Medium band gap receptor containing pentacyclic skeleton and preparation method and photovoltaic application thereof

Abstract

The invention relates to a medium band gap receptor containing a pentacyclic skeleton and a preparation method and photovoltaic application thereof. The structural formula of the receptor molecule is as shown in formula I, wherein Weak A is a weak electron withdrawing terminal group; ar is an aromatic group; and X is O, S, Se or Te. The optical band gap of the acceptor molecule is 1.55-2.00 eV, and the acceptor molecule mainly absorbs photons in near ultraviolet and visible light regions. A pentacyclic structure used by the receptor enables the receptor to be simple to synthesize and easy to modify, regulate and control, and the used weak electron-withdrawing end group enables the band gap to be widened and the LUMO to be improved by reducing the intramolecular charge transfer effect. A device prepared by matching the receptor with a proper donor can obtain high open-circuit voltage and high energy conversion efficiency. In addition, when the medium-band-gap acceptor material is applied to indoor organic photovoltaic and laminated organic solar cells, excellent photovoltaic performance can be obtained.

Description

Technical Field

[0001] The present invention belongs to the field of organic photovoltaics, and particularly relates to a class of medium-bandgap acceptors containing a pentacene backbone, a preparation method thereof, and applications in indoor organic photovoltaics and tandem organic solar cells. Background Art

[0002] As is well known, energy shortage and environmental pollution are two major problems that need to be solved urgently in human society at present: on the one hand, the fossil energy that human society strongly depends on for development is about to be exhausted, and on the other hand, the large amount of CO2 emitted by its use has caused a serious greenhouse effect. Therefore, the top priority is to develop new clean and renewable energy sources. Among many new energy sources, solar energy, as an inexhaustible and clean energy source, has received more and more attention. Organic solar cells can directly convert solar energy into electrical energy, and have the advantages of light weight, flexibility, semi-transparency, and the ability to prepare large-area devices by roll-to-roll process, and are being favored by researchers. Thanks to the continuous innovation of active layer materials, especially the development of non-fullerene acceptors, organic solar cells have developed rapidly, and their current power conversion efficiency has exceeded 19% (Adv. Mater, 2021, 33, e2102420; Joule, 2022, 6, 171; Angew. Chem. Int. Ed. 2023, 62, e2023126).

[0003] At present, the research on acceptors in the field of organic photovoltaics focuses on narrow-bandgap acceptors (optical absorption edge located in the near-infrared region), mainly because narrow-bandgap acceptors can expand the light absorption range of devices, which is beneficial to the improvement of device photocurrent. However, the power conversion efficiency of single-junction organic solar cells based on narrow-bandgap acceptors has reached a bottleneck, and new ways need to be explored to further improve device performance. On the other hand, narrow-bandgap acceptor materials cannot meet the requirements of new devices such as indoor photovoltaics because their absorption spectra do not match the indoor spectra.

[0004] Different from narrow-bandgap acceptors, electron acceptors with an absorption edge in the range of 620 - 800 nm and an optical bandgap of 1.55 - 2.00 eV are usually referred to as medium-bandgap acceptors. In the field of indoor organic photovoltaics, the absorption spectrum of medium-bandgap acceptor materials can highly match the emission spectrum of indoor light sources. Therefore, indoor organic photovoltaic devices based on medium-bandgap acceptor materials can utilize indoor light more efficiently and achieve higher energy conversion efficiencies. Moreover, such devices can serve as power sources for Internet of Things (IoT) devices such as wearable devices and smart homes, thus greatly promoting the development of the IoT industry. In the field of tandem organic solar cells, the front cell based on medium-bandgap acceptors can form a tandem device with the rear cell based on narrow-bandgap acceptors, and the two can achieve complementary absorption, greatly broadening the light absorption range of the device. Tandem organic solar cells are a feasible way to break through the limitation of the intrinsic absorption band (about 200 nm) of organic materials. Making the best use of photons in a larger wavelength range is one of the keys to achieving an improvement in organic photovoltaic efficiency and even rivaling commercial silicon-based solar cells and perovskite solar cells. Therefore, medium-bandgap acceptor materials have important applications in indoor organic photovoltaics and tandem organic solar cells and are the key materials for realizing the development of the IoT and breakthroughs in organic photovoltaic efficiency.

[0005] Since X.W. Zhan et al. reported polycyclic non-fullerene acceptors in 2015, such materials have shown great potential and attracted intense interest from researchers. However, in order to obtain higher photocurrents, researchers have generally been more enthusiastic about designing narrow-bandgap acceptor materials and have overlooked the importance of medium-bandgap acceptors. As a result, medium-bandgap polycyclic non-fullerene acceptor materials are extremely scarce. Through literature research, it was found that there are only a very few reports on medium-bandgap acceptors (Adv. Mater. 2017, 29, 1700254; Chem. Mater. 2019, 31, 3941; Energy Environ. Sci. 2020, 13, 2864; Joule, 2021, 5, 1231; Adv. Mater. 2022, 34, 2108090), and the efficiencies are generally not high. Therefore, in this invention, a class of medium-bandgap acceptors containing a pentacene backbone was designed and synthesized, enabling high-energy-conversion-efficiency indoor photovoltaics and tandem organic solar cell devices. Summary of the Invention

[0006] This invention provides a class of medium-bandgap acceptors containing a pentacene backbone and their preparation methods. The pentacene structure used in such acceptors makes their synthesis simple and easy to modify and regulate. The weakly electron-withdrawing end groups used broaden the bandgap and raise the LUMO by reducing the intramolecular charge transfer effect. Based on the advantages of such acceptors, excellent photovoltaic performance was obtained when they were applied to indoor photovoltaics and tandem organic solar cells.

[0007] The object of the present invention is achieved by the following solution: A class of medium-bandgap acceptors containing a [5,6,6,6]-tetracyclic skeleton and a weak electron-withdrawing end group, and its structural feature is that: using a thiophene unit as a π-bridge, it forms a fused-ring center with a conjugated structure containing a benzene ring, and both sides of the central nucleus are connected to the weak electron-withdrawing end group, and its structural general formula is shown in Formula I:

[0008]

[0009] Weak A is a weak electron-withdrawing end group, and is selected from any one of the following structural formulas:

[0010]

[0011] Wherein, R3-R6 are selected from any one of H, halogen, cyano, C1-C30 alkyl, C1-C30 ester group, C1-C30 alkoxy group, C1-C30 alkylthio group, C1-C30 alkylsilyl group, and C1-C30 alkyl-substituted aryl group; the aryl group in the alkyl-substituted aryl group is a benzene ring or a thiophene ring; the halogen is F, Cl, Br or I;

[0012] Ar is an aromatic group, and is selected from any one of the following structural formulas:

[0013]

[0014] Wherein, Y is selected from any one of O, S, Se or Te; R7, R8 are selected from any one of C1-C30 alkyl, C1-C30 ester group, C1-C30 alkoxy group, C1-C30 alkylthio group, C1-C30 alkylsilyl group or C1-C30 alkyl-substituted aryl group; the aryl group in the alkyl-substituted aryl group is a benzene ring or a thiophene ring;

[0015] R1 is H, halogen, cyano, C1-C50 alkyl, C1-C50 ester group, C1-C50 alkoxy group, C1-C50 alkylthio group, C1-C50 alkylsilyl group or C1-C50 alkyl-substituted aryl group; the aryl group in the alkyl-substituted aryl group is a benzene ring or a thiophene ring; the halogen is F, Cl, Br or I;

[0016] R2 is C1-C50 alkyl, C1-C50 ester group, C1-C50 alkoxy group, C1-C50 alkylthio group, C1-C50 alkylsilyl group or C1-C50 alkyl-substituted aryl group; the aryl group in the alkyl-substituted aryl group is a benzene ring or a thiophene ring;

[0017] X is O, S, Se or Te.

