An organic electron acceptor containing a carbazole side chain and its application

Abstract

The present invention discloses an organic electron acceptor containing a carbazole side chain and its application in solar cells. The organic electron acceptor containing a carbazole side chain has a structure shown in the following formula: #imgabs0# wherein R1 and R2 are independently a linear or branched alkyl group containing 1-18 carbon atoms, and A is an electron-withdrawing functional group. The present invention uses a non-fully fused ring structure based on trithiophene as the central conjugated skeleton of the organic electron acceptor, introduces a carbazole group as a side chain, prevents excessive elevation of the molecular HOMO energy level, and inhibits the internal rotation between the trithiophene rings connected by single bonds through its rigid large steric effect, thereby ensuring the planarity of the acceptor molecule, regulating the stacking between molecules, and simultaneously inhibiting the aromatic amine group from inducing the molecular skeleton to form a quinone structure, thereby improving the molecule's resistance to photooxidation.

Description

Technical Field

[0001] The present invention relates to the field of organic electron acceptors, and in particular to an organic electron acceptor containing a carbazole side chain and applications thereof. Background Art

[0002] Organic solar cells (OSCs) have broad application prospects in building-integrated photovoltaics, wearable devices, and indoor photovoltaics due to their lightweight, flexible, translucent, and large-area solution-processable properties. In recent years, with the successful development of organic fused-ring electron acceptors, particularly the Y-series electron acceptors, the power conversion efficiency (PCE) of OSCs has been significantly improved. The highest PCE for single-junction devices has reached over 19% (Joule 2019, 3, 1140; Adv. Mater. 2021, 33, 210-2420), meeting the efficiency requirements for practical applications. However, the Y-series electron acceptors, due to their complex structure, result in expensive material costs, making them unsuitable for large-scale applications. Therefore, the development of high-performance, low-cost organic electron acceptors is crucial to promoting the industrialization of OSCs.

[0003] Compared to fused-ring electron acceptors, non-fused-ring electron acceptors utilize intramolecular non-covalent interactions or steric hindrance to impart molecular planarity and even optoelectronic properties to the single-bonded conjugated backbone, similar to fused-ring structures. This greatly simplifies the synthesis process, thereby achieving low-cost organic electron acceptors (Adv. Mater. 2018, 30, 1705208). Fortunately, the recent development of non-fused-ring electron acceptors with large steric side chains has not only reduced synthesis costs but also achieved significant breakthroughs in corresponding battery efficiency. For example, the team of Hou Jianhui, a researcher at the Institute of Chemistry, Chinese Academy of Sciences, introduced triisopropylphenyl as a large steric side chain into a non-condensed ring acceptor of a tetrathiophene skeleton. The synthesized A4T-16 can enable the battery to achieve a PCE of up to 15.2% (Nat. Commun. 2021, 12, 5093); for another example, the team of Professor Bo Zhishan of Beijing Normal University introduced a diphenylamine side chain into a non-condensed ring acceptor of a trithiophene skeleton. The synthesized 2BTh-2F can increase the PCE of the battery to a record 15.44% (Adv. Energy Mater. 2021, 11, 2102591). However, the diphenylamine structure is extremely susceptible to photooxidation, which leads to poor stability and short life of organic electron acceptors based on such side chains and the solar cells constructed therefrom. In summary, there is currently a lack of high-efficiency, low-cost and long-life organic electron acceptors that meet practical requirements and need to be explored. Summary of the Invention

[0004] To address the above-mentioned technical problems and shortcomings in the art, the present invention provides an organic electron acceptor containing a carbazole side chain. By introducing a sterically hindered carbazole group as a side chain into the organic electron acceptor's terthiophene conjugated backbone, the acceptor achieves excellent photooxidation resistance while maintaining backbone planarity. Furthermore, organic solar cells constructed with this acceptor can simultaneously achieve high energy conversion efficiency and excellent photostability, facilitating future practical applications. Furthermore, the solar cell's absorption range primarily lies in the visible light region, making it suitable for indoor photovoltaic applications.

[0005] The specific technical solutions are as follows:

[0006] An organic electron acceptor containing a carbazole side chain has a structure shown in the following formula:

[0007]

[0008] Wherein, R1 and R2 are independently straight-chain or branched alkyl groups containing 1 to 18 carbon atoms, and A is an electron-withdrawing functional group.

[0009] In one embodiment, in the organic electron acceptor containing a carbazole side chain, R1 is a tert-butyl group.

[0010] In one embodiment, in the organic electron acceptor containing a carbazole side chain, R2 is an n-undecyl group.

