Preparation of fluorene-benzothiadiazole multi-chain bola liquid crystal compound and modification of fluorene-benzothiadiazole multi-chain bola liquid crystal compound on silicon-based solar cell

Abstract

The invention provides two fluorene-benzothiadiazole multi-chain type bola liquid crystal compounds, a preparation method thereof and application of the fluorene-benzothiadiazole multi-chain type bola liquid crystal compounds in solar cells. Relates to the fields of liquid crystal materials and organic solar cells. The two types of molecules contain bifunctional functional groups of fluorene and benzothiadiazole at the same time, and can be self-assembled to form complex honeycomb columnar phase and cubic phase liquid crystals by adjusting the lengths of conjugated linking groups and alkyl side chains. Fn of a short side chain forms a triangular honeycomb hexagonal columnar liquid crystal (Cohex / p6mm), F18 of a long side chain observes a network cubic intermediate phase Cub / pm3n in a high-temperature interval, and the F18 of the long side chain is a Cohex / p6mm liquid crystal phase at a low temperature. The TFn of the short side chain can also form a Cohex / p6mm liquid crystal phase, the TF18 of the long side chain can form a square honeycomb columnar liquid crystal Colsq / P4gm at a low temperature, and the Cohex / p6mm liquid crystal is formed at a high temperature. In addition, the PEDOT: PSS thin film is induced to be modified by utilizing the self-assembly property of the compounds Fn and TFn, and a PEDOT: PSS / n-Si heterojunction solar cell device with high efficiency and strong practicability is prepared. The material is expected to be widely applied in the field of organic photoelectric materials.

Description

Technical Field

[0001] The present invention relates to the field of fluorene-benzothiadiazole multi-chain BOLA liquid crystal materials, namely, a preparation method of BOLA liquid crystal compounds based on fluorene and benzothiadiazole (BTD) derivatives and their application in organic / n-Si heterojunction solar cells. Such compounds are expected to be widely used in the field of organic optoelectronics. Background Art

[0002] Liquid crystal systems are a perfect example of how nature can form well-defined structures through the self-assembly of soft matter. A particularly successful example is the multichain BOLA amphiphilic block molecules. These molecules consist of a π-conjugated rod-shaped aromatic core with glycerol end groups at both ends and flexible side chains. Depending on the length of the conjugated core rod and the number and length of the side chains, these molecules can self-assemble to form liquid crystal phases with complex honeycomb structures. In the honeycomb structure, the π-conjugated rod-shaped aromatic cores are connected by a hydrogen bond network formed by the glycerol end groups, and the resulting prismatic units are filled with flexible side chains with the π-conjugated rod-shaped aromatic cores perpendicular to the long axis of the column. Depending on the volume of the side chains and the length of the rigid rod-shaped core, different types of honeycomb phases are observed, such as triangles, squares, pentagons, and hexagons.

[0003] The present invention focuses on fluorene and benzothiadiazole because these units have been shown to be a class of organic optoelectronic materials with excellent properties. In particular, fluorene derivatives are known for their strong blue fluorescence emission and high thermal stability. 9-9 dialkylfluorene has been used as a π-conjugated linker to avoid molecular aggregation and inhibit charge recombination. Due to the sp 3 Hybridization, the two alkyl chains are almost perpendicular to the conjugated backbone, and the central fluorene unit usually distorts the π-conjugated coplanarity of the molecule. In this regard, it is of great significance to find a way to assemble such π-conjugated aromatic compounds into complex liquid crystals. In particular, the self-healing ability of liquid crystals makes fluorene derivatives of great value as organic optoelectronic materials. Liquid crystal derivatives of fluorene form smectic and nematic liquid crystals in most cases, with only rare cases of multi-chain fluorene forming triangular honeycomb columnar phases. However, multi-chain BOLA liquid crystals containing both fluorene and benzothiadiazole dual functional groups have not been reported. Therefore, it is extremely important to expand the appearance of more complex honeycomb liquid crystals in such derivatives and enrich the types of BOLA-type compound liquid crystal libraries.