[0018] The optical bandgap of the receptor molecule of the present invention is 1.55 - 2.00 eV, and it mainly absorbs photons in the near-ultraviolet and visible light regions. The pentacene-based structure used in such receptors makes their synthesis simple and easy to modify and regulate. The weakly electron-withdrawing end groups used reduce the intramolecular charge transfer effect, broaden the bandgap, and raise the LUMO. Devices prepared by pairing such receptors with suitable donors can achieve high open-circuit voltages and high energy conversion efficiencies.

[0019] A preparation method of a medium-bandgap receptor material containing a pentacene backbone, characterized by comprising the following steps:

[0020]

[0021] Wherein, Weak A is a weakly electron-withdrawing end group; Ar is an aromatic group; R1 is H, halogen, alkyl, ester group, alkoxy group, alkylthio group, alkylsilyl group or aryl group substituted by alkyl; R2 is alkyl, ester group, alkoxy group, alkylthio group, alkylsilyl group or aryl group substituted by alkyl; X is O, S, Se or Te;

[0022] The specific steps of the above preparation method are as follows:

[0023] (1) Reacting compound A and compound B through a Stille coupling reaction to obtain compound C;

[0024] (2) Subjecting compound C to a Cadogan cyclization reaction to obtain compound D;

[0025] (3) Reacting compound D with a haloalkane through a nucleophilic substitution reaction to obtain compound E;

[0026] (4) Subjecting compound E to a Vilsmeier-Haack formylation reaction to obtain compound F;

[0027] (5) Reacting compound F with a weakly electron-withdrawing end group through a Knoevenagel condensation reaction to obtain compound G, which is a medium-bandgap receptor containing a pentacene backbone.

[0028] The characteristics of the above steps are as follows:

[0029] (1) In the above step (1), the conditions of the Stille coupling reaction are: the solvent is toluene, the catalysts are tris(dibenzylideneacetone)dipalladium and tris(o-tolyl)phosphine, and the addition amounts are 2% - 5% and 10% - 20% of the molar amount of compound B, the molar ratio of compound A to compound B is 3 - 4:1, and the reaction is carried out at 80 - 110 °C for 12 - 15 hours;

[0030] (2) In the step (2), the conditions for the Cadogan cyclization reaction are as follows: the solvent is ortho-dichlorobenzene, the catalyst is triphenylphosphine and the addition amount is 10 times the molar amount of compound C, and the reaction is carried out at 160 - 180 °C for 16 - 18 hours;

[0031] (3) In the step (3), the conditions for the nucleophilic substitution reaction are as follows: the solvent is N,N-dimethylformamide, the catalysts are potassium iodide and cesium carbonate and the addition amounts are both 4 - 5 times the molar amount of compound D, the molar ratio of the haloalkane to compound D is 5 - 6:1, and the reaction is carried out at 80 - 100 °C for 12 - 15 hours;

[0032] (4) In the step (4), the conditions for the Vilsmeier-Haack formylation reaction are as follows: the solvent is 1,2-dichloroethane, the Vilsmeier reagent is N,N-dimethylformamide and phosphorus oxychloride and the addition amounts are both 15 - 20 times the molar amount of compound E, and the reaction is carried out at 80 - 100 °C for 12 - 15 hours;

[0033] (5) In the step (5), the conditions for the Knoevenagel condensation reaction are as follows: the solvent is chloroform, the catalyst is pyridine and the addition amount is 10% - 15% of the volume of chloroform, the molar ratio of compound F to the end group is 5 - 6:1, and the reaction is carried out at 70 - 80 °C for 72 - 96 hours.

[0034] The medium-bandgap acceptor materials in the present invention can obtain excellent photovoltaic performance when applied to indoor organic photovoltaics and tandem organic solar cells.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] (1) The present invention for the first time designed and synthesized a fused-ring non-fullerene acceptor material with a medium bandgap (E g ≈1.55 - 2.00 eV) by synergistically using a pentacene structure and a weak electron-withdrawing end group. Its absorption spectrum is mainly located in the near-ultraviolet and visible light regions, and is significantly blue-shifted compared with common narrow-bandgap acceptor materials.

[0037] (2) The pentacene structure used in such materials not only simplifies the synthesis of the materials, but also enables flexible adjustment of the molecular structure, thus having relatively easily adjustable molecular energy levels and absorption spectra, and can easily meet the requirements of more application environments; the weak electron-withdrawing end groups used in such materials can form close intermolecular packing, which is beneficial to improving the crystallinity of the acceptor molecules and enhancing the intermolecular interaction forces of the acceptor molecules.

[0038] (3) The organic solar cell devices prepared from such materials have a very high open-circuit voltage, and can obtain excellent energy conversion efficiency when matched with the donor PM6, which is superior to other medium-bandgap acceptor materials with the same bandgap.

[0039] (4) The light absorption range of such materials is complementary to that of narrow-bandgap acceptor materials. It can be used as the front cell to match with the narrow-bandgap acceptor-based back cell to achieve good light absorption complementarity, thereby obtaining a tandem organic solar cell with high energy conversion efficiency (efficiency exceeding 20%).

[0040] (5) The light absorption range of such materials highly matches the emission spectrum of indoor light sources. Photovoltaic devices based on such acceptor materials exhibit excellent open-circuit voltage and energy conversion efficiency (efficiency exceeding 26%) under indoor light illumination and have important applications in indoor photovoltaic devices. Description of the Drawings

[0041] Figure 1 It is the thin-film absorption spectrum diagram of the acceptor molecule C8-ThH.

[0042] Figure 2 It is the thin-film absorption spectrum diagram of the acceptor molecule C8-ThCl.

[0043] Figure 3 It is the thin-film absorption spectrum diagram of the acceptor molecule C8-OThCl.

[0044] Figure 4 It is the thin-film absorption spectrum diagram of the acceptor molecule C8-PhCl.

[0045] Figure 5 It is the thin-film absorption spectrum diagram of the acceptor molecule EH-ThCl.

[0046] Figure 6 It is the thin-film absorption spectrum diagram of the acceptor molecule OC8-ThCl.

[0047] Figure 7 It is the thin-film absorption spectrum diagram of the acceptor molecule ThC8-ThCl.

[0048] Figure 8 It is the thin-film absorption spectrum diagram of the acceptor molecule EH-BTA-ThCl.

[0049] Figure 9 It is the thin-film absorption spectrum diagram of the acceptor molecule C8-Qx-ThCl.

