An ultra-narrow bandgap electron acceptor, active layer, and organic solar cell

Abstract

This invention discloses an ultra-narrow bandgap electron acceptor. By introducing one or two symmetric or asymmetric acceptors at the ends of benzothiadiazole derivatives, the intramolecular charge transfer effect is enhanced, deepening the HOMO energy level for effective matching with deep-level wide-bandgap polymer electron donors. This invention also discloses an active layer prepared by blending electron donors and electron acceptors, which broadens the absorption spectrum of the active layer, facilitating the transport of photogenerated carriers, and the fabrication process is simple. This invention further discloses the application of the ultra-narrow bandgap electron acceptor in organic solar cells. Binary organic solar cells assembled based on symmetric acceptors exhibit high power conversion efficiency (PCE) and high short-circuit current density; the assembled binary semi-transparent organic solar cells achieve high light utilization efficiency (LUE), effectively improving the device performance and application scenarios of the ultra-narrow bandgap electron acceptor.

Description

Technical Field

[0001] This invention relates to the field of organic photovoltaic technology, and more particularly to an ultra-narrow bandgap electron acceptor, an active layer, and an organic solar cell. Background Technology

[0002] Organic solar cells (OSCs) possess diverse application potential due to their lightweight, semi-transparency, and mechanical flexibility. Developing active layer materials with near-infrared absorption capabilities is crucial for improving OSC performance and expanding its applications. In the early days, when fullerene acceptors were dominant, research largely focused on designing donor materials with near-infrared absorption. With the rise of non-fullerene acceptors, such as the acceptor-donor-acceptor (ADA) type fused-ring acceptors IEIC or ITIC and the A-DA'DA type ladder-shaped fused-ring acceptor Y6, the absorption spectra of acceptor materials have been effectively expanded. This has significantly improved the utilization of the solar spectrum and the generation of photocurrent in OSCs, leading to a rapid increase in power conversion efficiency (PCE) in recent years. Simultaneously, some electron acceptor materials with ultra-narrow bandgap (less than 1.3 eV) have emerged. These ultra-narrow bandgap electron acceptor materials have broad application prospects and scientific value in semi-transparent organic photovoltaics, tandem organic photovoltaics, and organic photodetectors.

[0003] To construct an ultranarrow bandgap electron acceptor with near-infrared absorption, the most effective strategy is to enhance the intramolecular charge transfer effect, that is, to enhance the electron-donating ability of the electron-donating unit (D unit) or the electron-withdrawing ability of the electron-withdrawing unit (A unit). Reference 1 (Jianhui Hou, Huifeng Yao. Design, Synthesis, and Photovoltaic Characterization of a Small Molecular Acceptor with an Ultra-Narrow Band Gap. Angew. Chem. Int. Ed. 56, 3045-3049, 2017, doi: 10.1002 / anie.201610944) discloses an ADA-type ultra-narrow bandgap acceptor IEICO-4F developed by introducing alkoxy side chains into the D unit and fluorine atoms into the A unit on the basic structure of ADA-type fused ring acceptor IEIC. It achieves an absorption band edge of nearly 1000 nm (optical bandgap of 1.24 eV), but the PCE of the binary OSC is only 10.0%, which lags behind the top PCE in the OSC field.

[0004] Reference 2 (Xiaozhang Zhu, Wuyue Liu, Theory-Guided Material Design Enabling High-Performance Multifunctional Semitransparent Organic Photovoltaics without Optical Modulations, Adv. Mater, 34, 2200337, 2022, doi: 10.1002 / adma.202200337) discloses an A-DA'DA type ultranarrow bandgap electron acceptor ATT-9, which is achieved by inserting a quinone-effect π-bridge between the central core and the end of the electron acceptor. Its absorption band edge is 1075 nm, the optical bandgap is 1.15 eV, and the PCE of the binary OSC is only 13.4%, which is inferior to the leading PCE in the OSC field.

[0005] Ultra-narrow bandgap electron acceptors obtained by enhancing the electron-donating ability of D units usually have high HOMO energy levels. This makes it difficult to match them with commonly used high-performance wide bandgap polymer donors (such as PM6, D18, etc.). Furthermore, their resistance to photo-oxidation and intrinsic stability are relatively poor, and their device performance lags far behind the best efficiency in the binary OSC field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an ultra-narrow bandgap electron acceptor. By enhancing the electron-withdrawing ability of the electron acceptor, an ultra-narrow bandgap electron acceptor can be constructed, which can match the energy levels of wide bandgap polymer electron donors and improve resistance to photo-oxidation.

[0007] An ultranarrow bandgap electron acceptor comprises a symmetrical acceptor with a benzothiadiazole-based ladder-shaped fused ring structure as its core and benzothiadiazole derivatives at both ends, as shown in the following structural formula:

[0008]

[0009] Where R1 is C4-C 30 Branched or straight-chain alkyl chains, R2 is C4-C 30 Branched or straight-chain alkyl / alkoxy chains;

[0010] Alternatively, an ultranarrow bandgap electron acceptor comprising an asymmetric acceptor with a benzothiadiazole-based ladder-shaped fused ring structure as its core, one end being a benzothiadiazole derivative terminus, and the other end being a cyanoindanone-based terminus, as shown in the following structural formula:

[0011]

[0012] Where R1 is C4-C30 Branched or straight-chain alkyl chains, R2 is C4-C 30 Branched or straight-chain alkyl / alkoxy chains.

[0013] Preferably, the terminal A of the cyanoindanone is at least one of the following chemical structural formulas:

[0014]

[0015] Both benzothiadiazole derivatives and cyanoindanone derivatives possess strong electron-withdrawing capabilities at their ends, significantly enhancing intramolecular charge transfer effects and thus expanding the absorption of molecules in the near-infrared region.