[0004] Organic / n-Si heterojunctions consisting of silicon-based absorbers and organic carrier-selective functional layers are an effective approach to fabricate next-generation photovoltaic cells with low cost and high power conversion efficiency (PCE) due to their many unique properties of n-Si and simple device structure. Nevertheless, organic semiconductors associated with non-ideal interfacial contacts and low electrical conductivity greatly hinder the improvement of device performance of planar heterojunction solar cells. Among them, a feasible approach is to further improve device efficiency by controlling the interfacial contact and conductivity of organic semiconductors. Poly(3,4-ethylenedioxythiophene):polystyrene (PEDOT:PSS) polymers are considered to be one of the most promising candidates for hole-selective functional layers in organic and perovskite solar cells due to their high permeability and tunable optoelectronic properties. However, the conductivity of pure PEDOT:PSS (PH-1000) films is very low, making it difficult to use as carrier-selective and collection functional layers for transparent conductive electrodes in efficient organic / n-Si heterojunction solar cells. The short-circuit current and fill factor of PEDOT:PSS / n-Si heterojunction solar cells are lower than those of conventional homogeneous pn Si heterojunction solar cells. This means that the heterojunction's ability to separate photogenerated carriers is still weaker than that of conventional pn junctions. It is still very challenging to enhance electrical performance and energy level alignment. The present invention uses the self-assembly induction ability of liquid crystal molecules to modify the PEDOT:PSS thin film layer to improve the efficiency of organic / n-Si heterojunction solar cells, which is a novel and feasible solution. Summary of the invention

[0005] The present invention provides a method for preparing such fluorene-benzothiadiazole multi-chain BOLA liquid crystal compounds, introduces different conjugated groups into the BOLA amphiphilic molecules, and obtains more liquid crystal materials with complex honeycomb columns by adjusting the length of the C-9 side chain on the fluorene. Based on the self-assembly ability of the liquid crystal material, these BOLA liquid crystal compounds are doped into PEDOT:PSS / n-Si heterojunction solar cells, which significantly improves the photoelectric conversion efficiency of the device.

[0006] The multi-chain BOLA liquid crystal compound of the present invention is characterized in that the compound has the following structural formula: The compound is Fn, wherein n is 12, 16, or 18; The compound is TFn, wherein n is 12, 16, or 18.

[0007] The multi-chain BOLA liquid crystal compound is characterized in that the compound is prepared by the following steps: 1. Step 1: 2,7-dibromofluorene and bromoalkane (bromododecadecane) are dissolved in dry tetrahydrofuran, potassium tert-butoxide is added under ice bath, and the mixture is reacted at room temperature for 3 hours to obtain compound 1 / n; 2. Step 2: 1 / n and p-hydroxyphenylboronic acid are dissolved in tetrahydrofuran, and then a potassium carbonate solution dissolved in water is added to the tetrahydrofuran solution. Under nitrogen protection, after ultrasonic deoxygenation, a catalytic amount of tetrakis(triphenylphosphine)palladium is added, and the mixture is stirred and refluxed at 78° C. for 12 hours to obtain 2 / n; 3. Step 3: Dissolve the compound 2 / n obtained in step 2 in acetonitrile solution, add 2 equivalents of potassium carbonate, stir for 30 minutes, then add allyl bromide, react at 70° C. for 12 hours to obtain compound 3 / n; 4. Step 4: Dissolve 3 / n in acetone, then add a catalytic amount of N-methylmorpholine-N-oxide (NMMNO) and an appropriate amount of osmium tetroxide (OsO4), stir at 40°C for 3 hours to obtain 4 / n; 5. Step 5: Dissolve the compound 4 / n obtained in step 4 in tetrahydrofuran, add pyridinium p-toluenesulfonate (PPTS) and acetone dimethyl acetal, and react at room temperature for 12 hours to complete the protection of the terminal vicinal diol to obtain compound 5 / n; 6. Step 6: 5 / n and bis-pinacol borate were dissolved in 1,4-dioxane, followed by the addition of potassium acetate, and after ultrasonic deoxygenation under nitrogen protection, a catalytic amount of 1,1'-bis(diphenylphosphino)ferrocenepalladium dichloride was added, and the mixture was stirred at 100°C for 12 hours to obtain 6 / n; 7. Step 7: 6 / n and 4,7-dibromo-2,1,3-benzothiadiazole were dissolved in tetrahydrofuran, and then a potassium carbonate solution dissolved in water was added to the tetrahydrofuran solution. Under nitrogen protection, after ultrasonic deoxygenation, a catalytic amount of tetrakis(triphenylphosphine)palladium was added, and the mixture was stirred and refluxed at 78° C. for 18 hours. After the reaction was completed, the solvent was removed, and the crude product did not need to be purified, and was further directly dissolved in a mixed solution of tetrahydrofuran / methanol, and 10% HCl was added. After reacting at 70° C. for 3 hours, a yellow solid Fn series product was obtained; 8. Step 8: 6 / n and 4,4,7-di(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole are dissolved in tetrahydrofuran, and then a potassium carbonate solution dissolved in water is added to the tetrahydrofuran solution. Under nitrogen protection, after ultrasonic deoxygenation, a catalytic amount of tetrakis(triphenylphosphine)palladium is added, and the mixture is stirred and refluxed at 78° C. for 18 hours. After the reaction is completed, the solvent is removed, and the crude product does not need to be purified, and is further dissolved in a mixed solution of tetrahydrofuran / methanol, 10% HCl is added, and the mixture is reacted at 70° C. for 3 hours to obtain a red solid TFn series product.