[0050] Figure 10 It is the voltage-current density curve diagram of the single-junction cell with C8-ThH, C8-ThCl, and EH-BTA-ThCl as acceptors.

[0051] Figure 11 It is the wavelength-external quantum efficiency diagram of the single-junction cell with C8-ThH, C8-ThCl, and EH-BTA-ThCl as acceptors.

[0052] Figure 12Voltage-current density curves of tandem solar cells with C8-ThH and comparative molecule BTP-CC, BTPT4F-BO, and LBT-DF as the front cell acceptor.

[0053] Figure 13 Voltage-current density curves of single-junction solar cells with C8-ThH and comparative molecule BTP-CC, BTPT4F-BO, and LBT-DF as the acceptor under indoor illumination. Detailed implementation manners

[0054] The following further illustrates the specific implementation of the present invention in conjunction with the drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art.

[0055] The practice of the present invention can adopt the conventional techniques of organic synthetic chemistry within the relevant technical fields. In the following examples, efforts are made to ensure the accuracy of the numbers used (including amounts, temperatures, reaction times, etc.), but some experimental errors and deviations should be considered. The temperatures used in the following examples are expressed in °C, and the pressures are atmospheric pressure or close to atmospheric pressure. The solvents used are all of analytical grade or chromatographic grade. All reactions are carried out in an inert gas atmosphere, and all device preparations are carried out in a glove box under a nitrogen atmosphere. Unless otherwise indicated, all reagents are obtained through commercial channels.

[0056] Example 1

[0057] A medium-bandgap small molecule acceptor C8-ThH containing a pentacene backbone, the structural formula of which is shown as follows:

[0058]

[0059] The synthesis route is as follows:

[0060]

[0061] (1) Synthesis of compound 3

[0062] Under a nitrogen atmosphere, compound 1 (1.46 g, 3 mmol), compound 2 (382 mg, 1 mmol), tris(dibenzylideneacetone)dipalladium (27 mg, 0.03 mmol), and tris(o-tolyl)phosphine (49 mg, 0.16 mmol) were dissolved in 4 mL of toluene. After heating and reacting at 80 °C for 12 h, it was cooled to room temperature and concentrated under reduced pressure to obtain a crude product, and then the crude product was separated and purified by column chromatography to obtain a red solid product (430 mg) with a yield of 70%.

[0063] (2) Synthesis of compound 4

[0064] Under a nitrogen atmosphere, compound 3 (614 mg, 1 mmol) and triphenylphosphine (2.62 g, 10 mmol) were dissolved in 5 mL of ultradry o-dichlorobenzene. After heating the reaction at 180 °C for 17 h, it was cooled to room temperature, and then the crude product in the form of a brown oil was obtained by column chromatography separation and purification, which was directly used for further reaction.

[0065] (3) Synthesis of compound 5

[0066] Under a nitrogen atmosphere, compound 4 (550 mg, 1 mmol), potassium iodide (664 mg, 4 mmol), cesium carbonate (1.30 g, 4 mmol) and 7-bromomethyl-undecane (1.24 g, 5 mmol) were dissolved in 5 mL of ultradry N,N-dimethylformamide. After heating the reaction at 90 °C for 12 h, it was cooled to room temperature, extracted with ethyl acetate, the organic phase was washed with saturated brine and dried with anhydrous magnesium sulfate, and finally the yellowish-brown oily product (443 mg) was obtained by column chromatography separation and purification, with a total two-step yield of 50%.

[0067] (4) Synthesis of compound 6

[0068] Under a nitrogen atmosphere, ultradry phosphorus oxychloride (2.30 g, 15 mmol) and ultradry N,N-dimethylformamide (1.10 g, 15 mmol) were stirred at 0 °C for 30 min, and then compound 5 (887 mg, 1 mmol) dissolved in 6 mL of ultradry 1,2-dichloroethane was added dropwise. After heating the reaction at 90 °C for 12 h, saturated aqueous sodium bicarbonate was added and stirring was continued for 2 h, then it was cooled to room temperature, extracted with dichloromethane, the organic phase was washed with saturated brine and dried with anhydrous magnesium sulfate, and finally the yellow lacquer-like product (641 mg) was obtained by column chromatography separation and purification, with a yield of 68%.

[0069] (5) Synthesis of C8-ThH

[0070] Under a nitrogen atmosphere, compound 6 (471 mg, 0.5 mmol) and compound 7 (500 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of ultradry pyridine was added, and the reaction was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol, and the crude product solid was obtained by filtration. Finally, the blue-black solid product with a metallic luster (399 mg) was obtained by column chromatography separation and purification, with a yield of 61%.

[0071] Figure 1It is the UV-visible absorption spectrum of the compound C8-ThH film. In the range of 300 - 900 nm, the absorption peak of the compound C8-ThH is located at 671 nm, while the optical absorption edge is 725 nm, and the corresponding optical band gap is 1.71 eV.

[0072] Example 2

[0073] A medium-bandgap small molecule acceptor C8-ThCl containing a pentacene skeleton, and its structural formula is shown as follows:

[0074]

[0075] The synthesis route is as follows:

[0076]

[0077] (1) Synthesis of Compound 3 - Compound 6

[0078] The synthesis method of Compound 3 - Compound 6 is the same as that in Example 1.

[0079] (2) Synthesis of C8-ThCl

[0080] Under a nitrogen atmosphere, 6 (471 mg, 0.5 mmol) and 8 (585 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of ultradry pyridine was added, and the mixture was heated and reacted at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol, and the crude product solid was obtained by filtration. Finally, the product was separated and purified by column chromatography to obtain a blue-black solid product with a metallic luster (419 mg), and the yield was 61%.

[0081] Figure 2 It is the UV-visible absorption spectrum of the compound C8-ThCl film. In the range of 300 - 900 nm, the absorption peak of the compound C8-ThCl is located at 703 nm, while the optical absorption edge is 765 nm, and the corresponding optical band gap is 1.62 eV.

[0082] Example 3

[0083] A medium-bandgap small molecule acceptor C8-OThCl containing a pentacene skeleton, and its structural formula is shown as follows:

[0084]

[0085] The synthesis route is as follows:

[0086]

[0087] (1) Synthesis of Compound 3 - Compound 6

[0088] The synthesis methods of Compounds 3 - 6 are the same as those in Example 1.

[0089] (2) Synthesis of C8 - OThCl

[0090] Under a nitrogen atmosphere, Compound 6 (471 mg, 0.5 mmol) and Compound 9 (465 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of ultra - dry pyridine was added, and the mixture was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by suction filtration. Finally, the product was separated and purified by column chromatography to obtain a blue - black solid product with a metallic luster (390 mg), and the yield was 61%.

[0091] Figure 3 is the UV - Vis absorption spectrum of the C8 - OThCl thin film. In the range of 300 - 900 nm, the absorption peak of C8 - OThCl is located at 616 nm, the optical absorption edge is 665 nm, and the corresponding optical band gap is 1.86 eV.

[0092] Example 4

[0093] A medium - band - gap small - molecule acceptor C8 - PhCl containing a [5,5] - fused - ring skeleton, and its structural formula is as follows:

[0094]

[0095] The synthesis route is as follows:

[0096]

[0097] (1) Synthesis of Compounds 3 - 6

[0098] The synthesis methods of Compounds 3 - 6 are the same as those in Example 1.