[0016] This invention develops an end with a super strong electron-withdrawing ability and constructs an ultra-narrow bandgap electron acceptor, which can improve the photoelectric conversion efficiency and stability of the device and improve the application scenarios of the device.

[0017] To address the problem of poor intrinsic stability of electron acceptors, this invention also provides an active layer.

[0018] An active layer comprising a film formed by blending an electron acceptor and an electron donor, wherein the electron donor is a wide-bandgap polymer donor material, and the wide-bandgap polymer donor material is at least one of the following chemical structural formulas:

[0019]

[0020] The electron acceptor is the ultranarrow bandgap electron acceptor described in this invention.

[0021] This invention uses a wide bandgap polymer donor material matched with an ultranarrow bandgap electron acceptor to achieve full coverage of the absorption spectrum of the active layer from the visible region to the near-infrared region.

[0022] Preferably, the weight ratio of electron donor to electron acceptor in the active layer is 1:2 to 2:1, and the thickness of the active layer is 50 to 300 nm.

[0023] The ratio of electron donors to electron acceptors in the active layer affects the crystallinity of the active layer, and thus the blend morphology of the active layer. By adjusting the ratio of electron donors to electron acceptors and the thickness of the active layer within a certain range, the active layer can have better crystallinity, the absorption intensity in different regions can be controlled, the morphology of the blend film can be optimized, and the energy conversion efficiency of organic solar cells can be improved.

[0024] The present invention also provides a method for preparing the active layer, which involves forming a film from a mixed solution of electron acceptor, electron donor and additive, and then annealing the film.

[0025] Preferably, the additive used in the film-forming process is 1,8-diiodooctane or chloronaphthalene, and the volume of the additive is 0.1 to 5% of the volume of the mixed solution of electron acceptor and electron donor.

[0026] Additives are used to induce crystallization of the acceptor material, so that the active layer has a better degree of crystallinity.

[0027] Preferably, the annealing temperature during the annealing process is 80–200°C, and the annealing time is 5–30 min.

[0028] Appropriate annealing of the active layer can improve its crystallinity, which is beneficial for the transport of photogenerated carriers and enhances the generation of photocurrent in the device.

[0029] The present invention also provides an organic solar cell, comprising a substrate, an anode, an anode modification layer, an active layer, a cathode modification layer, and a cathode.

[0030] Preferably, glass is used as the substrate; ITO or FTO is used as the anode; 2PACz, PEDOT:PSS or MoO3 is used as the anode modification layer; PDINN, PFN-Br or ZnO is used as the cathode modification layer; and Ag is used as the cathode.

[0031] This invention selects substrates and electrodes with high transmittance and good conductivity to improve the energy conversion efficiency of the device and reduce the resistivity of the solar cell. In addition, by introducing an interface modification layer between the active layer and the electrode, it can adjust the energy level arrangement between the acceptor and the electrode, form a single carrier transport layer, modify the interface morphology, and regulate the electric field inside the device.

[0032] Preferably, PM6 or D18 is used as the electron donor; BTC-1, BTC-2, or BTC-3 is used as the electron acceptor, and the specific chemical structural formula of the electron acceptor is as follows:

[0033]

[0034] The present invention selects an active layer formed by blending electron donor PM6 or D18 with electron acceptor BTC-1, BTC-2 or BTC-3, respectively, which can solve the problems of poor energy level matching and stability.

[0035] Preferably, the thickness of the cathode Ag is 10 nm to 100 nm, and an optical layer TeO2 is modified on the cathode Ag.

[0036] This invention reduces the cathode thickness of organic solar cells and modifies the optical layer with TeO2, which can be assembled into a semi-transparent organic solar cell, improving the light transmittance and light utilization of the device while maintaining high energy conversion efficiency.

[0037] The beneficial effects of this invention are as follows:

[0038] (1) This invention enhances the intramolecular charge transfer effect and expands the absorption of the electron acceptor in the near-infrared region by introducing one or two benzothiadiazole derivatives at the end. Among them, the symmetric acceptor BTC-2 obtained by introducing two benzothiadiazole derivatives at the end has a significantly extended absorption band edge to about 1000 nm, with a corresponding optical band gap of 1.24 eV, and also has a deep HOMO energy level.

[0039] (2) The preparation method of the active layer provided by the present invention is simple and time-saving.

[0040] (3) The present invention broadens the range of absorption spectrum by forming an active layer through the blending of electron donor and electron acceptor, which is beneficial to the transport of photogenerated carriers.

[0041] (4) The binary organic solar cell PM6:BTC-2 assembled based on electron donor PM6 and electron acceptor BTC-2 has high power conversion efficiency (PCE) and high short-circuit current density, achieving the highest PCE and the highest short-circuit current density of binary organic solar cell devices based on ultra-narrow bandgap electron acceptors.

[0042] (5) The binary semi-transparent organic solar cell PM6:BTC-2, assembled based on electron donor PM6 and electron acceptor BTC-2, has high PCE, high average light transmittance (APT) and high light utilization efficiency (LUE), achieving the highest LUE of binary semi-transparent organic solar cell devices to date. Attached Figure Description

[0043] Figure 1 This is a synthetic route based on the electron acceptors BTC-1, BTC-2, and BTC-3 at the end of benzothiadiazole derivatives.

[0044] Figure 2 These are the chemical structural formulas of BTC-1, BTC-2, and BTC-3.

[0045] Figure 3 These are the cyclic voltammetry test curves for BTC-1, BTC-2, and BTC-3.

[0046] Figure 4 These are the UV-Vis absorption spectra of BTC-1, BTC-2, and BTC-3 in thin film form.

