 69.1%.

[0123] (3) Under a nitrogen atmosphere, DMF (0.25 mL) and phosphorus oxychloride (0.25 mL) were added dropwise to a low-temperature protected (0 °C) solution of compound 40 (200 mg, 0.125 mmol) in 1,2-dichloroethane (20 mL), and the mixture was refluxed for 18 h. The reaction solution was cooled to room temperature, and then added dropwise to methanol. The solid precipitate was collected and purified by silica gel column chromatography (V). 石油醚 :V 二氯甲烷 =3:1), yielding compound 47 (180.50 mg, 0.109 mmol), in a yield of 87.20%; (4) Compound 47 (180 mg, 0.109 mmol) obtained in step (3) was mixed with compound 41-1 (253 mg, 1.10 mmol) in chloroform solution, and pyridine (2200 mg) was added dropwise. The mixture was refluxed for 10 h. The reaction solution was cooled to room temperature, and then added dropwise to methanol. The solid precipitate was collected. The precipitate was then purified by silica gel column chromatography (V 石油醚 :V 二氯甲烷 The ratio of the two solutions was 1:1, yielding compound M2 (179.4 mg, 0.094 mmol) in a yield of 86.3%.

[0124] Structural assessment: M2 1 H NMR (400 MHz, CDCl3) δ 9.49 (d, J= 8.2 Hz, 2H), 9.07(s, 2H), 8.70 (s, 2H), 8.34 (s, 2H), 8.00 (d, J = 8.7 Hz, 2H), 7.68 - 7.41(m, 6H), 4.92 (d, J = 7.5 Hz, 4H), 3.28 (s, 4H), 2.37 (s, 2H), 1.91 (s, 4H), 1.59 - 0.64 (m, 102H). MALDI-TOF MS (m / z): 2081.823.

[0125] Test Example 1 The UV-Vis absorption spectra of small molecules M1 and M2 in chloroform solution and thin film were measured, and the optical band gap of the polymer was calculated using empirical formulas.

[0126] Test method: Dissolve an appropriate amount of small molecule M1 or M2 in chloroform to prepare a solution of a certain concentration, and spin-coat a portion of the solution onto a quartz plate to form a uniform thin film.

[0127] like Figure 1 The image shows the UV-Vis absorption spectra of M1 measured in chloroform solution and in thin film condition. The absorption optical band gap is calculated using the formula (E...). g= The absorption margin (1240 / λ) was calculated, where the maximum absorption peak of M1 in chloroform solution is 746 nm. The film has a broad absorption range of 600-900 nm, with a maximum absorption peak of 785 nm and an absorption margin of 861 nm. The optical band gap is 1.44 eV. Moreover, the maximum absorption peak of the film is red-shifted by 39 nm relative to the solution, indicating that the molecules have good planarity and are well aggregated in the film.

[0128] like Figure 2 The image shows the UV-Vis absorption spectra of M2 measured in chloroform solution and in thin film. The absorption optical band gap was calculated using the formula (Eg = 1240 / λ absorption margin). The maximum absorption peak of M2 in chloroform solution is 742 nm, while the thin film exhibits broad absorption in the 600-900 nm range, with a maximum absorption peak at 778 nm and an absorption margin at 857 nm, resulting in an optical band gap of 1.45 eV. Furthermore, the maximum absorption peak of the film is redshifted by 36 nm relative to that in solution, indicating good molecular planarity and good aggregation within the film.

[0129] Test Example 2 Cyclic voltammetry curves of small molecules M1 and M2 in thin film state were determined. Test method: Apply a chloroform solution of M1 or M2 onto a platinum electrode, using Ag / Ag+ As a reference electrode, after drying and forming a film, it was placed in an acetonitrile solution of tetrabutylammonium hexafluorophosphate for measurement. The initial oxidation potential and initial reduction potential were obtained from the graph, and then E was calculated using the formula. HOMO =-e(E ox onset +4.71)(eV), E LUMO = -e(E red onset +4.71) (eV), the HOMO and LUMO energy levels of compounds M1 and M2 were calculated.