[0008] in, Compound 1 / n is 1 / 12, 1 / 16, 1 / 18, which are 2,7-dibromo-9,9-didodecyl-9H-fluorene, 2,7-dibromo-9,9-dihexadecyl-9H-fluorene, 2,7-dibromo-9,9-dioctadecyl-9H-fluorene respectively; Compound 2 / n is 2 / 12, 2 / 16, 2 / 18, which are 4-(7-bromo-9,9-didodecyl-9H-fluoren-2-yl)phenol, 4-(7-bromo-9,9-dihexadecyl-9H-fluoren-2-yl)phenol, 4-(7-bromo-9,9-dioctadecyl-9H-fluoren-2-yl)phenol respectively; Compound 3 / n is 3 / 12, 3 / 16, 3 / 18, which are 2-(4-(allyloxy)phenyl)-7-bromo-9,9-didodecyl-9H-fluorene, 2-(4-(allyloxy)phenyl)-7-bromo-9,9-dihexadecyl-9H-fluorene, 4 2-(4-(allyloxy)phenyl)-7-bromo-9,9-dioctadecyl-9H-fluorene, respectively; Compound 4 / n are 4 / 12, 4 / 16, and 4 / 18, which are 3-(4-(7-bromo-9,9-didodecyl-9H-fluoren-2-yl))phenoxy)propane-1,2-diol, 3-(4-(7-bromo-9,9-dihexadecyl-9H-fluoren-2-yl))phenoxy)propane-1,2-diol, and 3-(4-(7-bromo-9,9-dioctadecyl-9H-fluoren-2-yl))phenoxy)propane-1,2-diol, respectively; Compound 5 / n is 5 / 12, 5 / 16, and 5 / 18, which are 4-((4-(7-bromo-9,9-didodecyl-9H-fluoren-2-yl))phenoxy)methyl)-2,2-dimethyl-1,3-dioxolane, 4-((4-(7-bromo-9,9-dihexadecyl-9H-fluoren-2-yl))phenoxy)methyl)-2,2-dimethyl-1,3-dioxolane, and 4-((4-(7-bromo-9,9-dioctadecyl-9H-fluoren-2-yl))phenoxy)methyl)-2,2-dimethyl-1,3-dioxolane; Compound 6 / n is 6 / 12, 6 / 16, and 6 / 18, which are 2-(7-(4-((2,2-dimethyl-1,3-dioxolan-4-yl))methoxy)phenyl)-9,9-didodecanyl-9H-fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 2-(7-(4-((2,2-dimethyl-1,3-dioxolan-4-yl))methoxy)phenyl)-9,9-dixadecanyl-9H-fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 2-(7-(4-((2,2-dimethyl-1,3-dioxolan-4-yl))methoxy)phenyl)-9,9-diodecyl-9H-fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, -fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.

[0009] In this new type of fluorene-benzothiadiazole multi-chain bola liquid crystal compounds, the molecules can self-assemble to form complex honeycomb columnar phases and cubic phases. For the Fn series, two different LC phases were observed. F12 and F16 with short side chains form triangular honeycomb hexagonal columnar liquid crystals (Col hex△ / p 6 mm ) and F18 with long alkyl side chains have cubic phase liquid crystal (Cub / pm 3 n ), forming triangular honeycomb hexagonal columnar liquid crystal in the low temperature range (Col hex△ / p 6 mm TF16 forms a triangular honeycomb hexagonal columnar liquid crystal (Col hex△ / p 6 mm ). The long-chain compound TF18 can form a square honeycomb columnar liquid crystal (Col squ / P 4 gm ), high temperature is still triangular honeycomb hexagonal columnar liquid crystal (Col hex△ / p 6 mm In addition, the self-assembly ability of compounds Fn and TFn was used to induce the modification of PEDOT:PSS thin films, and a high-efficiency and practical PEDOT:PSS / n-Si heterojunction solar cell device was prepared.