[0047] Figure 5 This is the current-voltage curve of a binary organic solar cell under illumination.

[0048] Figure 6The current-voltage curve of a binary semi-transparent organic solar cell under illumination is obtained by adjusting the Ag electrode and optical layer.

[0049] Figure 7 The current-voltage curve of a binary semi-transparent organic solar cell under illumination is obtained by adjusting the electron acceptor ratio. Detailed Implementation

[0050] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art.

[0051] Example 1

[0052] The polymer electron donor PM6 involved in this invention is a commercially available product, readily available from the manufacturer (Manufacturer: Shuolun Organic Optoelectronics Technology (Beijing) Co., Ltd.; CAS No. (PM6): 1802013-83-7). The benzothiadiazole derivative terminus is a novel material developed in this invention. By connecting the benzothiadiazole-based ladder-shaped fused ring core and terminus through a one-step or two-step Knoevenagel reaction, symmetric or asymmetric electron acceptors based on the benzothiadiazole derivative terminus can be obtained.

[0053] Below are three specific methods for preparing electron acceptors based on the terminal of benzothiadiazole derivatives: BTC-1, BTC-2, and BTC-3. The specific synthetic routes are as follows: Figure 1 As shown (among which, compounds 1, 7, 9, and 10 are commercially available products, all purchased from manufacturers. Compound 1 was purchased from Shanghai Bid Pharmaceutical Technology Co., Ltd.; CAS No.: 129365-93-1; Compound 7 was purchased from Shenzhen Ruixun Optoelectronic Materials Technology Co., Ltd.; catalog number: TPB76; Compound 9 was purchased from Shenzhen Ruixun Optoelectronic Materials Technology Co., Ltd., corresponding CAS No.: 2197167-50-1; Compound 10 was purchased from Shenzhen Ruixun Optoelectronic Materials Technology Co., Ltd., corresponding CAS No.: 2083617-82-5).

[0054] The specific steps for synthesizing BTC-1, BTC-2, and BTC-3 are as follows:

[0055] (1) Synthesis of compound 2

[0056] Compound 1 (5.0 g, 31.6 mmol), dichloromethane (30 mL), and triethylamine (30 mL) were added to a round-bottom flask. SOCl2 (25 mL, 344 mmol) and CH2Cl2 (25 mL) were slowly added dropwise under an ice-water bath to form a mixed solution. The solution was stirred at 50 °C for 5 hours, then a saturated Na2CO3 aqueous solution was added and stirred for 15 minutes. The mixture was filtered, and the filtrate was extracted with dichloromethane. After removing the solvent, the solution was purified by column chromatography (eluent: petroleum ether:dichloromethane = 1:4, v / v) to give a pale yellow solid (4.73 g, yield 80.4%), which was compound 2.

[0057] The molecular structure of compound 2 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 2 was dissolved in deuterated chloroform (CDCl3) and packed into an NMR tube for testing. The results are as follows:

[0058] 1 H NMR (400MHz, CDCl3): δ=8.61 (s, 2H);

[0059] 13 C NMR (400MHz, CDCl3): δ=154.12, 129.97, 114.80, 114.11;

[0060] The nuclear magnetic resonance results indicate the successful synthesis of compound 2.

[0061] (2) Synthesis of compound 3

[0062] Compound 2 (2.4 g, 12.9 mmol) obtained in step (1), acetic acid (30 mL), water (20 mL), and concentrated hydrochloric acid (30 mL, 37% HCl, 363 mmol) were added to a round-bottom flask to form a mixed solution. The mixed solution was stirred at 130 °C for 32 h. After removing the solvent, acetone was added to dissolve the product. The solution was filtered and the filtrate was collected. After removing the solvent, the solution was dried to obtain a pale yellow solid (2.19 g, yield 75.8%), which was compound 3.

[0063] The molecular structure of compound 3 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 3 was dissolved in deuterated dimethyl sulfoxide (DMSO-d6), packed into an NMR tube, and tested. The results are as follows:

[0064] 1H NMR (400MHz, DMSO-d6): δ=13.55 (s, 2H), 8.40 (s, 2H);

[0065] 13C NMR (400MHz, DMSO-d6): δ=167.74, 153.89, 133.88, 121.99;

[0066] The nuclear magnetic resonance results indicate the successful synthesis of compound 3.

[0067] (3) Synthesis of compound 4

[0068] Compound 3 (3.5 g, 15.6 mmol) obtained in step (2), anhydrous toluene (50 mL), and trifluoroacetic anhydride (15 mL, 108 mmol) were added to a round-bottom flask to form a mixed solution. The mixed solution was stirred at 40 °C for 10 h. After cooling, water was slowly added dropwise and stirred for 15 min. The crude product was extracted with dichloromethane, and after removing the solvent, it was dried to obtain a pale yellow solid (1.82 g, yield 56.5%), which was compound 4.

[0069] The molecular structure of compound 4 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 4 was dissolved in deuterated dimethyl sulfoxide (DMSO-d6), packed into an NMR tube, and tested. The results are as follows:

[0070] 1 H NMR (400MHz, DMSO-d6): δ = 8.95 (s, 2H);

[0071] 13 C NMR (400MHz, DMSO-d6): δ=162.42, 156.36, 130.19, 120.51;

[0072] The nuclear magnetic resonance results indicate the successful synthesis of compound 4.

[0073] (4) Synthesis of compound 5

[0074] Step 1: Add compound 4 (1.0 g, 4.85 mmol) and 1,4-dioxane (60 mL) to a round-bottom flask. Add ethyl (triphenylphosphine) acetate (1.86 g, 5.34 mmol) in portions over 30 min to form a mixed solution. Stir the mixture at 85 °C for 6 h. After removing the solvent, dry to obtain a light brown solid, which is compound 4-1.