[0130] like Figure 3 The figure shows the cyclic voltammogram based on the M1 thin film; it can be seen from the figure that the initial oxidation potential of M1 is 0.90 eV and the initial reduction potential is -0.89 eV; the calculated E... HOMO =-5.61 eV, E LUMO = -3.82 eV.

[0131] like Figure 4 The figure shows the cyclic voltammogram based on the M2 thin film; it can be seen from the figure that the initial oxidation potential of M2 is 1.02 eV and the initial reduction potential is -0.85 eV; the calculated Et is... HOMO =-5.73 eV, E LUMO = -3.86 eV.

[0132] Test Example 3 Photovoltaic property testing of M1 Test method: Conventional forward organic solar cell devices were fabricated by solution spin coating using M1 or M2 as acceptors and polymer D18 as donors. The device structure was ITO / PEDOT:PSS / D18:M1 / PDINN / Al or ITO / PEDOT:PSS / D18:M2 / PDINN / Al.

[0133] The preparation method is as follows: M1 or M2 is mixed with an equal mass of D18 and dissolved in chloroform to obtain a 10 mg / mL solution. Organic solar cells are fabricated on a transparent silver-tin oxide (ITO) coated glass substrate. The transparent conductive glass substrate with ITO is ultrasonically cleaned with detergent, deionized water, ethanol, and isopropanol, and then the substrate surface is treated with ozone. PEDOT:PSS is spin-coated onto the ITO at a speed of 3000-4000 rpm and dried at 150℃ for 15 min to obtain an anode modification layer with a thickness of 30 nm. In a glove box, chloroform solution is uniformly spin-coated onto the anode modification layer at a speed of 1800-4000 rpm to obtain an active material layer with a thickness of 80-200 nm. After hot annealing on a hot stage at 100℃ for 10 min, the cathode modification layer PDINN is uniformly spin-coated onto the active layer. Finally, 2×10 -6 Al was deposited onto the cathode modification layer under a vacuum of Pa to form a cathode with a thickness of 80 nm, thus obtaining an organic solar cell device. A 500 W xenon lamp combined with an AM1.5 filter was used as a white light source to simulate sunlight, and the light intensity at the device measurement point was adjusted to 100 mW / cm². -2 Keithley was used to test three parameters of the fabricated polymer solar cell device: open-circuit voltage, short-circuit current, and fill factor.

[0134] Figure 5 and Figure 6 The figures are the current-voltage diagrams based on the molecular devices M1 and M2, respectively.

[0135] Table 1 As shown in Table 1, both M1 and M2 have the characteristics of high open-circuit voltage, high short-circuit current density, high fill factor and high photoelectric conversion efficiency.

[0136] Energy loss calculation: The testing method is as follows: Energy loss mainly consists of three parts. The bandgap can be obtained by integrating and differentiating the EQE spectrum; ΔE1, the invisible and avoidable energy loss, is obtained by subtracting the device voltage from the limiting voltage under the material's bandgap; ΔE2 is the radiation loss obtained from the material's electroluminescence properties and detailed EQE data; ΔE3 is the EQE loss obtained from the electroluminescence properties. EL Substitute into the formula Δ E 3= q ΔV OC non-rad = - k B T ln (EQE EL )get.

[0137] The test results are shown in Table 2: Table 2 As shown in Table 2, M1 has the characteristic of low energy loss.

[0138] Test Example 4 Acquisition of single-crystal structures of molecules M1 and M2 Single crystal acquisition method: M1 or M2 molecular single crystals are grown at room temperature using a liquid-phase diffusion method. An appropriate amount of methanol is transferred to a chloroform solution containing concentrated M1 or M2; over time, the chloroform solution will crystallize. Single crystal diffraction is collected at low temperature under liquid nitrogen protection according to standard procedures using a single-crystal X-ray diffractometer (model XtaLAB PRO 007HF(Mo) manufactured by Rigaku Corporation, Japan) to reduce X-ray radiation damage.