[0010] Instruction Manual Figure 1 The preparation route of the present invention; Figure 2 This is the columnar liquid crystal texture image of compound F12 observed under a polarizing microscope at 120°C; Figure 3 This is the columnar liquid crystal texture image of compound F16 observed under a polarizing microscope at 120°C; Figure 4 This is the columnar liquid crystal texture image of compound F18 observed under a polarizing microscope at 100°C; Figure 5 This is the columnar liquid crystal texture image of compound TF16 observed under a polarizing microscope at 120°C; Figure 6 This is the columnar liquid crystal texture image of compound TF18 observed under a polarizing microscope at 100°C; Figure 7 This is the columnar liquid crystal texture image of compound TF18 observed under a polarizing microscope at 130°C; Figure 8 is the XRD pattern of compound F16 at 120°C; Fig. 9 is the XRD pattern of compound F18 at 100 °C; Fig.10 is the XRD pattern of compound F18 at 130°C; Fig.11 is the XRD pattern of compound TF18 at 100°C; Fig.12 is the XRD pattern of compound TF18 at 130°C; Fig.13 The UV-visible absorption spectra of dichloromethane solutions and films of compounds F16 and TF16; Fig.14 The dichloromethane solution and film fluorescence emission spectra of compounds F16 and TF16; Fig.15 The JV current density voltage characteristic curve of solar cells with different dopants in PEDOT:PSS films; Fig.16 Device photo of the prepared PEDOT:PSS:dopant / n-Si heterojunction solar cell; Fig.17 The H-NMR spectrum characterization of compound F16; Fig.18 The NMR carbon spectrum characterization of compound F16; Fig.19 The H-NMR spectrum characterization of compound TF16; Fig. 20 This is the C NMR characterization of compound TF16. DETAILED DESCRIPTION

[0011] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0012] Example 1: Preparation and characterization of multi-chain bola liquid crystal compounds Fn and TFn according to Figure 1 The preparation route of is as follows: 1. Step 1, take an appropriate amount of 2,7-dibromofluorene (15 mmol) and dissolve it in tetrahydrofuran, add potassium tert-butoxide (30 mmol) under ice bath, stir for 30 minutes, add bromoalkane (31 mmol), return to room temperature, react for 3 hours, add 40 ml water to quench the reaction, extract with dichloromethane three times (30 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, remove the organic solvent by vacuum distillation, and recrystallize from ethanol. A white solid 1 / n is obtained, with a yield of 96%; The reaction formula is as follows: .

[0013] 2. Step 2, 1 / n (10 mmol) and p-hydroxyphenylboronic acid (10 mmol) were dissolved in 40 mL of tetrahydrofuran, and then 10 ml of an aqueous solution of potassium carbonate (20 mmol) was added thereto. Under N2 protection, the mixture was ultrasonically deoxygenated for 15 minutes, and a catalytic amount of tetrakistriphenylphosphine palladium was quickly added. The mixture was then refluxed at 78°C for 12 hours and monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and the mixture was extracted three times with dichloromethane (20 ml×3). The organic layers were combined and dried with anhydrous magnesium sulfate. The organic solvent was removed by distillation under reduced pressure. The crude product was purified by column chromatography. The eluent was petroleum ether: ethyl acetate 15:1. A colorless liquid 2 / n was obtained. The yield was 45%; The reaction formula is as follows: .

[0014] 3. Step 3, take an appropriate amount of 2 / n (4 mmol) and dissolve it in acetonitrile, add potassium carbonate (8 mmol), stir for 30 minutes, add allyl bromide (4.2 mmol), react at 70°C for 12 hours, add 20 ml of water to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and distill under reduced pressure to remove the organic solvent. The crude product is purified by column chromatography, the eluent is petroleum ether: ethyl acetate 15:1, and a colorless liquid 3 / n is obtained, with a yield of 80%; The reaction formula is as follows: .

[0015] 4. Step 4, take an appropriate amount of 3 / n (3 mmol) and dissolve it in acetone, add a catalytic amount of N-methylmorpholine oxide and osmium tetroxide (3.3 mmol), react at 40°C for 3 hours, add 20 ml of a saturated aqueous solution of sodium thiosulfate to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and distill under reduced pressure to remove the organic solvent. The crude product is purified by column chromatography, and the eluent is petroleum ether: dichloromethane 1:1 to obtain a colorless liquid 4 / n, with a yield of 93%; The reaction formula is as follows: .

