Benzodithiophene-fused benzothiadiazole conjugated polymer as well as preparation method and application thereof

Abstract

The invention discloses a benzodithiophene-fused benzothiadiazole conjugated polymer as well as a preparation method and application thereof, and belongs to the technical field of organic photoelectric materials. The benzodithiophene-fused benzothiadiazole conjugated polymer provided by the invention has a chemical structural formula as shown in a formula I or a formula II, a benzothiadiazole unit and a pi-bridge structure are introduced into a conjugated skeleton, and alkyl chain modification is combined, so that the matching degree with a solar spectrum, the carrier migration rate and the material solubility are remarkably improved. The number-average molecular weight of the polymer is 11-45 kDa, the dispersion coefficient is 1.75-3.06, an efficient electron transmission channel can be constructed in an organic photovoltaic cell device, excellent photoelectric conversion efficiency is finally achieved, the preparation method is simple, the polymer has practical application value, and the polymer has wide application prospects in preparation of the organic photovoltaic cell device.

Description

Technical Field

[0001] This application belongs to the technical field of organic optoelectronic materials, and particularly relates to a benzodithiophene-fused benzothiadiazole-based conjugated polymer, a preparation method thereof, and an application thereof. Background Art

[0002] Organic solar cells have become a research hotspot in recent years due to their relatively simple preparation process, relatively low raw material prices, variability in material design, and the possibility of large-area preparation. Among them, the research on two-component or multi-component bulk heterojunction solar cells is the most in-depth, and they have excellent energy conversion efficiency; however, such devices have disadvantages such as many optimization steps and poor stability, which are not conducive to the long-term development of organic solar cells. Therefore, it is necessary to develop polymers with excellent comprehensive properties to expand the application scenarios.

[0003] The prior art with the application publication number CN 103833977A discloses a copolymer containing benzodithiophene-thieno[3,2-b]thiophene[2,3-d]benzothiadiazole. This polymer has a high degree of matching with the solar spectrum, and at the same time has a planar conjugated structure and a high carrier migration rate, which can increase the proportion of carriers reaching the electrode and the charge collection efficiency, thereby improving the energy conversion efficiency. Moreover, by improving or modifying the device structure, a higher energy conversion efficiency can be obtained.

[0004] However, the above polymer has the following problems: First, the design of the conjugated unit results in a narrow spectral absorption range, making it difficult to fully utilize solar radiation energy; second, the lack of molecular structure regularity hinders the carrier migration path, and the optoelectronic conversion efficiency needs to be improved; at the same time, the means for regulating the solubility and molecular weight of the polymer are limited, restricting the film-forming quality and device stability. It is urgent to develop conjugated polymers with better comprehensive properties through structural optimization. Summary of the Invention

[0005] This application discloses a benzodithiophene-fused benzothiadiazole-based conjugated polymer, a preparation method thereof, and an application thereof, aiming to solve the technical problems of the deficiencies in spectral matching, processing performance, and optoelectronic conversion efficiency of existing conjugated polymers and the narrow range of options.

[0006] To achieve the above object, the technical solution of this application is:

[0007] The first aspect of this application provides a benzodithiophene-fused benzothiadiazole-based conjugated polymer, which has a chemical structural formula shown in Formula I or Formula II:

[0008]

[0009] In Formula I, R1 and R2 are independently selected from hydrogen, a linear or branched alkyl group with C1-C 20 and a linear or branched alkyl group with C6-C 20a cycloalkyl group, a C1-C 20 a straight-chain or branched alkoxy group, or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; n is a natural number from 10 to 1000;

[0010]

[0011] In Formula II, R1 and R2 are each independently selected from hydrogen, a C1-C 20 straight-chain or branched alkyl group, a C6-C 20 cycloalkyl group, a C1-C 20 straight-chain or branched alkoxy group, or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; the π-bridge is selected from one of thiophene, thiophene with an alkyl chain, thiophene with a halogen element, thiophene containing both an alkyl chain and a halogen, benzene, benzene with an alkyl chain, benzene with a halogen element, benzene containing both an alkyl chain and a halogen, and a biphenyl linking unit; n is a natural number from 10 to 1000.

[0012] Preferably, in combination with the first aspect, in Formula I, R1 and R2 are each independently selected from a C1-C 20 straight-chain or branched alkyl group;

[0013] In Formula II, R1 and R2 are each independently selected from a C1-C 20 straight-chain or branched alkyl group.