[0099] (2) Synthesis of C8 - PhCl

[0100] Under a nitrogen atmosphere, Compound 6 (471 mg, 0.5 mmol) and Compound 10 (705 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of ultra - dry pyridine was added, and the mixture was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by suction filtration. Finally, the product was separated and purified by column chromatography to obtain a blue - black solid product with a metallic luster (448 mg), and the yield was 61%.

[0101] Figure 4The UV-visible absorption spectrum of the C8-PhCl compound film shows that in the range of 300 - 900 nm, the absorption peak of the C8-PhCl compound is located at 654 nm, while the optical absorption edge is at 705 nm, and the corresponding optical band gap is 1.76 eV.

[0102] Example 5

[0103] A medium-bandgap small molecule acceptor EH-ThCl containing a pentacene backbone, whose structural formula is as follows:

[0104]

[0105] The synthesis route is as follows:

[0106]

[0107] (1) Synthesis of Compound 12

[0108] Under a nitrogen atmosphere, compound 11 (1.46 g, 3 mmol), compound 2 (382 mg, 1 mmol), tris(dibenzylideneacetone)dipalladium (27 mg, 0.03 mmol), and tris(o-tolyl)phosphine (49 mg, 0.16 mmol) were dissolved in 4 mL of toluene. After heating the reaction at 80 °C for 12 h, it was cooled to room temperature and concentrated under reduced pressure to obtain a crude product. Subsequently, the crude product was separated and purified by column chromatography to obtain a red solid product (430 mg) with a yield of 70%.

[0109] (2) Synthesis of Compound 13

[0110] Under a nitrogen atmosphere, compound 12 (614 mg, 1 mmol) and triphenylphosphine (2.62 g, 10 mmol) were dissolved in 5 mL of ultradry o-dichlorobenzene. After heating the reaction at 180 °C for 17 h, it was cooled to room temperature, and then the crude product was separated and purified by column chromatography to obtain a brown oily crude product, which was directly used for further reaction.

[0111] (3) Synthesis of Compound 14

[0112] Under a nitrogen atmosphere, compound 13 (550 mg, 1 mmol), potassium iodide (664 mg, 4 mmol), cesium carbonate (1.30 g, 4 mmol), and 7-bromomethyl-undecane (1.24 g, 5 mmol) were dissolved in 5 mL of ultradry N,N-dimethylformamide. After heating the reaction at 90 °C for 12 h, it was cooled to room temperature, extracted with ethyl acetate, the organic phase was washed with saturated brine and dried with anhydrous magnesium sulfate, and finally the crude product was separated and purified by column chromatography to obtain a yellow-brown oily product (443 mg) with a two-step total yield of 50%.

[0113] (4) Synthesis of Compound 15

[0114] Under a nitrogen atmosphere, super-dry phosphorus oxychloride (2.30 g, 15 mmol) and super-dry N,N-dimethylformamide (1.10 g, 15 mmol) were stirred at 0 °C for 30 min, and then compound 14 (887 mg, 1 mmol) dissolved in 6 mL of super-dry 1,2-dichloroethane was added dropwise. After heating the reaction at 90 °C for 12 h, saturated aqueous sodium bicarbonate solution was added and stirring was continued for 2 h. Subsequently, it was cooled to room temperature, extracted with dichloromethane, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally purified by column chromatography to obtain a yellow lacquer-like product (641 mg) with a yield of 68%.

[0115] (5) Synthesis of EH-ThCl

[0116] Under a nitrogen atmosphere, compound 15 (471 mg, 0.5 mmol) and compound 8 (585 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of super-dry pyridine was added, and the reaction was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by filtration, and finally purified by column chromatography to obtain a shiny blue-black solid product (419 mg) with a yield of 61%.

[0117] Figure 5 is the UV-visible absorption spectrum of the EH-ThCl compound film. In the range of 300 - 900 nm, the absorption peak of the EH-ThCl compound is located at 716 nm, while the optical absorption edge is 765 nm, and the corresponding optical band gap is 1.62 eV.

[0118] Example 6

[0119] A medium-bandgap small molecule acceptor OC8-ThCl containing a [5,5] bicyclic skeleton, the structural formula of which is shown below:

[0120]

[0121] The synthesis route is as follows:

[0122]

[0123] (1) Synthesis of compound 17

[0124] Under a nitrogen atmosphere, compound 16 (1.51 g, 3 mmol), compound 2 (382 mg, 1 mmol), tris(dibenzylideneacetone)dipalladium (27 mg, 0.03 mmol) and tris(o-tolyl)phosphine (49 mg, 0.16 mmol) were dissolved in 4 mL of toluene. After heating the reaction at 80 °C for 12 h, it was cooled to room temperature and concentrated under reduced pressure to obtain a crude product, which was then separated and purified by column chromatography to obtain a red solid product (452 mg) with a yield of 70%.

[0125] (2) Synthesis of compound 18

[0126] Under a nitrogen atmosphere, compound 17 (646 mg, 1 mmol) and triphenylphosphine (2.62 g, 10 mmol) were dissolved in 5 mL of ultradry o-dichlorobenzene. After heating the reaction at 180 °C for 17 h, it was cooled to room temperature, and then the crude product in the form of a brown oil was separated and purified by column chromatography and directly used for further reaction.

[0127] (3) Synthesis of compound 19

[0128] Under a nitrogen atmosphere, compound 18 (582 mg, 1 mmol), potassium iodide (664 mg, 4 mmol), cesium carbonate (1.30 g, 4 mmol) and 7-bromomethyl-undecane (1.24 g, 5 mmol) were dissolved in 5 mL of ultradry N,N-dimethylformamide. After heating the reaction at 90 °C for 12 h, it was cooled to room temperature, extracted with ethyl acetate, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally the yellowish-brown oily product (459 mg) was separated and purified by column chromatography with a total two-step yield of 50%.

[0129] (4) Synthesis of compound 20

[0130] Under a nitrogen atmosphere, ultradry phosphorus oxychloride (2.30 g, 15 mmol) and ultradry N,N-dimethylformamide (1.10 g, 15 mmol) were stirred at 0 °C for 30 min, and then compound 19 (919 mg, 1 mmol) dissolved in 6 mL of ultradry 1,2-dichloroethane was added dropwise. After heating the reaction at 90 °C for 12 h, saturated sodium bicarbonate aqueous solution was added and stirring was continued for 2 h. Then it was cooled to room temperature, extracted with dichloromethane, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally the yellow lacquer-like product (663 mg) was separated and purified by column chromatography with a yield of 68%.

[0131] (5) Synthesis of OC8-ThCl

[0132] Under a nitrogen atmosphere, compound 20 (487 mg, 0.5 mmol) and compound 8 (585 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of super-dry pyridine was added, and the mixture was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by filtration, and finally, the blue-black solid product with a metallic luster (429 mg) was obtained by column chromatography separation and purification, with a yield of 61%.

[0133] Figure 6 Figure 4 shows the UV-Vis absorption spectrum of the compound OC8-ThCl film. In the range of 300 - 900 nm, the absorption peak of the compound OC8-ThCl is located at 698 nm, while the optical absorption edge is 740 nm, and the corresponding optical band gap is 1.68 eV.