[0075] The molecular structure of compound 4-1 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 4-1 was dissolved in deuterated chloroform (CDCl3) and packed into an NMR tube for testing. The results are as follows:

[0076] 1 H NMR (400MHz, CDCl3): δ=9.91 (s, 1H), 8.68 (s, 1H), 6.28 (s, 1H), 4.35 (q, J=7.2Hz, 2H), 1.39 (t, J=7.1Hz, 3H);

[0077] The nuclear magnetic resonance results indicate the successful synthesis of compound 4-1.

[0078] Step 2: Add compound 4-1, methanol (20 mL), and a methanol solution of sodium methoxide (1.08 mL, 5.4 M, 5.8 mmol) to a round-bottom flask to form a mixed solution. Stir the mixed solution at 65 °C for 5 h. Filter the solution, wash the filter cake with methanol, and dry it to obtain a yellow solid, which is compound 4-2.

[0079] Step 3: Add compound 4-2, acetonitrile (30 mL), and concentrated hydrochloric acid (0.4 mL, 37% HCl, 4.84 mmol) to a round-bottom flask to form a mixed solution. Stir the mixed solution at room temperature for 0.5 h. Filter under vacuum, wash the filter cake with acetonitrile, and air dry to obtain a pale yellow solid, which is compound 4-3.

[0080] The molecular structure of compound 4-3 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 4-3 was dissolved in deuterated dimethyl sulfoxide (DMSO-d6), packed into an NMR tube, and tested. The results are as follows:

[0081] 1 H NMR (400MHz, DMSO-d6): δ=9.83 (s, 1H), 7.92 (s, 2H), 4.13 (q, J=7.1Hz, 2H), 1.23 (t, J=7.1Hz, 3H);

[0082] The nuclear magnetic resonance results indicate the successful synthesis of compound 4-3.

[0083] Step 4: Add compound 4-3 and anhydrous acetonitrile (80 mL) to a round-bottom flask to form a mixed solution. Stir the mixed solution at 90 °C for 20 h. Filter and collect the filtrate. After removing the solvent, wash the filter cake with isopropanol and dry it to obtain a reddish-brown solid (0.55 g, yield 55.5%), which is compound 5.

[0084] The molecular structure of compound 5 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 5 was dissolved in deuterated chloroform (CDCl3), packed into an NMR tube, and tested. The results are as follows:

[0085] 1 H NMR (400MHz, CDCl3): δ=8.67 (s, 2H), 3.49 (s, 2H);

[0086] 13 C NMR (400MHz, CDCl3): δ=196.28, 157.45, 140.86, 117.84, 47.64;

[0087] The nuclear magnetic resonance results indicate the successful synthesis of compound 5.

[0088] (5) Synthesis of compound 6

[0089] Compound 5 (50 mg, 0.245 mmol), malononitrile (32.4 mg, 0.490 mmol), chlorobenzene (10 mL), pyridine (0.3 mL), and titanium tetrachloride (0.3 mL) were added to a round-bottom flask to form a mixed solution. The mixture was stirred at 50 °C for 6 h. After cooling, the solution was poured into water, and the crude product was extracted with chloroform. After removing the solvent, the crude product was dissolved in an appropriate amount of chloroform, precipitated with petroleum ether, filtered, and the process was repeated twice. The filter cake was dried to give a brown solid (15 mg, yield 24.3%), which was compound 6.

[0090] The molecular structure of compound 6 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 6 was dissolved in deuterated chloroform (CDCl3) and packed into an NMR tube for testing. The results are as follows:

[0091] 1 H NMR (400MHz, CDCl3): δ=9.42 (s, 1H), 8.65 (s, 1H), 3.96 (s, 2H);

[0092] The molecular structure of compound 6 was determined using quadrupole time-of-flight (QTOF) mass spectrometry (MS). Specifically, compound 6 was dissolved in chloroform as a dilute solution, and a suitable amount was deposited onto the stage. After the solvent was dried, the solution was tested. The results are as follows:

[0093] MS(Q TOF): Cald for C 12 H4N4OS(M + ): 252.25, Found: 251.00;

[0094] Nuclear magnetic resonance and mass spectrometry results indicate the successful synthesis of compound 6.

[0095] (6) Synthesis of compound 8

[0096] Compound 7 (93 mg, 0.080 mmol), compound 6 (20 mg, 0.079 mmol), chloroform (20 mL), acetic anhydride (0.8 mL), and boron trifluoride diethyl ether (0.4 mL) were added to a two-necked round-bottom flask to form a mixed solution. The mixture was stirred at 60 °C for 3 h. After cooling, methanol was slowly added and stirred for 15 min. The mixture was filtered, the filter cake was washed with methanol, and purified by column chromatography (eluent: petroleum ether: dichloromethane = 1:1, v / v) to obtain a green solid (46 mg, 41.2%), which was compound 8.

[0097] The molecular structure of compound 8 was determined using nuclear magnetic resonance spectroscopy. Specifically, compound 8 was dissolved in deuterated chloroform (CDCl3), packed into an NMR tube, and tested. The results are as follows:

[0098] 1 H NMR (400MHz, CDCl3): δ=10.14 (s, 1H), 9.39 (s, 1H), 9.28 (s, 1H), 8.49 (s, 1H), 4.71 (dd, J=36.8, 7.9Hz, 4H), 3.18(dd, J=43.0, 7.5Hz, 4H), 2.14-2.04(m, 4H), 1.43-1.36(m, 8H), 1.31-0.82(m, 68H), 0.69-0.62(m, 12H);

[0099] The nuclear magnetic resonance results indicate the successful synthesis of compound 8.