[0011] The organic electron acceptor containing a carbazole side chain, A, can be any one of the following chemical structures:

[0012]

[0013] wherein X and Y are each independently a hydrogen atom, a halogen atom, a methyl group, a trifluoromethyl group or a methoxy group.

[0014] In one embodiment, the organic electron acceptor containing a carbazole side chain, A is

[0015] The present invention also provides application of the organic electron acceptor containing carbazole side chains in solar cells.

[0016] As a general inventive concept, the present invention also provides a solar cell comprising a substrate, an anode, a hole transport layer, an active layer, an electron transport layer and a cathode arranged in sequence from bottom to top, wherein the active layer is a blended film containing a polymer donor and the organic electron acceptor containing a carbazole side chain.

[0017] In the solar cell, the mass ratio of the polymer donor to the organic electron acceptor containing a carbazole side chain in the active layer can be 3:1-9.

[0018] In the solar cell, the polymer donor may be PM6.

[0019] In the solar cell, the thickness of the active layer may be 40 to 300 nm.

[0020] In one embodiment, in the solar cell, the substrate is glass; the anode is ITO; the hole transport layer is PEDOT:PSS; the electron transport layer is PDINN; and the cathode is Ag.

[0021] The present invention provides an organic electron acceptor with simple synthesis, which uses terthiophene as a conjugated skeleton and introduces a carbazole side chain as a large steric hindrance group. While ensuring the planarity of the molecule, the photooxidation resistance of the acceptor molecule is enhanced, thereby improving the PCE and light stability of the organic solar cell.

[0022] The present invention uses a non-fully fused ring structure based on trithiophene as the central conjugated skeleton of the organic electron acceptor, introduces a carbazole group as a side chain to prevent excessive elevation of the HOMO energy level of the molecule, and through its rigid large steric effect, inhibits the internal rotation between the trithiophene rings connected by single bonds, ensures the planarity of the acceptor molecule, regulates the stacking between molecules, and simultaneously inhibits the aromatic amine group from inducing the molecular skeleton to form a quinone structure, thereby improving the molecule's resistance to photooxidation.

[0023] The beneficial effects of the present invention are:

[0024] 1. The designed receptor molecule has a simple structure, is easy to synthesize, and the raw materials are readily available and low in cost, which is conducive to practical application.

[0025] 2. The carbazole side chain non-condensed ring organic electron acceptor obtained by the present invention and the organic solar cell constructed therefrom have better photostability and lifespan while maintaining a high PCE, and have high practical value.

[0026] 3. Due to the lower HOMO energy level and wider band gap, the absorption spectrum of this type of electron acceptor is mainly in the visible light region. Therefore, the solar cells constructed based on this type of electron acceptor are very suitable for indoor photovoltaic use. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the molecular structure of the organic electron acceptor 3TTCz containing a carbazole side chain and the organic electron acceptor 3TTDPA containing a diphenylamine side chain.

[0028] Figure 2 The UV-visible absorption spectra of thin films of organic electron acceptor 3TTCz containing carbazole side chains and organic electron acceptor 3TTDPA containing diphenylamine side chains.

[0029] Figure 3This is the energy level test results of the organic electron acceptor 3TTCz containing a carbazole side chain and the organic electron acceptor 3TTDPA containing a diphenylamine side chain.

[0030] Figure 4 1 is a voltage-current curve diagram of the organic solar cell 1 of the embodiment and the organic solar cell of the comparative example under simulated sunlight.

[0031] Figure 5 1 is a comparison chart of the stability results of the organic solar cell 1 of the embodiment and the organic solar cell of the comparative example under continuous irradiation of simulated sunlight. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the accompanying drawings and specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0033] In the following examples, the operating methods without specifying specific conditions are generally carried out under conventional conditions or conditions recommended by the manufacturer.

[0034] Example

[0035] Organic electron acceptor 3TTCz with carbazole side chain (molecular structure see Figure 1 ) synthesis:

[0036]

[0037] Step 1: Synthesis of compound 2

[0038] Compound 1 (1 g, 3.35 mmol), (3,6-di-tert-butyl)carbazole (3.74 g, 13.4 mmol), NaOtBu (1.93 g, 20.1 mmol) and o-xylene (50 mL) were added to a 100 mL reaction flask. The resulting mixture was frozen with liquid nitrogen and evacuated with Ar gas three times to maintain an Ar atmosphere in the reaction flask. After thawing, Pd(OAc)2 (37.7 mg, 0.17 mmol) and P(t-Bu)3 (1.01 mL, 1.01 mmol) were added under Ar gas flow, and the mixture was heated to 145°C and refluxed for 96 h. After the reaction was completed, the mixture was extracted with water and dichloromethane, and the organic phase was distilled under reduced pressure to remove the solvent, washed with petroleum ether, and filtered to obtain a white solid product 2 (680.2 mg, 37%). H (500MHz, CDCl3): 8.19(s,4H), 7.55(s,2H), 7.52(d,4H), 7.44(d,4H), 1.46-1.53(m,36H).