[0014] Preferably, in combination with the first aspect, the number-average molecular weight of the benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer is 11 - 45 kDa, and the dispersity is 1.75 - 3.06.

[0015] The second aspect of the present application provides a method for preparing the benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer described in the first aspect, and the preparation method includes:

[0016] providing Compound A and Compound B;

[0017] under an inert gas atmosphere and in the presence of a catalyst, carrying out a Stille coupling reaction on the Compound A and Compound B in an organic solvent, and separating and purifying to obtain the benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer;

[0018] Compound A has the chemical structural formula shown in Formula III:

[0019]

[0020] In Formula III, R1 is selected from hydrogen, a C1-C 20 straight-chain or branched alkyl group, a C6-C 20 cycloalkyl group, a C1-C 20one of a straight-chain or branched-chain alkoxy group or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine.

[0021] Compound B has a chemical structural formula shown in Formula IV or Formula V:

[0022]

[0023] In Formula IV or Formula V, R2 is selected from hydrogen, a C1-C 20 straight-chain or branched-chain alkyl group, a C6-C 20 cycloalkyl group, a C1-C 20 straight-chain or branched-chain alkoxy group, or an aryl group containing one or more aromatic rings; the π-bridge is selected from one of thiophene, thiophene with an alkyl chain, thiophene with a halogen element, thiophene containing both an alkyl chain and a halogen, benzene, benzene with an alkyl chain, benzene with a halogen element, benzene containing both an alkyl chain and a halogen, and a biphenyl linking unit.

[0024] Preferably in combination with the second aspect, the molar ratio of Compound A to Compound B is 1:1.

[0025] Preferably in combination with the second aspect, when performing the Stille coupling reaction, the reaction temperature is 100 - 120 °C and the reaction time is 6 hours.

[0026] Preferably in combination with the second aspect, the catalyst is one or several of tris(dibenzylideneacetone)dipalladium, bis(triphenylphosphine)palladium dichloride, or tetrakis(triphenylphosphine)palladium.

[0027] Preferably in combination with the second aspect, the organic solvent is one or several of tetrahydrofuran, ethylene glycol dimethyl ether, benzene, and toluene.

[0028] Preferably in combination with the second aspect, the operation of separation and purification is as follows: cooling the mixture to room temperature and precipitating with 100 ml of methanol, extracting successively with methanol, acetone, hexane, dichloromethane, and chloroform until the extract is colorless, then concentrating with methanol and performing vacuum filtration to obtain a benzodithiophene-fused benzothiadiazole-based conjugated polymer.

[0029] The third aspect of the present application provides the use of the benzodithiophene-fused benzothiadiazole-based conjugated polymer described in the first aspect or the benzodithiophene-fused benzothiadiazole-based conjugated polymer prepared by the preparation method described in the second aspect in the preparation of an organic photovoltaic cell device.

[0030] Compared with the prior art, the advantages or beneficial effects of the embodiments of the present application at least include: The benzodithiophene-fused benzothiadiazole-based conjugated polymer provided by the present application contains a novel benzothiadiazole conjugated unit. On the one hand, it has a high degree of matching with the solar spectrum and can absorb light energy more effectively. On the other hand, by introducing alkyl groups, the solubility and molecular weight of the copolymer are increased, which is beneficial to film-forming processing and provides convenience for practical applications. Thirdly, this conjugated polymer has a relatively high number-average molecular weight and a relatively narrow polydispersity index. When applied in a forward device, it is beneficial to construct a more effective electron transport channel in the active layer; the planar conjugated structure enables a high carrier migration rate, can increase the proportion of carriers reaching the electrodes and the charge collection efficiency, and ultimately improves the photoelectric conversion efficiency, showing broad application prospects in organic photovoltaic cell devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some of the embodiments recorded in the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is the ultraviolet-visible absorption spectrum diagram of the conjugated polymer prepared in the embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present application.

[0034] In the following description of this embodiment, the term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, B exists alone, and both A and B exist simultaneously. Wherein A and B may be singular or plural.