[0100] (7) Synthesis of BTC-1

[0101] Compound 8 (50 mg, 0.036 mmol), compound 9 (11 mg, 0.042 mmol), anhydrous toluene (20 mL), acetic anhydride (0.8 mL), and boron trifluoride diethyl ether (0.4 mL) were added to a two-necked round-bottom flask to form a mixed solution. The mixture was stirred at 60 °C for 2 h. After cooling, methanol was slowly added and stirred for 15 min. The mixture was filtered, the filter cake was washed with methanol, and purified by column chromatography (eluent: petroleum ether: dichloromethane = 1:3, v / v) to give a black solid (49 mg, 83.4%), which was compound BTC-1.

[0102] The molecular structure of compound BTC-1 was determined using nuclear magnetic resonance spectroscopy. Specifically, BTC-1 was dissolved in deuterated chloroform (CDCl3) and packed into an NMR tube for testing. The results are as follows:

[0103] 1 H NMR (400MHz, CDCl3): δ=9.40 (s, 1H), 9.29 (s, 1H), 9.17 (s, 1H), 8.80 (s, 1H), 8.50 (s, 1H), 7.96 (s, 1H), 4.78 (t, J=7.7Hz, 4H), 3 .21(dd, J=18.4, 7.7Hz, 4H), 2.17-2.07(m, 4H), 1.52-1.44(m, 4H), 1.40-1.36(m, 4H), 1.28-0.82(m, 68H), 0.71-0.64(m, 12H);

[0104] The molecular structure of compound BTC-1 was determined using matrix-assisted laser desorption / ionization time-of-flight (MALDI) mass spectrometry (MS). Specifically, BTC-1 was dissolved in dilute chloroform, and a suitable amount was deposited onto the stage. After the solvent was dried, the structure was analyzed. The results are as follows:

[0105] MS (MALDI TOF): Cald for C 92 H 106 C 12 N 10 O2S6(M + ): 1647.19, Found: 1647.07;

[0106] Nuclear magnetic resonance and mass spectrometry results indicate the successful synthesis of compound BTC-1, such as Figure 2 As shown in BTC-1.

[0107] (8) Synthesis of BTC-2

[0108] Compound 7 (107 mg, 0.092 mmol), compound 6 (58 mg, 0.230 mmol), chloroform (30 mL), acetic anhydride (1.6 mL), and boron trifluoride diethyl ether (0.8 mL) were added to a two-necked round-bottom flask to form a mixed solution. The mixture was stirred at 60 °C for 10 h. After cooling, methanol was slowly added and stirred for 15 min. The mixture was filtered, the filter cake was washed with methanol, and purified by column chromatography (eluent: petroleum ether: dichloromethane = 1:4, v / v) to give a black solid (47 mg, 31.3%), which was compound BTC-2.

[0109] The molecular structure of compound BTC-2 was determined using nuclear magnetic resonance spectroscopy. Specifically, BTC-2 was dissolved in deuterated chloroform (CDCl3) and packed into an NMR tube for testing. The results are as follows:

[0110] 1 H NMR (400MHz, CDCl3): δ=9.41 (s, 2H), 9.30 (s, 2H), 8.51 (s, 2H), 4.81 (d, J=7.3Hz, 4H), 3.23 (d, J=7.6Hz , 4H), 2.17-2.09(m, 4H), 1.53-1.47(m, 4H), 1.42-1.39(m, 4H), 1.25-0.83(m, 68H), 0.72-0.66(m, 12H);

[0111] The molecular structure of compound BTC-2 was determined using matrix-assisted laser desorption / ionization time-of-flight (MALDI) mass spectrometry (MS). Specifically, BTC-2 was dissolved in dilute chloroform, and a suitable amount was deposited onto the stage. After the solvent was dried, the structure was analyzed. The results are as follows:

[0112] MS (MALDI TOF): Cald for C 92 H 106 N 12 O2S7(M + ): 1636.36, Found: 1636.14;

[0113] Nuclear magnetic resonance and mass spectrometry results indicate the successful synthesis of compound BTC-2, such as Figure 2 As shown in BTC-2.

[0114] (9) Synthesis of BTC-3

[0115] Compound 8 (50 mg, 0.036 mmol), compound 10 (10 mg, 0.043 mmol), anhydrous toluene (20 mL), acetic anhydride (0.8 mL), and boron trifluoride diethyl ether (0.4 mL) were added to a two-necked round-bottom flask to form a mixed solution. The mixture was stirred at 60 °C for 2 h. After cooling, methanol was slowly added and stirred for 15 min. The mixture was filtered, the filter cake was washed with methanol, and purified by column chromatography (eluent: petroleum ether:dichloromethane = 1:2, v / v) to give a black solid (48 mg, 83.4%), which was compound BTC-3.

[0116] The molecular structure of compound BTC-3 was determined using nuclear magnetic resonance spectroscopy. Specifically, BTC-3 was dissolved in deuterated chloroform (CDCl3) and packed into an NMR tube for testing. The results are as follows:

[0117] 1 H NMR (400MHz, CDCl3): δ=9.39 (s, 1H), 9.28 (s, 1H), 9.16 (s, 1H), 8.57 (dd, J=9.9, 6.4Hz, 1H), 8.50 (s, 1H), 7.70 (t, J=7.5Hz, 1H), 4.78 (t, J= 7.9Hz, 4H), 3.20 (dd, J=12.4, 7.6Hz, 4H), 2.16-2.06 (m, 4H), 1.53-1.44 (m, 4H), 1.39-1.37 (m, 4H), 1.28-0.82 (m, 68H), 0.70-0.65 (m, 12H);

[0118] The molecular structure of compound BTC-3 was determined using matrix-assisted laser desorption / ionization time-of-flight (MALDI) mass spectrometry (MS). Specifically, BTC-3 was dissolved in chloroform as a dilute solution, and a suitable amount was deposited onto the stage. After the solvent was dried, the structure was analyzed. The results are as follows:

[0119] MS (MALDI TOF): Cald for C 92 H 106 F2N 10 O2S6(M + ): 1614.28, Found: 1613.97;

[0120] Nuclear magnetic resonance and mass spectrometry results indicate the successful synthesis of compound BTC-3, such as Figure 2 As shown in BTC-3.