[0039] Step 2: Synthesis of compound 3

[0040] Compound 2 (200 mg, 0.288 mmol), N-bromosuccinimide (NBS, 112.84 mg, 0.634 mmol), chloroform (20 mL), and N,N-dimethylformamide (DMF, 5 mL) were added to a 100 mL reaction flask and stirred to dissolve thoroughly. The mixture was reacted at room temperature for 12 h. After the reaction was completed, the mixture was quenched with saturated NaHCO3, separated by extraction, and the organic phase was separated. The solvent was removed by vacuum distillation and then purified by silica gel column chromatography (eluent: DCM (dichloromethane): PE (petroleum ether) = 1:1, v / v) to obtain a white solid product 3 (218.14 mg, 89.1%). H (500MHz, CDCl3): 8.17(s,4H), 7.53(d,4H), 7.22(d,4H), 1.44-1.52(m,36H).

[0041] Step 3: Synthesis of compound 5

[0042] Compound 3 (200 mg, 0.235 mmol), compound 4 (468.11 mg, 0.965 mmol), toluene (20 mL), and DMF (2 mL) were added to a reaction flask. The resulting mixture was frozen with liquid nitrogen and evacuated three times with Ar gas to maintain an Ar atmosphere in the reaction flask. Pd(PPh3)4 (16.3 mg, 0.014 mmol) was added under Ar gas flow, and then evacuated three times. After thawing, the mixture was heated to 110°C and refluxed for 24 hours. After the reaction was completed, the mixture was washed with water, extracted, and the organic phase was taken. After removing the solvent by vacuum distillation, it was purified by silica gel column (eluent: DCM:PE=2:1, v / v) to obtain an orange solid product 5 (261.3 mg, 84.2%). H (500MHz, CDCl3): 9.94(s,2H), 8.23(s,4H), 7.47(d,4H), 7.18(d,4H), 6.99(s,2H), 1.42-1.50(m,36H), 1.11-1.32(m,46H).

[0043] Step 4: Synthesis of compound 6 (3TTCz)

[0044] Compound 5 (200 mg, 0.151 mmol), bis(fluoro-IC)-terminated (DFIC, 139.38 mg, 0.604 mmol), and chloroform (30 mL) were added to a 100 mL reaction flask, stirred, and heated to 83°C. 0.2 mL of pyridine was added dropwise, and the mixture was heated under reflux for 12 h. After completion of the reaction, the solvent was removed by distillation under reduced pressure, and the product was purified by silica gel column chromatography (eluent: DCM:PE = 1:2, v / v). Finally, precipitation with methanol afforded the product 6 (162.89 mg, 61.2%) as a dark blue solid. 1H NMR (500MHz, CDCl3): 8.94(s,2H), 8.48-8.54(m,2H), 8.26(s,4H), 7.60-7.65(m,2 H), 7.48(d,4H), 7.18(d,4H), 6.99(s,2H), 1.42-1.54(m,36H), 1.09-1.32(m,46H). MS(MALDI-TOF):Calcd for C 106 H 102 F4N6O2S6(M+):1760.38,Found:1759.56.

[0045] Absorption spectrum characterization of organic electron acceptor 3TTCz containing carbazole side chain: 3TTCz was dissolved in chloroform to prepare a solution, which was spin-coated on a quartz plate to prepare a thin film sample. The UV-visible absorption spectrum of the acceptor in the thin film state was measured. The measured spectrum is listed in Figure 2 .

[0046] Energy level characterization of the organic electron acceptor 3TTCz containing a carbazole side chain: A chloroform solution of 8 mg / mL 3TTCz was prepared, and a 0.1 mol / L acetonitrile solution of tetrabutylammonium hexafluorophosphate was used as the electrolyte. A platinum disk, a platinum wire, and a standard calomel electrode (SCE) were used as the working electrode, counter electrode, and reference electrode, respectively. The scan range was set to -1.0 to 1.5 V, the scan rate was 0.05 V / s, and the sampling interval was 0.001 V. The CV curves of the samples were measured. The obtained curves are listed in Figure 3 After obtaining the curve, the LUMO and HOMO energy levels of the molecule were calculated using the potential of a standard calomel electrode as a reference, which was calibrated using the redox pair of ferrocene (Fc / Fc+) at -4.8 eV.