[0035] In the following description of this embodiment, the term "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or a similar expression refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0036] Those skilled in the art should understand that in the following description of the embodiments of this application, the sequence numbers do not imply the order of execution, and some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0037] The terms used in the embodiments of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The singular forms "a" and "the" used in the embodiments of this application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0038] It should be noted that all raw materials and reagents in the embodiments of this application are purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0039] In a first aspect, the embodiments of this application provide a benzodithiophene-fused benzothiadiazole-based conjugated polymer having a chemical structural formula shown in Formula I or Formula II:

[0040]

[0041] In Formula I, R1 and R2 are independently selected from one of hydrogen, a linear or branched alkyl group having 1 - C 20 a cycloalkyl group having 6 - C 20 a linear or branched alkoxy group having 1 - C 20 an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; n is a natural number from 10 to 1000.

[0042]

[0043] In Formula II, R1 and R2 are independently selected from one of hydrogen, a linear or branched alkyl group having 1 - C 20 a cycloalkyl group having 6 - C 20 a linear or branched alkoxy group having 1 - C 20One of an alkoxy group having a linear or branched chain, or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; the π-bridge is selected from one of thiophene, thiophene with an alkyl chain, thiophene with a halogen element, thiophene containing both an alkyl chain and a halogen, benzene, benzene with an alkyl chain, benzene with a halogen element, benzene containing both an alkyl chain and a halogen, and a biphenyl linking unit; n is a natural number from 10 to 1000.

[0044] Among them, the benzodithiophene-fused benzothiadiazole-based conjugated polymer provided by this application contains a novel benzothiadiazole conjugated unit. On the one hand, it has a high degree of matching with the solar spectrum and can absorb light energy more effectively; on the other hand, by introducing alkyl groups, the solubility and molecular weight of the copolymer are increased, which is beneficial to film-forming processing and provides convenience for practical applications; on the third hand, this conjugated polymer has a relatively high number-average molecular weight and a relatively narrow polydispersity index. When applied in a forward device, it is beneficial to construct a more effective electron transport channel in the active layer; the planar conjugated structure enables a high carrier migration rate, can increase the proportion of carriers reaching the electrode and the charge collection efficiency, and ultimately improves the photoelectric conversion efficiency, showing broad application prospects in organic photovoltaic cell devices.

[0045] It should be noted that through strategies such as non-halogenation, fluorination, chlorination, changing the alkyl chain length, changing the alkyl chain position, and introducing a π-bridge, this application has obtained a series of high-performance polymer donors with good performance.

[0046] In the examples of this application, in formula I, R1 and R2 are independently selected from straight-chain or branched-chain alkyl groups of C1-C 20 In formula II, R1 and R2 are independently selected from straight-chain or branched-chain alkyl groups of C1-C 20 straight-chain or branched-chain alkyl groups.

[0047] In the examples of this application, the number-average molecular weight of the benzodithiophene-fused benzothiadiazole-based conjugated polymer is preferably 11-45 kDa, and the dispersity coefficient is preferably 1.75-3.06. Among them, the prepared polymer has a relatively high number-average molecular weight and a relatively narrow polydispersity index. When applied in a forward device, it is beneficial to construct a more effective electron transport channel in the active layer.

[0048] Second, the examples of this application also provide a preparation method of the benzodithiophene-fused benzothiadiazole-based conjugated polymer described in the first aspect. The preparation method includes:

[0049] Providing compound A and compound B;

[0050] Under an inert gas atmosphere and catalyst conditions, carrying out a Stille coupling reaction on the compound A and compound B in an organic solvent, followed by separation and purification to obtain the benzodithiophene-fused benzothiadiazole-based conjugated polymer;

[0051] Compound A has the chemical structural formula shown in Formula III:

[0052]

[0053] In Formula III, R1 is selected from one of hydrogen, a linear or branched alkyl group having 1 to C 20 a linear or branched cycloalkyl group having 6 to C 20 a linear or branched alkoxy group having 1 to C 20 or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine.

[0054] Compound B has the chemical structural formula shown in Formula IV or Formula V:

[0055]

[0056] In Formula IV or Formula V, R2 is selected from one of hydrogen, a linear or branched alkyl group having 1 to C 20 a linear or branched cycloalkyl group having 6 to C 20 a linear or branched alkoxy group having 1 to C 20 or an aryl group containing one or more aromatic rings; the π-bridge is selected from one of thiophene, thiophene with an alkyl chain, thiophene with a halogen element, thiophene containing both an alkyl chain and a halogen, benzene, benzene with an alkyl chain, benzene with a halogen element, benzene containing both an alkyl chain and a halogen, and a biphenyl linking unit.