[0139] like Figure 7A , Figure 7B and Figure 7C As shown in the diagram, the M1 donor and acceptor units are arranged in a π-π packing pattern. The distance between the faces is 3.50 Å. Figure 8A , Figure 8B and Figure 8C As shown, the M1 receptor unit is arranged in a π-π stacking pattern, and the distance between the surfaces is 3.33 Å.

[0140] like Figure 9A , Figure 9B and Figure 9C As shown in the diagram, the M2 donor and acceptor units are arranged in a π-π packing pattern. The distance between the faces is 3.65 Å. Figure 10A , Figure 10B and Figure 10C As shown, the M2 receptor unit is arranged in a π-π stacking pattern with the receptor unit. It can be seen from the figure that the distance between the surfaces is 3.75 Å.

[0141] The applicant declares that the above embodiments illustrate the organic small molecule photovoltaic materials, their preparation methods, and applications, but the present invention is not limited to the above embodiments, i.e., it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection and disclosure scope of the present invention.

Claims

1. An organic small-molecule photovoltaic material based on a benzopyrazine donor core, characterized in that, The organic small molecule photovoltaic material has the following structure: ； Where D is the donor unit and A is the acceptor unit; The donor unit is selected from any one of the structures shown in Equation I-1 or Equation I-2, wherein Indicates the receptor unit connection location: ； Wherein, R1 is selected from any one of alkyl or acetal groups; R2 is selected from alkyl or silyl groups; R3 and R4 are each independently selected from any one of hydrogen, halogen, alkyl, substituted or unsubstituted thiophene, substituted or unsubstituted benzene ring; the number of carbon atoms of the alkyl, acetal, and silyl groups mentioned above is 5-20; X1-X3 are each independently selected from sulfur or selenium atoms.

2. The organic small molecule photovoltaic material based on benzopyrazine donor core according to claim 1, characterized in that, The given unit is selected from any of the following structures, wherein Indicates the connection location of the body element: 。 3. The organic small molecule photovoltaic material based on benzopyrazine donor core according to claim 1 or 2, characterized in that, R1 is selected from any one of C6-C11 straight-chain alkyl, C6-C11 branched alkyl, C6-C11 alcohol group or C6-C11 aromatic alkyl, preferably C9-C11 straight-chain alkyl; Preferably, R2 is selected from any one of C8-20 straight-chain alkyl, C8-20 branched alkyl, or C8-20 silane; Preferably, R2 is selected from any one of the following structures: ； Preferably, R3 and R4 are each independently selected from any one of hydrogen, fluorine, chlorine, bromine, C4-C8 straight-chain alkyl, C4-C8 branched alkyl, thiophene, halothiophene, benzene ring or halobenzene ring.