[0047] Solar cell I using the organic electron acceptor 3TTCz with carbazole side chains: A transparent conductive glass substrate coated with ITO strips (anode) was cleaned sequentially with alkaline solution, deionized water, acetone, isopropyl alcohol, and ethanol, followed by ultrasonic cleaning with alkali, deionized water, acetone, isopropyl alcohol, and ethanol, followed by drying and ozone treatment for 20 minutes. A hole-transport layer, PEDOT:PSS, was then spin-coated at 4500 rpm for 20 seconds and annealed at 150°C for 20 minutes. The annealed substrate was transferred to a nitrogen-filled glove box. A chloroform mixture of PM6:3TTCz (17 mg / mL in a mass ratio) was then spin-coated at 3500 rpm to form a film. The film was then annealed on a 100°C hotplate for 10 minutes. Then, the electron transport layer PDINN was spin-coated, and finally a 110 nm thick silver electrode was deposited by vacuum evaporation to obtain an organic cell I with the structure of ITO / PEDOT:PSS / PM6:3TTCz / PDINN / Ag. 2 The current-voltage curve of the battery was tested under AM1.5 simulated sunlight, and the obtained curve is listed in Figure 4 The final open circuit voltage was 0.941V and the short circuit current density was 18.90mA / cm 2 , the fill factor is 78.78% and the power conversion efficiency (PCE) is 14.00%.

[0048] Solar Cell II using the organic electron acceptor 3TTCz with carbazole side chains: A transparent conductive glass substrate coated with ITO strips (anode) was cleaned with alkali, deionized water, acetone, isopropyl alcohol, and ethanol, followed by ultrasonic cleaning with alkali, deionized water, acetone, isopropyl alcohol, and ethanol. The substrate was then dried and treated with ozone for 20 minutes. A hole-transport layer, PEDOT:PSS, was then spin-coated at 4500 rpm for 20 seconds and annealed at 150°C for 20 minutes. The annealed substrate was then transferred to a nitrogen-filled glove box. A chloroform mixture of PM6:3TTCz (17 mg / mL, mass ratio, total concentration) was then spin-coated at 3500 rpm to form a film. The film was then annealed on a 100°C hotplate for 10 minutes. Then, the electron transport layer PDINN was spin-coated, and finally a 110nm thick silver electrode was deposited by vacuum evaporation to obtain an organic cell II with the structure of ITO / PEDOT:PSS / PM6:3TTCz / PDINN / Ag. 2 The current-voltage curve of the battery was tested under AM1.5 simulated sunlight, and the final open circuit voltage was 0.946V and the short circuit current density was 18.06mA / cm 2 , the filling factor is 75.02% and the power conversion efficiency (PCE) is 12.82%.

[0049] Stability of organic solar cells I constructed with organic electron acceptors containing carbazole side chains: The light stability of the cells was tested under continuous irradiation with simulated sunlight, provided by a metal halide lamp (Philips MSR 1200HR) without UV filtering. The test results are listed in Figure 5 The organic solar cell showed nonlinear performance degradation within 250 hours, but at 250 hours, the organic solar cell still retained 60% of its energy conversion efficiency.

[0050] Comparative Example

[0051] The organic electron acceptor 3TTCz containing a carbazole side chain was prepared by a similar procedure as in Example 1, except that (3,6-di-tert-butyl)carbazole was replaced by an equimolar amount of 4,4'-di-tert-butyldiphenylamine, and the rest of the steps were the same to obtain a dark blue solid 3TTDPA (molecular structure see Figure 1 ). 1 H NMR (500MHz, CDCl3): δ = 8.99 (s, 2H), 8.52 (dd, J = 10.0, 6.4Hz, 2H), 7.65 (t, J = 7.5Hz, 2H), 7.31 (d, J = 8. 7Hz,8H),7.19(s,2H),7.08(d,J=8.7Hz,8H),1.60(s,36H),1.32-1.21(m,46H).MS(MALDI-TOF):Calcd for C 106 H 106 F4N6O2S6(M+):1764.41,Found:1763.93.