[0057] It should be noted that the reaction equation of the benzodithiophene-fused benzothiadiazole-based conjugated polymer prepared in this application is shown as follows 1 or 2:

[0058]

[0059] In the examples of this application, the molar ratio of Compound A and Compound B is 1:1. Among them, by controlling the molar ratio of Compound A (benzodithiophene tin salt) and Compound B (thiadiazole), a conjugated polymer with regular structure, excellent performance, and high purity can be obtained, meeting the requirements of organic photovoltaic cell devices for material performance.

[0060] In the examples of this application, when carrying out the Stille coupling reaction, the reaction temperature is 100 - 120 °C, and the reaction time is 6 hours. Among them, by controlling the reaction time and temperature, the occurrence of side reactions can be reduced, and the quality of the polymer can be guaranteed.

[0061] It should be noted that when this application is applied in a forward device, the preferred acceptor material is selected as Y6, and its molecular structural formula is shown in Formula VI:

[0062]

[0063] In a third aspect, the embodiments of the present application also provide an application of the benzodithiophene-fused benzothiadiazole-based conjugated polymer described in the first aspect or the benzodithiophene-fused benzothiadiazole-based conjugated polymer prepared by the preparation method described in the second aspect in the preparation of organic photovoltaic cell devices. Among them, based on the above-prepared polymer having a relatively high number-average molecular weight and a relatively narrow polydispersity index, when applied in a forward device, it is beneficial to construct a more effective electron transport channel in the active layer, improve the short-circuit current and fill factor of the battery, and ultimately improve the photoelectric conversion efficiency, having broad application prospects.

[0064] The technical solution of the present application will be further elaborated below in conjunction with specific embodiments.

[0065] Example 1

[0066] This example provides a preparation method for an A1-benzodithiophene-fused benzothiadiazole-based conjugated polymer (PBDT-CBT), which specifically includes:

[0067] BDT-2Sn (90.5 mg, 0.1 mmol) and CBT-2Br (55.3 mg, 0.1 mmol) were added to a reaction flask equipped with a magnetic stirrer. Then the vial was transferred to a glove box protected by N2, where Pd2(dba)3 (9.25 mg, 0.008 mmol) and anhydrous chlorobenzene (7 mL) were added to obtain a mixture. The reaction mixture was sealed and heated at 110 °C for 6 hours. The mixture was cooled to room temperature and precipitated with 100 mL of methanol. Then the crude polymer was successively extracted with methanol, acetone, hexane, dichloromethane and chloroform until the extract was colorless. The chloroform solution was concentrated and precipitated in methanol. The precipitate was filtered and dried under vacuum to obtain 0.092 g of a dark solid polymer, namely A1-benzodithiophene-fused benzothiadiazole-based conjugated polymer (denoted as PBDT-CBT).

[0068] The purified A1-benzodithiophene-fused benzothiadiazole-based conjugated polymer (PBDT-CBT) was subjected to GPC testing, and the number-average molecular weight M n = 14.64 kDa, and the polymer polydispersity (PDI) was 1.75.

[0069] Its synthetic route is as follows:

[0070]

[0071] Example 2

[0072] This example provides a preparation method for an A2-benzodithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF-CBT), which specifically includes:

[0073] BDTF-2Sn (94.1 mg, 0.1 mmol) and CBT-2Br (55.3 mg, 0.1 mmol) were added to a reaction flask equipped with a magnetic stirrer. Then the vial was transferred to a glove box protected by N2, where Pd2(dba)3 (9.25 mg, 0.008 mmol) and anhydrous chlorobenzene (7 mL) were added to obtain a mixture. The reaction mixture was sealed and heated at 110 °C for 6 h. The mixture was cooled to room temperature and precipitated with 100 mL of methanol. Then the crude polymer was successively extracted with methanol, acetone, hexane, dichloromethane and chloroform until the extract was colorless. The chloroform solution was concentrated and precipitated in methanol. The precipitate was filtered and dried under vacuum to obtain 0.094 g of a dark solid polymer, namely A2-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (denoted as PBDTF-CBT).

[0074] The purified A2-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF-CBT) was subjected to GPC testing, and the number-average molecular weight M n = 18.05 kDa, and the polydispersity index (PDI) of the polymer was 2.20.