4. The organic small molecule photovoltaic material based on a benzopyrazine donor core according to any one of claims 1-3, characterized in that, The receptor unit is selected from any of the structures shown below, wherein Indicates the connection location: ； Among them, R5 and R6 are independently selected from any one of H, F or Cl; Preferably, the receptor unit shown is selected from any of the following structures: 。 5. The organic small molecule photovoltaic material based on a benzopyrazine donor core according to any one of claims 1-4, characterized in that, The organic small molecule photovoltaic material based on benzopyrazine donor cores is selected from any one of the following M1-M6: 。 6. The method for preparing organic small molecule photovoltaic materials based on benzopyrazine donor cores according to any one of claims 1-5, characterized in that, The preparation method includes the following steps: (1) The raw materials for preparing the donor unit shown in Formula III-1 or Formula III-2 are mixed with trifluorophenylboronic acid shown in Formula IV, and the mixture is subjected to a Suzuki reaction to obtain compounds of Formula i-1 and Formula i-2, as shown in the following reaction formulas: (2) The donor unit, VHA reagent, and halogenating agent shown in formula i-1 or i-2 are mixed and reacted to obtain a dialdehyde-terminated compound, as shown in the following reaction formula: ； (3) The dialdehyde end-group compound obtained in step (2) is reacted with the acceptor compound to obtain the organic small molecule photovoltaic material based on the benzopyrazine donor core, and the reaction formula is shown below: Where R0 is selected from bromine atoms EG is selected from The carbon atom at the position of the asterisk is the carbon atom shared by the double bond connected to EG; The receptor compound is any one of the following compounds: 。 7. The preparation method according to claim 6, characterized in that, The molar ratio of the raw materials for preparing the donor unit shown in Formula III-1 or Formula III-2 to the compound shown in Formula IV is 1:(1.5-2.5); Preferably, the reaction in step (1) is carried out in the presence of a catalyst, preferably tris(dibenzylidene indenacetone)palladium; Preferably, the molar ratio of the raw materials to the catalyst in the donor unit shown in Formula III-1 or Formula III-2 is 1:0.06-0.20; Preferably, the reaction in step (1) is carried out in the presence of a ligand, preferably tris(o-tolyl)phosphine; Preferably, the molar ratio of the raw material to the ligand in the donor unit shown in Formula III-1 or Formula III-2 is 1:0.24-0.35; Preferably, the reaction in step (1) is carried out in the presence of a base, preferably potassium carbonate; Preferably, the molar ratio of the raw material to the alkali in the preparation of the donor unit shown in Formula III-1 or Formula III-2 is 1:4-10; Preferably, in step (1), the mixing temperature is 0-25°C; Preferably, in step (1), the mixing temperature is 0-5°C; Preferably, in step (1), the reaction temperature is 70-95°C; Preferably, in step (1), the reaction temperature is 80-85℃; Preferably, in step (1), the reaction time is 10-24 h; Preferably, in step (1), the reaction time is 10-12 h; Preferably, in step (1), the reaction is carried out in any one or a combination of two of tetrahydrofuran or toluene solvent; Preferably, in step (1), the reaction is carried out in tetrahydrofuran; Preferably, in step (1), the reaction is carried out in a protective gas atmosphere, wherein the protective gas is any one of nitrogen, argon or helium.

8. The preparation method according to claim 6, characterized in that, In step (2), the VHA reagent is DMF, and the halogenating reagent is any one or a combination of at least two of POCl3, COCl2 or SOCl2; Preferably, in step (2), the molar ratio of the raw materials, VHA reagent and halogenating agent of the donor unit shown in Formula III-1 or Formula III-2 is 1:(15-25):(15-25); Preferably, in step (2), the halogenating agent is POCl3; Preferably, in step (2), the mixing temperature is 0-25°C; Preferably, in step (2), the mixing temperature is 0-5℃; Preferably, in step (2), the reaction temperature is 50-85℃; Preferably, in step (2), the reaction temperature is 75-85℃; Preferably, in step (2), the reaction time is 18-48 h; Preferably, in step (2), the reaction time is 18-22 h; Preferably, in step (2), the reaction is carried out in a chlorinated solvent, wherein the chlorinated solvent is any one or a combination of at least two of 1,2-dichloroethane, dichloromethane or trichloromethane; Preferably, in step (2), the reaction is carried out in a chlorinated solvent, wherein the chlorinated solvent is 1,2-dichloroethane; Preferably, in step (2), the reaction is carried out in a protective gas atmosphere, wherein the protective gas is any one of nitrogen, argon or helium; Preferably, in step (3), the molar ratio of the dialdehyde end-group compound to the acceptor compound is 1:(2-10); Preferably, in step (3), the molar ratio of the dialdehyde end-group compound to the acceptor compound is 1:(4-8); Preferably, in step (3), the reaction temperature is 30-65°C; Preferably, in step (3), the reaction temperature is 60-65°C; Preferably, in step (3), the reaction time is 8-24 h; Preferably, in step (3), the reaction time is 8-10 h; Preferably, in step (3), the reaction is carried out under an alkaline catalyst, which is any one of triethylamine, pyridine, or piperidine; Preferably, in step (3), the reaction is carried out under an alkaline catalyst, wherein the alkaline catalyst is pyridine; Preferably, the mass ratio of the dialdehyde end-group compound to the basic catalyst is (6-8):100; Preferably, the mass ratio of the dialdehyde end-group compound to the basic catalyst is (7.5-8):100; Preferably, in step (3), the reaction is carried out in a solvent, which is any one or a combination of at least two of 1,2-dichloroethane, dichloromethane or trichloromethane; Preferably, in step (3), the reaction is carried out in a solvent, and the solvent is chloroform.