[0016] 5. Step 5, take an appropriate amount of 4 / n (2.5 mmol) and dissolve it in dry tetrahydrofuran, add acetone dimethyl acetal (10 mmol) and a catalytic amount of pyridinium p-toluenesulfonate, react at room temperature for 12 hours, add 20 ml of water to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and distill under reduced pressure to remove the organic solvent. The crude product is purified by column chromatography, and the eluent is petroleum ether: dichloromethane 1:1 to obtain a colorless liquid 5 / n, with a yield of 75%; The reaction formula is as follows: .

[0017] 6. Step 6, take an appropriate amount of 5 / n (1.5 mmol) and bis-pinacol borate (3 mmol) and dissolve them in dry 1,4-dioxane, add potassium acetate (6 mmol), and deoxygenate by ultrasonication for 15 minutes under N2 protection, quickly add a catalytic amount of 1,1'-bis(diphenylphosphino)ferrocene]palladium dichloride, and then reflux at 100°C for 12 hours. Monitor the reaction with thin layer chromatography. After the reaction is completed, add 20 ml of water to the reaction system to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and remove the organic solvent by reduced pressure distillation. The crude product is purified by column chromatography, and the eluent is petroleum ether: dichloromethane 2:1 to obtain a white solid 6 / n, with a yield of 85%; The reaction formula is as follows: .

[0018] 7. Step 7, 6 / n (0.5 mmol) and 4,7-dibromo-2,1,3-benzothiadiazole (0.24 mmol) were dissolved in 20 ml of tetrahydrofuran solution, and then 5 ml of potassium carbonate (1 mmol) was added thereto. Under N2 protection, ultrasonic deoxygenation was performed for 15 minutes, and a catalytic amount of tetrakistriphenylphosphine palladium was quickly added. Then, the mixture was refluxed at 78°C for 18 hours and monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and then the mixture was extracted three times with dichloromethane (20 ml×3). The organic layers were combined and the organic solvent was removed by vacuum distillation to obtain a crude product. The crude product did not need to be purified, and was further dissolved in a 1:1 mixed solution of tetrahydrofuran: methanol, and 8 ml of 10% HCl solution was added. The mixture was reacted at 70°C for 3 hours and monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and the mixture was extracted three times with dichloromethane (20 ml×3). ml×3), the organic layers were combined, dried with anhydrous magnesium sulfate, and the organic solvent was removed by distillation under reduced pressure. The crude product was purified by column chromatography with the eluent being dichloromethane:methanol 10:1 to obtain yellow solid Fn series products with a yield of 79%-84%; The reaction formula is as follows: .

[0019] 8. Step 8, 6 / n (0.5 mmol) and 4,7-di(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole (0.24 mmol) were dissolved in 20 mL of tetrahydrofuran, and 5 ml of an aqueous solution of potassium carbonate (1 mmol) was added thereto. Under N2 protection, ultrasonic deoxygenation was performed for 15 minutes, and a catalytic amount of tetrakistriphenylphosphine palladium was quickly added. The mixture was refluxed at 78°C for 18 hours and monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and the mixture was extracted three times with dichloromethane (20 ml×3). The organic layers were combined and the organic solvent was removed by distillation under reduced pressure. The crude product did not need to be purified. The crude product was dissolved in a mixture of tetrahydrofuran and methanol in a ratio of 1:1, and 8 ml of 10% HCl solution was added. The mixture was reacted at 70°C for 3 hours and monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added and the mixture was extracted three times with dichloromethane (20 ml×3). The organic layers were combined and dried with anhydrous magnesium sulfate. The organic solvent was removed by vacuum distillation. The crude product was purified by column chromatography. The eluent was dichloromethane: methanol in a ratio of 10:1. Red solid TFn series products were obtained with a yield of 80%-83%. The reaction formula is as follows: .

[0020] All target compounds have similar NMR data, and representative compounds F16 and TF16 are selected to display their NMR data.