[0075] The synthetic route is as follows:

[0076]

[0077] Example 3

[0078] This example provides a preparation method of A3-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTCl-CBT), which specifically includes:

[0079] BDTCl-2Sn (97.3 mg, 0.1 mmol) and CBT-2Br (55.3 mg, 0.1 mmol) were added to a reaction flask equipped with a magnetic stirrer. Then the vial was transferred to a glove box protected by N2, where Pd2(dba)3 (9.25 mg, 0.008 mmol) and anhydrous chlorobenzene (7 mL) were added to obtain a mixture. The reaction mixture was sealed and heated at 110 °C for 6 h. The mixture was cooled to room temperature and precipitated with 100 mL of methanol. Then the crude polymer was successively extracted with methanol, acetone, hexane, dichloromethane and chloroform until the extract was colorless. The chloroform solution was concentrated and precipitated in methanol. The precipitate was filtered and dried under vacuum to obtain 0.093 g of a dark solid polymer, namely A3-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (denoted as PBDTCl-CBT).

[0080] The purified A3-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTCl-CBT) was subjected to GPC testing, and the number-average molecular weight M n= 17.93 kDa, and the polydispersity index (PDI) of the polymer is 3.06.

[0081] The synthetic route is as follows:

[0082]

[0083] Example 4

[0084] This example provides a method for preparing an A4-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF-CBT(BO)), which specifically includes:

[0085] BDTF-2Sn (94.1 mg, 0.1 mmol) and CBT(BO)-2Br (60.9 mg, 0.1 mmol) were added to a reaction flask equipped with a magnetic stirrer. Then the vial was transferred to a glove box protected by N2, and Pd2(dba)3 (9.25 mg, 0.008 mmol) and anhydrous chlorobenzene (7 mL) were added to obtain a mixture. The reaction mixture was sealed and heated at 110 °C for 6 hours. The mixture was cooled to room temperature and precipitated with 100 mL of methanol. Then the crude polymer was successively extracted with methanol, acetone, hexane, dichloromethane, and chloroform until the extract was colorless. The chloroform solution was concentrated and precipitated in methanol. The precipitate was filtered and dried under vacuum to obtain 0.102 g of a dark solid polymer, namely A4-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (denoted as PBDTF-CBT(BO)).

[0086] The purified A4-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF-CBT(BO)) was subjected to GPC testing, and the number-average molecular weight M n = 40.53 kDa, and the polydispersity index (PDI) of the polymer is 2.05.

[0087] The synthetic route is as follows:

[0088]

[0089] Example 5

[0090] This example provides a method for preparing an A5-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF(BO)-CBT), which specifically includes:

[0091] BDTF(BO)-2Sn (105.2 mg, 0.1 mmol) and CBT-2Br (55.3 mg, 0.1 mmol) were added to a reaction flask equipped with a magnetic stirrer. Then the vial was transferred to a glove box protected by N2, where Pd2(dba)3 (9.25 mg, 0.008 mmol) and anhydrous chlorobenzene (7 mL) were added to obtain a mixture. The reaction mixture was sealed and heated at 110 °C for 6 hours. The mixture was cooled to room temperature and precipitated with 100 mL of methanol. Then the crude polymer was successively extracted with methanol, acetone, hexane, dichloromethane and chloroform until the extract was colorless. The chloroform solution was concentrated and precipitated in methanol. The precipitate was filtered and dried under vacuum to obtain 0.103 g of a dark solid polymer, namely A5-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (denoted as PBDTF(BO)-CBT).

[0092] The purified A5-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF(BO)-CBT) was subjected to GPC testing, and the number-average molecular weight M n = 21.23 kDa, and the polymer polydispersity (PDI) was 2.78.

[0093] The synthesis route is as follows:

[0094]

[0095] Example 6

[0096] This example provides a preparation method of A6-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF-CBT-T), which specifically includes:

[0097] BDTF-2Sn (94.1 mg, 0.1 mmol) and CBT-T-2Br (105.4 mg, 0.1 mmol) were added to a reaction flask equipped with a magnetic stirrer. Then the vial was transferred to a glove box protected by N2, where Pd2(dba)3 (9.25 mg, 0.008 mmol) and anhydrous chlorobenzene (7 mL) were added to obtain a mixture. The reaction mixture was sealed and heated at 110 °C for 6 hours. The mixture was cooled to room temperature and precipitated with 100 mL of methanol. Then the crude polymer was successively extracted with methanol, acetone, hexane, dichloromethane and chloroform until the extract was colorless. The chloroform solution was concentrated and precipitated in methanol. The precipitate was filtered and dried under vacuum to obtain 0.125 g of a dark solid polymer, namely A6-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (denoted as PBDTF-CBT-T).