[0052] Absorption spectrum characterization of the organic electron acceptor 3TTDPA containing diphenylamine side chains: 3TTDPA was dissolved in chloroform to prepare a solution, which was spin-coated on a quartz plate to prepare a thin film sample. The UV-visible absorption spectrum of the acceptor in the thin film state was measured. The measured spectrum is listed in Figure 2 .

[0053] Characterization of the energy level of the organic electron acceptor 3TTDPA containing a diphenylamine side chain: 8 mg / mL 3TTCz chloroform solution was prepared, 0.1 mol / L tetrabutylammonium hexafluorophosphate in acetonitrile solution was used as the electrolyte, a platinum disk, a platinum wire, and a standard calomel electrode (SCE) were used as the working electrode, counter electrode, and reference electrode, respectively. The scanning range was set to -1.0 to 1.5 V, the scanning speed was 0.05 V / s, and the sampling interval was 0.001 V. The CV curve of the sample was measured. The obtained curve is listed in Figure 3After obtaining the curve, the LUMO and HOMO energy levels of the molecule were calculated using the potential of a standard calomel electrode as a reference, which was calibrated using the redox pair of ferrocene (Fc / Fc+) at -4.8 eV.

[0054] Solar cells were constructed using 3TTDPA, an organic electron acceptor with diphenylamine side chains (the parameters and conditions below represent the optimized conditions for 3TTDPA solar cells): A transparent conductive glass substrate coated with ITO strips (anode) was cleaned with alkali, deionized water, acetone, isopropyl alcohol, and ethanol, followed by ultrasonic cleaning, drying, and ozone treatment for 20 minutes. A hole-transport layer, PEDOT:PSS, was then spin-coated at 4500 rpm for 20 seconds and annealed at 150°C for 15 minutes. The annealed substrate was transferred to a nitrogen glove box. A chloroform mixture of PM6:3TTDPA (17 mg / mL in a mass ratio) with 1 wt% DIO (1,8-diiodooctane) was then spin-coated at 3500 rpm and annealed on a 100°C hotplate for 10 minutes. Then, the electron transport layer PDINN was spin-coated, and finally a 110nm thick silver electrode was deposited by vacuum evaporation to obtain an organic solar cell with the structure of ITO / PEDOT:PSS / PM6:3TTDPA / PDINN / Ag. 2 The current-voltage curve of the battery was tested under AM1.5 simulated sunlight, and the obtained curve is listed in Figure 4 The final open circuit voltage was 0.940V and the short circuit current density was 21.97mA / cm 2 , the fill factor is 66.93% and the power conversion efficiency (PCE) is 13.85%.

[0055] Stability of organic solar cells constructed with 3TTDPA, an organic electron acceptor containing diphenylamine side chains: The light stability of the cells was tested under continuous irradiation with simulated sunlight, provided by a metal halide lamp (Philips MSR 1200HR) without UV filtering. The test results are listed in Figure 5 In the experiment, the organic solar cell showed nonlinear performance degradation within 250 hours. At 250 hours, the organic solar cell only retained 11% of the energy conversion efficiency.

[0056] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. An organic electron acceptor containing a carbazole side chain, characterized in that: It has the following structure: Wherein, R1 and R2 are each independently a linear or branched alkyl group containing 1 to 18 carbon atoms, and A is any one of the following chemical structures: wherein X and Y are each independently a hydrogen atom, a halogen atom, a methyl group, a trifluoromethyl group or a methoxy group.

2. The organic electron acceptor containing a carbazole side chain according to claim 1, characterized in that R1 is tert-butyl.

3. The organic electron acceptor containing a carbazole side chain according to claim 1, characterized in that: R2 is n-undecyl.

4. The organic electron acceptor containing a carbazole side chain according to claim 1, characterized in that A is 5. Use of the organic electron acceptor containing a carbazole side chain according to any one of claims 1 to 4 in solar cells.

6. A solar cell comprising a substrate, an anode, a hole transport layer, an active layer, an electron transport layer and a cathode arranged in order from bottom to top, characterized in that: The active layer is a blended film containing a polymer donor and the organic electron acceptor containing a carbazole side chain according to any one of claims 1 to 4.

7. The solar cell according to claim 6, characterized in that The mass ratio of the polymer donor to the organic electron acceptor containing a carbazole side chain in the active layer is 3:1 to 9; The polymer donor is PM6; The thickness of the active layer is 40 to 300 nm.

8. The solar cell according to claim 6 or 7, characterized in that: The substrate is glass; the anode is ITO; the hole transport layer is PEDOT:PSS; the electron transport layer is PDINN; and the cathode is Ag.

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