9. The preparation method according to claim 6, characterized in that, The preparation methods of the donor unit compounds shown in Formula I-1 and Formula I-2 include the following steps: (a) The compound shown in Formula II is mixed with a reducing agent and reacted to obtain an intermediate; (b) The intermediate obtained in step (a) is mixed with the compound shown in formula III and reacted to obtain intermediate 2; (c) The intermediate 2 obtained in step (b) is mixed with the trifluorophenylboronic acid compound and subjected to a suzuki reaction to obtain the donor unit compounds shown in Formula I-1 and Formula I-2; ； Preferably, in step (a), the molar ratio of the compound represented by Formula II to the reducing agent is 1:(10-40); Preferably, in step (a), the molar ratio of the compound represented by Formula II to the reducing agent is 1:(30-40); Preferably, in step (a), the reducing agent is zinc powder or sodium borohydride; Preferably, in step (a), the reducing agent is zinc powder; Preferably, in step (a), the reaction temperature is 40-85°C; Preferably, in step (a), the reaction temperature is 80-85°C; Preferably, in step (a), the reaction time is 24-48 h; Preferably, in step (a), the reaction time is 44-48 h; Preferably, in step (a), the reaction is carried out in a solvent, wherein the solvent is glacial acetic acid; Preferably, in step (a), the reaction is carried out in a protective gas atmosphere, wherein the protective gas is any one of nitrogen, argon or helium; Preferably, in step (b), the molar ratio of the intermediate to the compound shown in Formula III is 1:(1.5-2.5); Preferably, in step (b), the molar ratio of the intermediate to the compound shown in Formula III is 1:1.5; Preferably, in step (b), the reaction temperature is 25-85°C and the reaction time is 24-48 h; Preferably, in step (c), the molar ratio of the intermediate to the trifluorophenylboronic acid compound is 1:(1.5-2.5); Preferably, in step (c), the molar ratio of the intermediate to the trifluorophenylboronic acid compound is 1:1.5; Preferably, the reaction in step (c) is carried out in the presence of a catalyst; Preferably, the molar ratio of the intermediate to the catalyst in step (c) is 1:(0.04-0.08); Preferably, the reaction in step (c) is carried out in the presence of a ligand; Preferably, the molar ratio of the intermediate to the ligand in step (c) is 1:(0.24-0.40). Preferably, the reaction in step (c) is carried out in the presence of a base; Preferably, the molar ratio of the intermediate to the base in step (c) is 1:(4-6). Preferably, in step (c), the catalyst is tetrakis(triphenylphosphine) or tris(dibenzylindenacetone)palladium. Preferably, in step (c), the catalyst is tris(dibenzylindenacetone)palladium; Preferably, in step (c), the ligand is triphenylphosphine or tris(o-tolyl)phosphine; Preferably, in step (c), the ligand is tris(o-tolyl)phosphine; Preferably, in step (c), the reaction temperature is 70-95°C; Preferably, in step (c), the reaction temperature is 80-85°C; Preferably, in step (c), the reaction time is 10-24 h; Preferably, in step (c), the reaction time is 10-12 h; Preferably, in step (c), the reaction is carried out in a solvent, wherein the solvent is tetrahydrofuran; Preferably, in step (c), the reaction is carried out in a protective gas atmosphere, wherein the protective gas is any one of nitrogen, argon or helium.

10. The application of an organic small molecule photovoltaic material based on a benzopyrazine donor core according to any one of claims 1-5 in the fabrication of photovoltaic devices; Preferably, the photovoltaic device includes an organic solar cell; Preferably, the active layer of the organic solar cell is composed of a donor material and an acceptor material; the acceptor material includes the organic small molecule photovoltaic material based on a benzopyrazine donor core as described in any one of claims 1-5; the donor material includes a polymer donor material and / or a small molecule donor material. Preferably, the polymer donor material is D18, PM6; Preferably, the small molecule donor material is D18.

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