[0098] The purified A6-benzo[1,2-b:4,5-b']dithiophene-fused benzothiadiazole-based conjugated polymer (PBDTF-CBT-T) was subjected to GPC testing, and the number-average molecular weight Mn = 11.51 kDa, and the polydispersity index (PDI) of the polymer is 2.15.

[0099] The synthetic route is as follows:

[0100]

[0101] To verify the performance of the benzodithiophene-fused benzothiadiazole-based conjugated polymer prepared, the polymer prepared in the example was subjected to ultraviolet-visible absorption testing, and the test results are as Figure 1 shown. The parameter changes are shown in Table 1. Among them: M n is the number-average molecular weight (unit: kDa, kilodalton), PDI is the polydispersity index (unitless), which is used to characterize the molecular weight and its distribution of the polymer; the LUMO (lowest unoccupied molecular orbital) and HOMO (highest occupied molecular orbital) energy levels, with the unit of electron volts (eV), reflect the electron gain and loss ability of the molecule, that is, the higher the HOMO energy level, the stronger the electron loss ability; the lower the LUMO energy level, the stronger the electron gain ability; λ max represents the maximum absorption wavelength of the polymer, λ onset represents the starting absorption wavelength, and the units of both are nanometers (nm), which are used to analyze the spectral characteristics; E g represents the energy gap (band gap), with the unit of electron volts (eV), which reflects the optoelectronic properties of the material; I 0-0 / I 0-1 is the ratio of the absorption intensities of two specific transitions, which is used to analyze the molecular energy level transition characteristics.

[0102] According to Figure 1 it can be seen that for the PBDT-CBT, PBDTF-CBT, PBDTCl-CBT, PBDTF-CBT(BO), PBDTF(BO)-CBT and PBDTF-CBT-T polymers in Examples 1-6, ultraviolet-visible absorption testing was carried out. Among them, a) is the polymer solution and b) is the thin film. During the process from the solution to the thin film, there is a red shift phenomenon for all the polymers. The red shift of PBDT-CBT is 4 nm; the red shifts of PBDTF-CBT, PBDTCl-CBT, PBDTF-CBT(BO) and PBDTF(BO)-CBT are all 3 nm; while the red shift phenomenon of PBDTF-CBT-T is the most obvious, reaching 10 nm, indicating that during the process from the solution to the thin film, the aggregation behavior change of PBDTF-CBT-T is the most obvious. The absorption edges (λ onset ) of the PBDT-CBT, PBDTF-CBT, PBDTCl-CBT, PBDTF-CBT(BO), PBDTF(BO)-CBT and PBDTF-CBT-T thin films are 649, 640, 640, 633, 640 and 674 nm respectively. The E g= 1240 / λ onset , the corresponding optical band gaps (E g ) are 1.91, 1.94, 1.94, 1.96, 1.94, and 1.84 eV, respectively. It can be seen that the absorption ranges and band gaps of PBDT-CBT, PBDTF-CBT, PBDTCl-CBT, PBDTF-CBT(BO), and PBDTF(BO)-CBT are not very different. However, the maximum absorption peak of PBDTF-CBT-T is blue-shifted by nearly 40 nm, and the absorption edge is red-shifted by nearly 40 nm, broadening the absorption range of the polymer, and the corresponding optical band gap is narrowed by nearly 0.1 eV, indicating that the introduction of thiophene π-bridges in the polymer has a great impact on absorption. At the same time, the I 0-0 / I 0-1 ratios of PBDT-CBT, PBDTF-CBT, PBDTCl-CBT, PBDTF-CBT(BO), and PBDTF(BO)-CBT are much greater than 1, and the maximum of PBDTF-CBT(BO) reaches 1.48, indicating that these polymers all have strong J-aggregation and can absorb light of different wavelengths in sunlight more effectively, increasing the number of excitons generated; while the I 0-0 / I 0-1 ratio of PBDTF-CBT-T is less than 1, only 0.90, indicating weak aggregation.