[0121] Figure 3 These are the cyclic voltammetry curves for BTC-1, BTC-2, and BTC-3. The results show that, measured by cyclic voltammetry (CV), the LUMO level of BTC-1 is -3.97 eV, the HOMO level is -5.78 eV, and the corresponding electrochemical band gap is 1.81 eV; the LUMO level of BTC-2 is -4.03 eV, the HOMO level is -5.81 eV, and the corresponding electrochemical band gap is 1.78 eV; and the LUMO level of BTC-3 is -3.98 eV, the HOMO level is -5.76 eV, and the corresponding electrochemical band gap is 1.78 eV.

[0122] Figure 4 These are the UV-Vis absorption spectra of BTC-1, BTC-2, and BTC-3. The results show that, measured by absorption spectroscopy in the thin film state, the maximum absorption peak of BTC-1 is located at 869 nm, with an absorption band edge of 950 nm and an optical band gap of 1.31 eV; the maximum absorption peak of BTC-2 is located at 900 nm, with an absorption band edge of 1000 nm and an optical band gap of 1.24 eV; and the maximum absorption peak of BTC-3 is located at 858 nm, with an absorption band edge of 960 nm and an optical band gap of 1.29 eV.

[0123] Example 2

[0124] The assembly of organic solar cells based on the synthesized electron acceptor BTC-1 includes the following steps:

[0125] (1) Anode: The transparent conductive glass with strip-shaped ITO (anode) etched on the surface is cleaned by ultrasonic vibration with cleaning agent, deionized water, acetone and isopropanol in sequence, dried, and then treated with ultraviolet ozone for 10 minutes.

[0126] (2) Anode modification layer: A 2PACz transport layer was spin-coated onto the surface of the conductive glass with a 0.22 mg / mL 2PACz methanol solution, and then annealed at 100°C for 10 minutes.

[0127] (3) Active layer: Before spin-coating the active layer, a PM6:BTC-1 chloroform solution with an electron donor-to-acceptor mass ratio of 1:1.2 and a total concentration of 16 mg / mL was prepared, and 0.25% of 1,8-diiodooctane (DIO) was added as an additive. After stirring and dissolving at 60°C for 1 hour, the solution was spin-coated at 4000 rpm to obtain an active layer of approximately 100 nm. Then, the solution was annealed at 90°C for 5 minutes.

[0128] (4) Cathode modification layer: On the active layer prepared in step (3), a PDINN transport layer is spin-coated with a 1.5 mg / mL PDINN methanol solution.

[0129] (5) Cathode: Based on step (4), a 100nm Ag electrode is deposited using a vapor deposition apparatus to obtain an effective area of ​​6mm². 2 The organic solar cell, designated PM6:BTC-1, has a tested area of ​​4.572 mm². 2 .

[0130] At a light intensity of 100mW / cm 2 Under AM1.5 simulated sunlight irradiation, the current-voltage curves of the PM6:BTC-1 device were tested, and the results are as follows: Figure 5 As shown in the figure. The results show that the open-circuit voltage of the PM6:BTC-1 device is 0.765V, and the short-circuit current density is 25.51mA / cm². 2 The fill factor is 73.35%, and the power conversion efficiency (PCE) is 14.33%.

[0131] Comparative Example 1

[0132] Organic solar cells were assembled based on the synthesized electron acceptor BTC-2, with the specific steps being the same as in Example 2, except that BTC-2 was selected as the electron acceptor to assemble a PM6:BTC-2 device.

[0133] At a light intensity of 100mW / cm 2 Under AM1.5 simulated sunlight irradiation, the current-voltage curves of the PM6:BTC-2 device were tested, and the results are as follows: Figure 5 As shown in the figure. The results show that the open-circuit voltage of the PM6:BTC-2 device is 0.722V, and the short-circuit current density is 30.34mA / cm². 2 The fill factor is 78.39%, and the power conversion efficiency (PCE) is 17.17%.

[0134] Comparative Example 2

[0135] Organic solar cells were assembled based on the synthesized electron acceptor BTC-3, with the specific steps being the same as in Example 2, except that BTC-3 was selected as the electron acceptor to assemble a PM6:BTC-3 device.

[0136] At a light intensity of 100mW / cm 2 Under AM1.5 simulated sunlight irradiation, the current-voltage curves of the PM6:BTC-3 device were tested, and the results are as follows: Figure 5 As shown in the figure. The results show that the open-circuit voltage of the PM6:BTC-3 device is 0.773V, and the short-circuit current density is 27.76mA / cmm. 2 The fill factor is 77.37%, and the power conversion efficiency (PCE) is 16.60%.

[0137] Example 3

[0138] The assembly of semi-transparent organic solar cells based on the synthesized electron acceptor BTC-2 includes the following steps:

[0139] (1) Anode: The transparent conductive glass with strip-shaped ITO (anode) etched on the surface is cleaned by ultrasonic vibration with cleaning agent, deionized water, acetone and isopropanol in sequence, dried, and then treated with ultraviolet ozone for 10 minutes.

[0140] (2) Anode modification layer: A 2PACz transport layer was spin-coated onto the surface of the conductive glass with a 0.22 mg / mL 2PACz methanol solution, and then annealed at 100°C for 10 minutes.