[0134] Example 7

[0135] A medium bandgap small molecule acceptor ThC8-ThCl containing a [5,5] fused-ring skeleton, the structural formula of which is shown as follows:

[0136]

[0137] The synthesis route is as follows:

[0138]

[0139] (1) Synthesis of compound 22

[0140] Under a nitrogen atmosphere, compound 21 (1.70 g, 3 mmol), compound 2 (382 mg, 1 mmol), tris(dibenzylideneacetone)dipalladium (27 mg, 0.03 mmol) and tris(o-tolyl)phosphine (49 mg, 0.16 mmol) were dissolved in 4 mL of toluene. After heating at 80 °C for 12 h, it was cooled to room temperature and concentrated under reduced pressure to obtain a crude product. Subsequently, the red solid product (545 mg) was obtained by column chromatography separation and purification, with a yield of 70%.

[0141] (2) Synthesis of compound 23

[0142] Under a nitrogen atmosphere, compound 22 (778 mg, 1 mmol) and triphenylphosphine (2.62 g, 10 mmol) were dissolved in 5 mL of super-dry o-dichlorobenzene. After heating at 180 °C for 17 h, it was cooled to room temperature, and then the brown oily crude product was obtained by column chromatography separation and purification and directly used for further reaction.

[0143] (3) Synthesis of compound 24

[0144] Under a nitrogen atmosphere, compound 23 (714 mg, 1 mmol), potassium iodide (664 mg, 4 mmol), cesium carbonate (1.30 g, 4 mmol), and 7-bromomethyl-undecane (1.24 g, 5 mmol) were dissolved in 5 mL of ultra-dry N,N-dimethylformamide. After heating the reaction at 90 °C for 12 h, it was cooled to room temperature, extracted with ethyl acetate, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally purified by column chromatography to obtain a yellow-brown oily product (525 mg), with a total yield of 50% for the two steps.

[0145] (4) Synthesis of compound 25

[0146] Under a nitrogen atmosphere, phosphorus oxychloride (2.30 g, 15 mmol) and N,N-dimethylformamide (1.10 g, 15 mmol) were stirred at 0 °C for 30 min, and then compound 24 (1.05 g, 1 mmol) dissolved in 6 mL of ultra-dry 1,2-dichloroethane was added dropwise. After heating the reaction at 90 °C for 12 h, saturated aqueous sodium bicarbonate was added and stirring was continued for 2 h. Subsequently, it was cooled to room temperature, extracted with dichloromethane, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally purified by column chromatography to obtain a yellow lacquer-like product (752 mg), with a yield of 68%.

[0147] (5) Synthesis of ThC8-ThCl

[0148] Under a nitrogen atmosphere, compound 25 (553 mg, 0.5 mmol) and compound 8 (585 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of ultra-dry pyridine was added, and the reaction was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by filtration, and finally purified by column chromatography to obtain a blue-black solid product with a metallic luster (469 mg), with a yield of 61%.

[0149] Figure 7 is the ultraviolet-visible absorption spectrum of the ThC8-ThCl thin film. In the range of 300 - 900 nm, the absorption peak of compound ThC8-ThCl is located at 686 nm, while the optical absorption edge is 750 nm, and the corresponding optical band gap is 1.65 eV.

[0150] Example 8

[0151] A medium-bandgap small molecule acceptor EH-BTA-ThCl containing a [5,5] fused-ring skeleton, and its structural formula is as follows:

[0152]

[0153] The synthetic route is as follows:

[0154]

[0155] (1) Synthesis of Compound 27

[0156] Under a nitrogen atmosphere, compound 11 (1.46 g, 3 mmol), compound 26 (421 mg, 1 mmol), tris(dibenzylideneacetone)dipalladium(0) (27 mg, 0.03 mmol), and tris(o-tolyl)phosphine (49 mg, 0.16 mmol) were dissolved in 4 mL of toluene. After heating the reaction mixture at 80 °C for 12 h, it was cooled to room temperature and concentrated under reduced pressure to obtain a crude product. Subsequently, the crude product was separated and purified by column chromatography to obtain a red solid product (457 mg) with a yield of 70%.

[0157] (2) Synthesis of Compound 28

[0158] Under a nitrogen atmosphere, compound 27 (653 mg, 1 mmol) and triphenylphosphine (2.62 g, 10 mmol) were dissolved in 5 mL of ultradry o-dichlorobenzene. After heating the reaction mixture at 180 °C for 17 h, it was cooled to room temperature. Subsequently, the crude product was separated and purified by column chromatography to obtain a brown oily crude product, which was directly used for further reaction.

[0159] (3) Synthesis of Compound 29

[0160] Under a nitrogen atmosphere, compound 28 (589 mg, 1 mmol), potassium iodide (664 mg, 4 mmol), cesium carbonate (1.30 g, 4 mmol), and 7-bromomethyl-undecane (1.24 g, 5 mmol) were dissolved in 5 mL of ultradry N,N-dimethylformamide. After heating the reaction mixture at 90 °C for 12 h, it was cooled to room temperature, extracted with ethyl acetate, and the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate. Finally, the crude product was separated and purified by column chromatography to obtain a yellowish-brown oily product (463 mg) with an overall two-step yield of 50%.

[0161] (4) Synthesis of Compound 30

[0162] Under a nitrogen atmosphere, ultradry phosphorus oxychloride (2.30 g, 15 mmol) and ultradry N,N-dimethylformamide (1.10 g, 15 mmol) were stirred at 0 °C for 30 min, and then compound 29 (926 mg, 1 mmol) dissolved in 6 mL of ultradry 1,2-dichloroethane was added dropwise. After heating the reaction mixture at 90 °C for 12 h, saturated aqueous sodium bicarbonate was added and stirring was continued for 2 h. Subsequently, it was cooled to room temperature, extracted with dichloromethane, and the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate. Finally, the crude product was separated and purified by column chromatography to obtain a yellowish lacquer-like product (668 mg) with a yield of 68%.

[0163] (5) Synthesis of EH-BTA-ThCl

[0164] Under a nitrogen atmosphere, compound 30 (491 mg, 0.5 mmol) and compound 8 (585 mg, 2.5 mmol) were dissolved in 10 mL of chloroform. 1.5 mL of ultra-dry pyridine was added, and the mixture was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by filtration, and finally, the blue-black solid product with a metallic luster (431 mg) was obtained by column chromatography separation and purification, with a yield of 61%.

[0165] Figure 8 Figure 8 is the UV-Vis absorption spectrum of the EH-BTA-ThCl compound film. In the range of 300 - 900 nm, the absorption peak of the EH-BTA-ThCl compound is located at 714 nm, while the optical absorption edge is 785 nm, and the corresponding optical band gap is 1.58 eV.