[0103] Table 1 Molecular weights, optical properties, and energy levels of polymers

[0104] Name of the polymer <![CDATA[M n / PDI(kDa / -)]]> <![CDATA[λ max (nm)]]> <![CDATA[λ max / λ onset (nm)]]> <![CDATA[E g (eV)]]> <![CDATA[I 0-0 / I 0-1 > PBDT-CBT 14.64 / 1.75 604 608 / 649 1.91 1.33 PBDTF-CBT 18.05 / 2.26 600 603 / 640 1.94 1.25 PBDTCl-CBT 17.93 / 3.06 600 603 / 640 1.94 1.38 PBDTF-CBT(BO) 40.53 / 2.05 600 603 / 633 1.96 1.48 PBDTF(BO)-CBT 21.23 / 2.78 600 603 / 640 1.94 1.37 PBDTF-CBT-T 11.51 / 2.15 562 572 / 674 1.84 0.90

[0105] To study and test the photovoltaic performance of the polymers, binary bulk heterojunction (BHJ) OSCs were fabricated with a forward device structure of ITO / PEDOT:PSS / Polymers:Y6 / PDINO / Ag. The ITO-coated glass was ultrasonically stirred and cleaned successively in detergent, deionized water, acetone, and isopropyl alcohol, and then plasma-treated for 30 min. Then, PEDOT:PSS (Baytron PVP4083) was spin-coated on the ITO glass at a speed of 4000 rpm for 30 s and annealed in air at 150 °C for 20 min. These were transferred to a glove box filled with N2. The active layer solution (with a weight ratio of Polymers:Y6 of 1:1.2) was prepared in chlorobenzene, and the total active layer solution concentration was 16.0 mg / mL, containing 0.5% CN. The active layer solution was stirred at 40 °C for 3 h, and then after the solution cooled to room temperature, the active layer was spin-coated on the substrate at a spin-coating speed of 3000 rpm. The thermal annealing of the blend film was at 110 °C for 10 min. Finally, PDINO dissolved in methanol was spin-coated on the top of the active layer at a concentration of 3 mg / mL. By at 10 -7Device fabrication is completed by depositing 100 nm of silver in a vacuum chamber of Torr. However, the device structure in actual applications is not limited to this.

[0106] The device area of the battery is 0.04 mm 2 , which is defined by a metal mask with the aperture aligned with the device area. The corresponding photovoltaic parameters are summarized in Table 2, where V OC represents the open-circuit voltage, that is, the voltage of the device when no load is connected under illumination, reflecting the charge separation ability of the device; J SC represents the short-circuit current density, that is, the current density when the device is short-circuited (voltage is zero), reflecting the collection ability of photo-generated carriers; FF represents the fill factor, which measures the power output characteristics of the device and reflects the degree of approximation of the actual power curve to an ideal rectangle; PCE represents the photoelectric conversion efficiency, that is, the efficiency of converting light energy into electrical energy, which is a key indicator of the comprehensive performance of the device. According to the formula PCE = (V oc × J sc × FF) / P in , P in is the incident light power density.

[0107] Table 2 Photovoltaic device performance of the forward device structure

[0108] Polymer <![CDATA[V OC (V)]]> <![CDATA[J SC (mA·cm -2 )]]> FF (%) PCE (%) PBDT-CBT: Y6 0.80 23.90 63.65 12.20

[0109] As can be seen from Table 2, applying the polymer prepared in the examples of this application to the forward device structure shows good device performance, with a PCE of 12.20%, indicating that the polymer prepared in this application has relatively excellent photoelectrochemical properties and has broad application prospects in organic photovoltaic devices.

[0110] Therefore, the benzodithiophene-fused benzothiadiazole-based conjugated polymer provided in this application realizes the combination of wide-spectrum absorption and efficient carrier transport through the synergistic design of a novel benzothiadiazole conjugated unit and a π-bridge structure; the alkyl chain modification strategy significantly improves the solubility and molecular weight distribution of the material, laying a foundation for the preparation of high-quality active layer films. The preparation method provided in this application obtains a target product with regular structure and stable performance by precisely controlling the monomer molar ratio, reaction temperature, and purification process. Experimental results show that when this conjugated polymer is applied to a forward device, the photoelectric conversion efficiency can reach up to 12.20%, showing broad application prospects in the field of organic photovoltaic cells, effectively solving the deficiencies of existing conjugated polymers in spectral matching, processing performance, and photoelectric conversion efficiency, as well as the problem of narrow selection range.

[0111] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments.