[0141] (3) Active layer: Before spin-coating the active layer, a PM6:BTC-2 chloroform solution with an electron donor-to-acceptor mass ratio of 1:1.2 and a total concentration of 13 mg / mL was prepared, and 0.25% of 1,8-diiodooctane (DIO) was added as an additive. After stirring and dissolving at 60°C for 1 hour, the solution was spin-coated at 2500 rpm to obtain an active layer of approximately 60 nm. Then, the solution was annealed at 90°C for 5 minutes.

[0142] (4) Cathode modification layer: On the active layer prepared in step (3), a PDINN transport layer is spin-coated with a 1.5 mg / mL PDINN methanol solution.

[0143] (5) Cathode: Based on step (4), a 12nm Ag electrode is deposited using a vapor deposition apparatus to obtain an effective area of ​​6mm². 2 A semi-transparent organic solar cell, designated 12nm, with a tested area of ​​4.76mm². 2 .

[0144] At a light intensity of 100mW / cm 2 The current-voltage curves of the test device under AM1.5 simulated sunlight irradiation are shown in the following figures. Figure 6 As shown in the figure. The results show that the open-circuit voltage of the device numbered 12nm is 0.72V, and the short-circuit current density is 22.28mA / cm². 2 The fill factor is 75.09%, the power conversion efficiency (PCE) is 11.96%, the average light transmittance (APT) is 24.86%, and the light utilization efficiency (LUE) is 2.97% (LUE = PCE × APT).

[0145] Comparative Example 4

[0146] The semi-transparent organic solar cell was assembled based on the synthesized electron acceptor BTC-2, with the specific steps being the same as in Example 3, except that the thickness of the cathode Ag electrode was 14 nm, and it was assembled into a device numbered 14 nm.

[0147] At a light intensity of 100mW / cm 2 The current-voltage curves of the test device under AM1.5 simulated sunlight irradiation are shown in the following figures. Figure 6 As shown in the figure. The results show that the open-circuit voltage of the device numbered 14nm is 0.71V, and the short-circuit current density is 23.54mA / cm². 2 The fill factor is 74.56%, the power conversion efficiency (PCE) is 12.43%, the average light transmittance (APT) is 22.76%, and the light utilization efficiency (LUE) is 2.83%.

[0148] Comparative Example 5

[0149] The semi-transparent organic solar cell was assembled based on the synthesized electron acceptor BTC-2, with the specific steps being the same as in Example 3, except that the thickness of the cathode Ag electrode was 16 nm, and it was assembled into a device numbered 16 nm.

[0150] At a light intensity of 100mW / cm 2 The current-voltage curves of the test device under AM1.5 simulated sunlight irradiation are shown in the following figures. Figure 6 As shown in the figure. The results show that the open-circuit voltage of the device numbered 16nm is 0.71V, and the short-circuit current density is 23.73mA / cm². 2 The fill factor is 75.33%, the power conversion efficiency (PCE) is 12.67%, the average light transmittance (APT) is 21.41%, and the light utilization efficiency (LUE) is 2.71%.

[0151] Comparative Example 6

[0152] The semi-transparent organic solar cell was assembled based on the synthesized electron acceptor BTC-2. The specific steps were the same as in Example 3, except that the thickness of the cathode Ag electrode was 12nm, and a 45nm TeO2 optical layer was deposited on the Ag electrode to assemble the device numbered 12nm+TeO2.

[0153] At a light intensity of 100mW / cm 2 The current-voltage curves of the test device under AM1.5 simulated sunlight irradiation are shown in the following figures. Figure 6 As shown in the figure. The results show that the open-circuit voltage of the 12nm+TeO2 device is 0.70V, and the short-circuit current density is 20.39mA / cm². 2 The fill factor is 72.11%, the power conversion efficiency (PCE) is 10.31%, the average light transmittance (APT) is 35.19%, and the light utilization efficiency (LUE) is 3.63%.

[0154] Comparative Example 7

[0155] The semi-transparent organic solar cell was assembled based on the synthesized electron acceptor BTC-2. The specific steps were the same as in Example 3, except that the thickness of the cathode Ag electrode was 14 nm, and a 45 nm TeO2 optical layer was deposited on the Ag electrode to assemble the device numbered 14 nm+TeO2.

[0156] At a light intensity of 100mW / cm 2 The current-voltage curves of the test device under AM1.5 simulated sunlight irradiation are shown in the following figures. Figure 6 As shown in the figure. The results show that the open-circuit voltage of the 14nm+TeO2 device is 0.70V, and the short-circuit current density is 21.07mA / cm². 2 The fill factor is 74.65%, the power conversion efficiency (PCE) is 11.06%, the average light transmittance (APT) is 32.03%, and the light utilization efficiency (LUE) is 3.54%.

[0157] Comparative Example 8

[0158] The semi-transparent organic solar cell was assembled based on the synthesized electron acceptor BTC-2. The specific steps were the same as in Example 3, except that the thickness of the cathode Ag electrode was 16 nm, and a 45 nm TeO2 optical layer was deposited on the Ag electrode to assemble the device numbered 16 nm+TeO2.

[0159] At a light intensity of 100mW / cm 2 The current-voltage curves of the test device under AM1.5 simulated sunlight irradiation are shown in the following figures. Figure 6As shown in the figure. The results show that the open-circuit voltage of the 16nm+TeO2 device is 0.70V, and the short-circuit current density is 21.45mA / cm². 2 The fill factor is 75.41%, the power conversion efficiency (PCE) is 11.34%, the average light transmittance (APT) is 30.15%, and the light utilization efficiency (LUE) is 3.42%.