[0166] Example 9

[0167] A medium-bandgap small molecule acceptor C8-Qx-ThCl containing a pentacene backbone, and its structural formula is as follows:

[0168]

[0169] The synthesis route is as follows:

[0170]

[0171] (1) Synthesis of compound 32

[0172] Under a nitrogen atmosphere, compound 1 (1.46 g, 3 mmol), compound 31 (404 mg, 1 mmol), tris(dibenzylideneacetone)dipalladium (27 mg, 0.03 mmol), and tris(o-tolyl)phosphine (49 mg, 0.16 mmol) were dissolved in 4 mL of toluene. After heating at 80 °C for 12 h, it was cooled to room temperature and concentrated under reduced pressure to obtain a crude product. Subsequently, the red solid product (445 mg) was obtained by column chromatography separation and purification, with a yield of 70%.

[0173] (2) Synthesis of compound 33

[0174] Under a nitrogen atmosphere, compound 32 (636 mg, 1 mmol) and triphenylphosphine (2.62 g, 10 mmol) were dissolved in 5 mL of ultra-dry o-dichlorobenzene. After heating at 180 °C for 17 h, it was cooled to room temperature, and then the brown oily crude product was obtained by column chromatography separation and purification and directly used for further reaction.

[0175] (3) Synthesis of Compound 34

[0176] Under a nitrogen atmosphere, compound 33 (572 mg, 1 mmol), potassium iodide (664 mg, 4 mmol), cesium carbonate (1.30 g, 4 mmol), and 7-bromomethyl-undecane (1.24 g, 5 mmol) were dissolved in 5 mL of ultradry N,N-dimethylformamide. After heating the reaction at 90 °C for 12 h, it was cooled to room temperature, extracted with ethyl acetate, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally purified by column chromatography to obtain a yellow-brown oily product (454 mg), with a total yield of 50% in two steps.

[0177] (4) Synthesis of Compound 35

[0178] Under a nitrogen atmosphere, ultradry phosphorus oxychloride (2.30 g, 15 mmol) and ultradry N,N-dimethylformamide (1.10 g, 15 mmol) were stirred at 0 °C for 30 min, and then compound 34 (909 mg, 1 mmol) dissolved in 6 mL of ultradry 1,2-dichloroethane was added dropwise. After heating the reaction at 90 °C for 12 h, saturated aqueous sodium bicarbonate was added and stirring was continued for 2 h. Subsequently, it was cooled to room temperature, extracted with dichloromethane, the organic phase was washed with saturated brine and dried over anhydrous magnesium sulfate, and finally purified by column chromatography to obtain a yellow lacquer-like product (656 mg), with a yield of 68%.

[0179] (5) Synthesis of C8-BTA-ThCl

[0180] Under a nitrogen atmosphere, compound 35 (482 mg, 0.5 mmol) and compound 8 (585 mg, 2.5 mmol) were dissolved in 10 mL of chloroform, 1.5 mL of ultradry pyridine was added, and the reaction was heated at 65 °C for 72 h. After cooling to room temperature, the reaction solution was concentrated under reduced pressure and precipitated in 200 mL of anhydrous methanol. The crude product solid was obtained by filtration, and finally purified by column chromatography to obtain a blue-black solid product with a metallic luster (426 mg), with a yield of 61%.

[0181] Figure 9 Fig. is the UV-visible absorption spectrum of the C8-Qx-ThCl compound film. In the range of 300 - 900 nm, the absorption peak of the C8-Qx-ThCl compound is located at 684 nm, while the optical absorption edge is 735 nm, and the corresponding optical band gap is 1.69 eV.

[0182] Example 10

[0183] Taking the small molecule acceptor materials C8-ThH, C8-ThCl, and EH-BTA-ThCl obtained in Example 1, Example 3, and Example 8 as examples, the applications of such medium-bandgap acceptor materials in organic solar cells and indoor photovoltaic devices are illustrated, but the present invention is not limited to the examples given.

[0184] The specific device preparation process is as follows:

[0185] (1) Preparation of single-junction organic solar cell devices

[0186] Spin-coat a 40-nm PEDOT:PSS hole transport layer on ITO, then spin-coat a photoactive layer of about 100 nm of the blend of donor material and acceptor material, then spin-coat about 5 nm of quaternary ammonium bromide of amino polyfluorene (PFN-Br) as the cathode interface layer, and finally evaporate a 100-nm Ag layer to complete the device preparation. Subsequently, the device is tested under a standard solar simulator and an indoor light simulator respectively.

[0187] (2) Preparation of tandem organic solar cell devices

[0188] The tandem device has the following structure: ITO / PEDOT:PSS / front cell active layer / connector layer / rear cell active layer / PDINO / Ag. The preparation process of the front cell active layer is the same as that of the single-junction device. Preparation of the connector layer (ZnO / PEDOT:PSS / PMA): First, spin-coat a ZnO nanoparticle layer (about 20 nm) on the active layer of the front cell, and then spin-coat PEDOT:PSS (diluted with deionized water at a ratio of 1:2.5) on the ZnO layer (about 15 nm). Anneal the substrate at 100 °C for 5 min, and then spin-coat about 5 nm of phosphomolybdic acid (PMA) on the PEDOT:PSS. The preparation method of the rear cell active layer is the same as that of the single-junction device. After the preparation of the front cell, the connector layer, and the rear cell active layer is completed, spin-coat the electron transport layer PDINO (3000 rpm). Finally, deposit the Ag electrode by evaporation under high vacuum to obtain the tandem cell device.

[0189] Figure 10Voltage-current density curves of organic solar cell devices based on PM6:C8-ThH, PM6:C8-ThCl, and PM6:EH-BTA-ThCl. The PM6:C8-ThH device exhibits an open-circuit voltage of 1.11 V, a short-circuit current density of 16.94 mA / cm², and a fill factor of 78.80%, ultimately achieving an energy conversion efficiency of 14.81%. The PM6:C8-ThCl device exhibits an open-circuit voltage of 1.05 V, a short-circuit current density of 18.40 mA / cm², and a fill factor of 73.10%, ultimately achieving an energy conversion efficiency of 14.12%. The PM6:EH-BTA-ThCl device exhibits an open-circuit voltage of 1.07 V, a short-circuit current density of 19.11 mA / cm², and a fill factor of 68.97%, ultimately achieving an energy conversion efficiency of 14.10%.

[0190] Figure 11 Wavelength-external quantum efficiency graphs of organic solar cell devices based on PM6:C8-ThH, PM6:C8-ThCl, and PM6:EH-BTA-ThCl. It can be found that the three devices have good light responses in the spectral range of 300 - 720 nm. Among them, the external quantum efficiencies of the PM6:C8-ThCl and PM6:EH-BTA-ThCl devices exceed 75% in the range of 440 - 660 nm, while the PM6:C8-ThH device has a higher responsiveness in this range, with a responsivity exceeding 80%. Therefore, the three devices exhibit excellent performance.