[0112] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limiting the present application; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A benzodithiophene-fused benzothiadiazole-based conjugated polymer, characterized in that, Having the chemical structural formula shown in Formula I or Formula II: In Formula I, R1 and R2 are each independently selected from hydrogen, a linear or branched alkyl group having 1 - C 20 , a cycloalkyl group having 6 - C 20 , a linear or branched alkoxy group having 1 - C 20 , or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; n is a natural number from 10 to 1000; In Formula II, R1 and R2 are independently selected from one of hydrogen, a linear or branched alkyl group having C1-C 20 , a cycloalkyl group having C6-C 20 , a linear or branched alkoxy group having C1-C 20 , and an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; the π-bridge is selected from one of thiophene, thiophene with an alkyl chain, thiophene with a halogen element, thiophene containing both an alkyl chain and a halogen, benzene, benzene with an alkyl chain, benzene with a halogen element, benzene containing both an alkyl chain and a halogen, and a biphenyl linking unit; n is a natural number from 10 to 1000.

2. The benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 1, wherein In Formula I, R1 and R2 are each independently selected from straight-chain or branched-chain alkyl groups having 1 to 20 carbon atoms; In Formula II, R1 and R2 are each independently selected from straight-chain or branched-chain alkyl groups having 1 to 20 carbon atoms.

3. The benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 1, wherein The number average molecular weight of the benzodithiophene-fused benzothiadiazole-based conjugated polymer is 11 - 45 kDa, and the dispersion coefficient is 1.75 - 3.

06.

4. A method for preparing a benzodithiophene-fused benzothiadiazole-based conjugated polymer according to any one of claims 1-3, characterized in that, The preparation method includes: Providing Compound A and Compound B; Under an inert gas atmosphere and in the presence of a catalyst, carrying out a Stille coupling reaction on the Compound A and Compound B in an organic solvent, and separating and purifying to obtain the benzodithiophene-fused benzothiadiazole-based conjugated polymer; Compound A has the chemical structural formula shown in Formula III: In formula III, R1 is selected from one of hydrogen, a linear or branched alkyl group having C1-C 20 , a cycloalkyl group having C6-C 20 , a linear or branched alkoxy group having C1-C 20 , or an aryl group containing one or more aromatic rings; X is one of hydrogen, fluorine, chlorine, bromine, and iodine; Compound B has the chemical structural formula shown in Formula IV or Formula V: In Formula IV or Formula V, R2 is selected from one of hydrogen, a linear or branched alkyl group having C1-C 20 , a cycloalkyl group having C6-C 20 , a linear or branched alkoxy group having C1-C 20 , and an aryl group containing one or more aromatic rings; the π-bridge is selected from one of thiophene, alkyl chain-containing thiophene, halogen element-containing thiophene, thiophene containing both an alkyl chain and a halogen, benzene, alkyl chain-containing benzene, halogen element-containing benzene, benzene containing both an alkyl chain and a halogen, and a biphenyl linking unit.

5. The preparation method of the benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 4, characterized in that, The molar ratio of the Compound A and Compound B is 1:

1.

6. The preparation method of the benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 4, characterized in that, When carrying out the Stille coupling reaction, the reaction temperature is 100 - 120 °C, and the reaction time is 6 hours.

7. The preparation method of the benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 4, wherein The catalyst is one or more of tris(dibenzylideneacetone)dipalladium, bis(triphenylphosphine)palladium dichloride, or tetrakis(triphenylphosphine)palladium.

8. The preparation method of the benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 4, wherein, The organic solvent is one or more of tetrahydrofuran, ethylene glycol dimethyl ether, benzene, and toluene.

9. The preparation method of the benzodithiophene-fused benzothiadiazole-based conjugated polymer according to claim 4, characterized in that, The operation of separation and purification is: cooling the mixture to room temperature and precipitating with 100 ml of methanol, extracting successively with methanol, acetone, hexane, dichloromethane, and chloroform until the extract is colorless, then concentrating with methanol and vacuum filtering to obtain the benzodithiophene-fused benzothiadiazole-based conjugated polymer.

10. Use of the benzodithiophene-fused benzothiadiazole-based conjugated polymer according to any one of claims 1 - 3 or the benzodithiophene-fused benzothiadiazole-based conjugated polymer prepared by the preparation method according to any one of claims 4 - 9 in the preparation of an organic photovoltaic cell device.

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