[0160] Example 4

[0161] The assembly of semi-transparent organic solar cells based on the synthesized electron acceptor BTC-2 includes the following steps:

[0162] (1) Anode: The transparent conductive glass with strip-shaped ITO (anode) etched on the surface is cleaned by ultrasonic vibration with cleaning agent, deionized water, acetone and isopropanol in sequence, dried, and then treated with ultraviolet ozone for 10 minutes.

[0163] (2) Anode modification layer: A 2PACz transport layer was spin-coated onto the surface of the conductive glass with a 0.22 mg / mL 2PACz methanol solution, and then annealed at 100°C for 10 minutes.

[0164] (3) Active layer: Before spin-coating the active layer, a PM6:BTC-2 chloroform solution with an electron donor-to-acceptor mass ratio of 1:1.2 and a total concentration of 13 mg / mL was prepared, and 0.25% of 1,8-diiodooctane (DIO) was added as an additive. After stirring and dissolving at 60°C for 1 hour, the solution was spin-coated at 3500 rpm to obtain an active layer of approximately 50 nm. Then, the solution was annealed at 90°C for 5 minutes.

[0165] (4) Cathode modification layer: On the active layer prepared in step (3), a PDINN transport layer is spin-coated with a 1.5 mg / mL PDINN methanol solution.

[0166] (5) Cathode: Based on step (4), a 12nm Ag electrode is deposited using a vapor deposition apparatus, followed by a 45nm thick TeO2 optical layer. This results in an effective area of ​​6mm². 2 The semi-transparent organic solar cell, numbered 1:1.2, has a test area of ​​4.76 mm². 2 .

[0167] At a light intensity of 100mW / cm 2 Under AM1.5 simulated sunlight irradiation, the current-voltage curves of device number 1:1.2 were tested, and the results are as follows: Figure 7 As shown in the figure. The results show that the open-circuit voltage of device number 1:1.2 is 0.71V, and the short-circuit current density is 18.52mA / cm². 2The fill factor is 74.37%, the power conversion efficiency (PCE) is 9.78%, the average light transmittance (APT) is 34.86%, and the light utilization efficiency (LUE) is 3.41%.

[0168] Comparative Example 9

[0169] Semi-transparent organic solar cells were assembled based on the synthesized electron acceptor BTC-2. The specific steps were the same as in Example 4, except that before spin-coating the active layer, a PM6:BTC-2 chloroform solution with an electron donor-to-acceptor mass ratio of 1:1.6 and a total concentration of 13 mg / mL was prepared.

[0170] At a light intensity of 100mW / cm 2 Under AM1.5 simulated sunlight irradiation, the current-voltage curves of device number 1:1.2 were tested, and the results are as follows: Figure 7 As shown in the figure. The results show that the open-circuit voltage of device number 1:1.6 is 0.72V, and the short-circuit current density is 19.58mA / cm². 2 The fill factor is 74.17%, the power conversion efficiency (PCE) is 10.39%, the average light transmittance (APT) is 43.51%, and the light utilization efficiency (LUE) is 4.52%.

[0171] Comparative Example 10

[0172] Semi-transparent organic solar cells were assembled based on the synthesized electron acceptor BTC-2. The specific steps were the same as in Example 4, except that before spin-coating the active layer, a PM6:BTC-2 chloroform solution with an electron donor-to-acceptor mass ratio of 1:2.0 and a total concentration of 13 mg / mL was prepared.

[0173] At a light intensity of 100mW / cm 2 Under AM1.5 simulated sunlight irradiation, the current-voltage curves of device number 1:2.0 were tested, and the results are as follows: Figure 7 As shown in the figure. The results show that the open-circuit voltage of device numbered 1:2.0 is 0.71V, and the short-circuit current density is 19.80mA / cm². 2 The fill factor is 75.18%, the power conversion efficiency (PCE) is 10.56%, the average light transmittance (APT) is 46.20%, and the light utilization efficiency (LUE) is 4.88%.

Claims

1. An ultra-narrow bandgap electron acceptor, characterized in that, BTC-1, BTC-2, or BTC-3 is used as the electron acceptor. The specific chemical structural formulas of the electron acceptors are as follows: 。 2. An active layer comprising an electron acceptor and an electron donor, said electron donor being a wide band gap polymeric donor material, characterized in that, The electron acceptor is the ultranarrow bandgap electron acceptor as described in claim 1.

3. The active layer according to claim 2, characterized in that, The weight ratio of the electron donor to the electron acceptor is 1:2 to 2:1, and the thickness of the active layer is 50 to 300 nm.

4. A method for preparing an active layer according to claim 2 or 3, characterized in that, The active layer is prepared by forming a film from a mixed solution of electron acceptor, electron donor and additive, and then annealing the film.

5. The method for preparing the active layer according to claim 4, characterized in that, The additive is 1,8-diiodooctane or chloronaphthalene, and the volume of the additive is 0.1-5% of the volume of the mixed solution of electron acceptor and electron donor.

6. The method for preparing the active layer according to claim 4, characterized in that, The annealing temperature for the annealing process is 80~200℃, and the annealing time is 5~30 min.

7. An organic solar cell comprising the active layer as described in claim 2 or 3.

8. The organic solar cell according to claim 7, comprising a substrate, an anode, an anode modification layer, an active layer, a cathode modification layer, and a cathode, characterized in that, The substrate is glass; the anode is ITO or FTO; the anode modification layer is 2PACz, PEDOT:PSS or MoO3; the electron donor in the active layer is PM6 or D18, and the electron acceptor is BTC-1, BTC-2 or BTC-3; the cathode modification layer is PDINN, PFN-Br or ZnO; the cathode is Ag.

9. The organic solar cell according to claim 8, characterized in that, The cathode Ag has a thickness of 10 nm to 100 nm, and an optical layer is modified on the cathode Ag.

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