[0191] Table 1. Device parameter table of single-junction organic solar cells based on PM6 and medium-bandgap acceptors C8-ThH, C8-ThCl, EH-BTA-ThCl under simulated solar illumination (AM1.5G)

[0192]

[0193] Table 2. Device parameter table of tandem organic solar cells based on PM6 and medium-bandgap acceptors C8-ThH, C8-ThCl, EH-BTA-ThCl under simulated solar illumination (AM1.5G)

[0194]

[0195] Table 3. Performance parameter table of tandem devices composed of a front cell based on PM6:C8-ThH and different rear cells under simulated solar illumination (AM1.5G)

[0196]

[0197] Table 4. Device parameters of single-junction organic solar cells based on PM6 and medium-bandgap acceptors C8-ThH, C8-ThCl, and EH-BTA-ThCl under indoor illumination (illuminance of 1000 lux, input power of 284 μW / cm²)

[0198]

[0199] As can be seen from Table 1, single-junction organic solar cells based on PM6 and medium-bandgap acceptors C8-ThH, C8-ThCl, and EH-BTA-ThCl containing a pentacene backbone exhibit an open-circuit voltage exceeding 1.0 V and good energy conversion efficiency, indicating that such materials have great application potential. As can be seen from Table 2, tandem organic solar cells prepared with front cells based on PM6:C8-ThH, PM6:C8-ThCl, and PM6:EH-BTA-ThCl as the active layer and rear cells based on PTTzF:Y6:

[70] PCBM as the active layer all achieved an energy conversion efficiency of about 20%. This is mainly attributed to the complementary absorption that can be formed between the medium-bandgap material and the narrow-bandgap material, and the front cell provides excellent open-circuit voltage and photovoltaic performance. In addition, in order to study the universality of medium-bandgap materials containing a pentacene backbone in tandem cells, the front cell based on PM6:C8-ThH as the active layer was paired with different rear cells, and the device data are shown in Table 3. It can be found that the front cell based on the medium-bandgap acceptor not only matches well with PTTzF:Y6:

[70] PCBM, but also the efficiency of tandem devices paired with PTB7-Th:O6T-4F and PM6:BTP-eC9 reached 19.93% and 21.46% respectively. The above results show that the medium-bandgap acceptor materials in the present invention not only exhibit good energy conversion efficiency in single-junction devices, but also have excellent photovoltaic performance and universality in tandem cell devices, and are a class of highly potential front cell materials. As can be seen from Table 4, single-junction organic solar cells based on PM6 and medium-bandgap acceptors C8-ThH, C8-ThCl, and EH-BTA-ThCl can achieve energy conversion efficiencies of 26.54%, 25.37%, and 26.47% under indoor illumination conditions. This is mainly due to the high degree of matching between the absorption spectrum of the medium-bandgap acceptor and the emission spectrum of the indoor light source, indicating that the medium-bandgap acceptor containing a pentacene backbone has good application prospects in the field of indoor photovoltaics.

[0200] Comparative example

[0201]

[0202] To further clarify the unique advantages of the medium-bandgap acceptors involved in the present invention, taking Example C8-ThH involved in the present invention as an example, representative acceptors with similar structures were selected for comparison (Comparative Examples 1-3). Among them, the BTP-CC molecule has a heptacene ring structure with a weak electron-withdrawing end group (Comparative Example 1); the BTPT4F-BO molecule has a pentacene ring structure with a strong electron-withdrawing end group (Comparative Example 2); and the LBT-DF molecule is a high-performance medium-bandgap acceptor reported in the literature (Comparative Example 3). Under the same conditions, single-junction devices and tandem devices were fabricated using the above four materials as acceptors, and the single-junction devices were tested under simulated sunlight and indoor light environments. The relevant device data are as Figures 12 - 13 shown in Tables 5-7.

[0203] Figure 12 Figure 6 is a voltage-current density curve of tandem cells prepared by using PM6:BTP-CC, PM6:BTPT4F-BO, PM6:LBT-DF, and PM6:C8-ThH as the front cell and PTTzF:Y6:

[70] PCBM as the back cell, respectively. The PM6:BTP-CC device exhibited an open-circuit voltage of 1.89 V, a short-circuit current density of 7.32 mA / cm², and a fill factor of 48.06%, and finally achieved an energy conversion efficiency of 6.65%. The PM6:BTPT4F-BO device exhibited an open-circuit voltage of 1.70 V, a short-circuit current density of 14.32 mA / cm², and a fill factor of 76.30%, and finally achieved an energy conversion efficiency of 18.57%. The PM6:LBT-DF device exhibited an open-circuit voltage of 1.75 V, a short-circuit current density of 13.85 mA / cm², and a fill factor of 78.22%, and finally achieved an energy conversion efficiency of 18.96%. The PM6:C8-ThH device exhibited an open-circuit voltage of 1.94 V, a short-circuit current density of 13.52 mA / cm², and a fill factor of 78.53%, and finally achieved an energy conversion efficiency of 20.65%.

[0204] Figure 13Voltage-current density curves of single-junction organic solar cells based on PM6:BTP-CC, PM6:BTPT4F-BO, PM6:LBT-DF, and PM6:C8-ThH under indoor lighting conditions. The PM6:BTP-CC device exhibits an open-circuit voltage of 0.88 V, a short-circuit current density of 32.61 μA / cm², and a fill factor of 62.24%, resulting in an energy conversion efficiency of 6.38%. The PM6:BTPT4F-BO device exhibits an open-circuit voltage of 0.72 V, a short-circuit current density of 84.53 μA / cm², and a fill factor of 78.53%, resulting in an energy conversion efficiency of 17.07%. The PM6:LBT-DF device exhibits an open-circuit voltage of 0.75 V, a short-circuit current density of 105.40 μA / cm², and a fill factor of 78.82%, resulting in an energy conversion efficiency of 22.25%. The PM6:C8-ThH device exhibits an open-circuit voltage of 0.95 V, a short-circuit current density of 98.48 μA / cm², and a fill factor of 79.42%, resulting in an energy conversion efficiency of 26.54%.

[0205] Table 5. Device parameter table of single-junction organic solar cells based on PM6 and acceptors BTP-CC, BTPT4F-BO, LBT-DF, C8-ThH under simulated solar illumination (AM1.5G)

[0206]

[0207] As can be seen from Table 5, compared with Comparative Example 1, the PM6:C8-ThH device not only has a higher open-circuit voltage, but also has a more significant advantage in fill factor; compared with Comparative Example 2 and Comparative Example 3, because C8-ThH has a higher LUMO, the open-circuit voltage of the PM6:C8-ThH device is significantly improved. Therefore, the device based on PM6:C8-ThH finally exhibits a higher open-circuit voltage, fill factor, and energy conversion efficiency.

[0208] Table 6. Device parameter table of tandem organic solar cells based on PM6 and acceptors BTP-CC, BTPT4F-BO, LBT-DF, C8-ThH under simulated solar illumination (AM1.5G)

[0209]

[0210] The front cells were respectively prepared with C8-ThH and three comparative materials as acceptors, and the device data of the tandem organic solar cell devices obtained by combining with the back cell based on PTTzF:Y6:

[70] PCBM are shown in Table 6. Due to the low fill factor of Comparative Example 1 and the low open-circuit voltage of Comparative Example 2 and Comparative Example 3, the corresponding tandem devices only achieved energy conversion efficiencies of 6.65%, 18.57% and 18.96% respectively. In contrast, the tandem device based on the front cell of PM6:C8-ThH achieved an energy conversion efficiency of 20.60% due to its higher fill factor and open-circuit voltage, which further indicates that the medium-bandgap acceptor containing a [5,6,5,6] fused-ring backbone involved in the present invention is an excellent front-cell material.

[0211] Table 7. Device parameters of single-junction organic solar cells based on PM6 and acceptors BTP-CC, BTPT4F-BO, LBT-DF, C8-ThH under indoor illumination (illuminance of 1000 lux, input power of 284 μW / cm²)

[0212]

[0213] The device performances of the single-junction organic solar cells based on the above four acceptor materials under indoor illumination are shown in Table 7. The results are similar to those under simulated sunlight illumination. The single-junction organic solar cell based on PM6:C8-ThH obtained an energy conversion efficiency (26.54%) higher than that of the comparative examples due to its higher open-circuit voltage and fill factor.

[0214] In summary, the medium-bandgap fused-ring acceptor molecules obtained by synergistically using a weak electron-withdrawing end group and a [5,6,5,6] fused-ring structure have a high absorption coefficient and a relatively high LUMO. Therefore, when such materials are applied in organic solar cells, excellent photovoltaic performance and a relatively high open-circuit voltage can be obtained simultaneously. Moreover, applying such materials to tandem organic solar cells and indoor organic photovoltaics can achieve a breakthrough in energy conversion efficiency.

[0215] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A class of medium-bandgap acceptors containing a [5,5] fused-ring backbone, characterized in that The general structural formula is as shown in Formula I: Weak A is a weak electron-withdrawing end group, selected from any one of the following structural formulas: Among them, R3-R6 are selected from any one of H, halogen, cyano, C1-C30 alkyl, C1-C30 ester group, C1-C30 alkoxy group, C1-C30 alkylthio group, C1-C30 alkylsilyl group or aryl group substituted by C1-C30 alkyl; the aryl group in the aryl group substituted by alkyl is a benzene ring or a thiophene ring; the halogen is F, Cl, Br or I; Ar is an aromatic group, selected from any one of the following structural formulas: Among them, Y is selected from any one of O, S, Se or Te; R7, R8 are selected from any one of C1-C30 alkyl, C1-C30 ester group, C1-C30 alkoxy group, C1-C30 alkylthio group, C1-C30 alkylsilyl group or aryl group substituted by C1-C30 alkyl; the aryl group in the aryl group substituted by alkyl is a benzene ring or a thiophene ring; R1 is H, halogen, cyano, C1-C50 alkyl, C1-C50 ester group, C1-C50 alkoxy group, C1-C50 alkylthio group, C1-C50 alkylsilyl group or aryl group substituted by C1-C50 alkyl; the aryl group in the aryl group substituted by alkyl is a benzene ring or a thiophene ring; the halogen is F, Cl, Br or I; R2 is C1-C50 alkyl, C1-C50 ester group, C1-C50 alkoxy group, C1-C50 alkylthio group, C1-C50 alkylsilyl group or aryl group substituted by C1-C50 alkyl; the aryl group in the aryl group substituted by alkyl is a benzene ring or a thiophene ring; X is O, S, Se or Te.

2. A method for preparing the medium-bandgap small-molecule acceptor material containing a [5,5] fused-ring backbone according to claim 1, characterized in that It includes the following steps: Among them, Weak A is a weak electron-withdrawing end group; Ar is an aromatic group; R1 is H, halogen, alkyl, ester group, alkoxy group, alkylthio group, alkylsilyl group or aryl group substituted by alkyl; R2 is alkyl, ester group, alkoxy group, alkylthio group, alkylsilyl group or aryl group substituted by alkyl; X is O, S, Se or Te.

3. The method for preparing the medium-bandgap small-molecule acceptor material containing a [5,5] fused-ring backbone according to claim 2, characterized in that It includes the following steps: (1) Compound A and compound B are subjected to a Stille coupling reaction to obtain compound C; (2) Compound C is subjected to a Cadogan cyclization reaction to obtain compound D; (3) Compound D and an alkyl halide are subjected to a nucleophilic substitution reaction to obtain compound E; (4) Compound E is subjected to a Vilsmeier-Haack formylation reaction to obtain compound F; (5) Compound F and a compound containing a weak electron-withdrawing end group are subjected to a Knoevenagel condensation reaction to obtain compound G, which is a medium band-gap acceptor containing a [5,6,5,6] fused ring skeleton.

4. The method for preparing the medium-bandgap small-molecule acceptor material containing a [5,5] fused-ring backbone according to claim 3, characterized in that The specific steps are as follows: (1) In the step (1), the conditions for the Stille coupling reaction are: the solvent is toluene, the catalyst is tris(dibenzylideneacetone)dipalladium and tris(o-tolyl)phosphine, and the reaction is carried out at 80-110 °C for 12-15 hours; (2) In the step (2), the conditions for the Cadogan cyclization reaction are: the solvent is o-dichlorobenzene, the catalyst is triphenylphosphine, and the reaction is carried out at 160-180 °C for 16-18 hours; (3) In the step (3), the conditions for the nucleophilic substitution reaction are as follows: the solvent is N,N-dimethylformamide, the catalysts are potassium iodide and cesium carbonate, and the reaction is carried out at 80 - 100 °C for 12 - 15 hours; (4) In the step (4), the conditions for the Vilsmeier-Haack formylation reaction are as follows: the solvent is 1,2-dichloroethane, the Vilsmeier reagent is N,N-dimethylformamide and phosphorus oxychloride, and the reaction is carried out at 80 - 100 °C for 12 - 15 hours; (5) In the step (5), the conditions for the Knoevenagel condensation reaction are as follows: the solvent is chloroform, the catalyst is pyridine, and the reaction is carried out at 70 - 80 °C for 72 - 96 hours.

5. The method for preparing the medium-bandgap small-molecule acceptor material containing a [5,5] fused-ring backbone according to claim 4, characterized in that In the step (1), the addition amounts of tris(dibenzylideneacetone)dipalladium and tris(o-tolyl)phosphine are 2% - 5% and 10% - 20% of the molar amount of compound B respectively; the molar ratio of compound A to compound B is 3 - 4:

1.

6. The method for preparing the medium-bandgap small-molecule acceptor material containing a [5,5] fused-ring backbone according to claim 4, characterized in that In the step (2), the addition amount of triphenylphosphine is 10 times the molar amount of compound C.

7. The preparation method of the medium bandgap small molecule acceptor material containing a fused pentacyclic skeleton according to claim 4, characterized in that, In the step (3), the addition amounts of potassium iodide and cesium carbonate are both 4 - 5 times the molar amount of compound D; the molar ratio of the haloalkane to compound D is 5 - 6:

1.

8. The preparation method of the medium bandgap small molecule acceptor material containing a fused pentacyclic skeleton according to claim 4, characterized in that, In the step (4), the addition amounts of N,N-dimethylformamide and phosphorus oxychloride are both 15 - 20 times the molar amount of compound E.

9. The preparation method of the medium bandgap small molecule acceptor material containing a fused pentacyclic skeleton according to claim 4, characterized in that, In the step (5), the addition amount of pyridine is 10% - 15% of the volume of chloroform, and the molar ratio of compound F to the end group is 5 - 6:

1.

10. The medium bandgap acceptor material containing a fused pentacyclic skeleton described in claim 1 is applied to an organic solar cell device.

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