[0021] F16 NMR data such as Fig.17 , Fig.18 As shown: 1 H NMR (CDCl3, 400 MHz), δ (ppm): 7.90-7.89 (d, 2H, J = 2.80 Hz), 7.87(s, 2H), 7.82-7.80 (d, 8H, J = 8.00 Hz), 7.65-7.62(d, 2H, J = 8.40 Hz), 7.58 (d, 4H, J = 1.20 Hz), 7.55(s, 4H), 7.05-7.03 (d, 4H, J =8.80Hz), 4.18-4.16 (m, 2H), 4.14-4.12 (m, 4H), 3.92-3.88 (m, 2H), 3.83-3.79(m, 2H), 2.69 (s, 2H), 2.14-2.01 (m, 10 H), 1.62 (s, 4H), 1.28-1.10 (m, 99H), 0.86 (t, 21H). 13 C NMR (CDCl3; 100 MHz): 157.9, 154.4, 152.1, 151.4, 141.1,139.7, 139.5, 136.1, 135.0, 133.6, 128.3, 128.2, 127.9, 125.7, 123.9, 121.2,120.2, 119.7, 114.9, 77.3, 77.2, 77.0, 76.7, 70.4, 69.4, 63.7, 55.3, 40.4,31.9, 30.1, 29.6, 29.3, 29.3, 24.0, 22.7, 14.1; The NMR data of TF16 are as follows Fig.19 , Fig. 20 As shown: 1 H NMR (CDCl3, 400 MHz), δ (ppm): 8.16(s, 2H), 7.93 (s, 2H), 7.74-7.72 (d, 6H, J = 9.60 Hz), 7.68(s, 2H), 7.63-7.61(d, 4H, J = 8.80 Hz), 7.55-7.49 (m, 6H), 7.04-7.02 (d, 4H,J = 8.80Hz), 4.18-4.15(m, 2H), 4.13-4.11 (m, 4H), 3.91-3.88 (m, 2H), 3.82-3.78 (m, 2H), 2.70 (s,2H), 2.08-2.04 (m, 10 H), 1.63 (s, 4H), 1.27-1.07 (m, 98H), 0.87-0.73 (m, 22H). 13 C NMR (CDCl3; 100 MHz): 157.9, 152.7, 151.8, 151.7, 146.5, 140.8,139.7, 139.5, 138.3, 134.9, 132.8, 128.7, 128.3, 125.8, 125.7, 125.3, 124.9,123.9, 121.1, 120.1, 120.1, 120.0, 114.9, 77.3, 77.0, 76.8, 70.4, 69.4, 68.0,63.7, 55.4, 40.5, 31.9, 30.0, 29.7, 29.7, 29.7, 29.6, 29.4, 29.3, 25.6, 23.8,22.7, 14.1.

[0022] Example 2: Study on the optical properties of compounds Fn and TFn The optical properties of Fn and TFn prepared by the above steps are not affected by the length of the alkyl chain. Therefore, the medium-chain length compounds F16 and TF16 were selected to study their optical properties. -5 M) and the UV-visible absorption and fluorescence emission spectra of thin films were studied. Fig.13 As shown in Figure 14, the maximum absorption wavelength of compound F16 in dichloromethane solution is 333,424 nm, the maximum absorption wavelength in the thin film state is 340,436 nm, the maximum emission wavelength in dichloromethane solution is 551 nm, the maximum emission wavelength in the thin film state is 548 nm, and the fluorescence quantum yield is 62% and 85%, respectively. The maximum absorption wavelength of compound TF16 in dichloromethane solution is 309,370,514 nm, and the maximum absorption wavelength in the thin film state is 310,377,530 nm. It has a wide range of absorption (200-650 nm), which is more conducive to the application in solar cells. The maximum emission wavelength in dichloromethane solution is 650 nm, and the maximum emission wavelength in the thin film state is 675 nm, and the fluorescence quantum yield is 32% and 36%, respectively.

[0023] Example 3: Study on the liquid crystal properties of compounds Fn and TFn like Figure 2-12 As shown in Table 1, except for compound TF12 which is crystalline, the liquid crystal properties of the other compounds have been verified by polarizing microscope (POM), differential scanning calorimeter (DSC) and X-ray diffractometer (XRD). For the Fn series, two different LC phases were observed. Compounds F12 with the shortest alkyl chain and F16 with a medium chain length only form triangular honeycomb hexagonal columnar liquid crystals (Col hex△ / p 6 mm ). Long alkyl chain F18 has cubic phase liquid crystal (Cub / pm 3 n ), a triangular honeycomb hexagonal columnar liquid crystal is formed in the low temperature range (Col hex△ / p 6 mm ). Compound TF16 forms a triangular honeycomb hexagonal columnar liquid crystal (Col hex△ / p 6 mm ). The long-chain compound TF18 can form a square honeycomb columnar liquid crystal (Col squ / P 4 gm ), high temperature is still triangular honeycomb hexagonal columnar liquid crystal (Col hex△ / p 6 mm ).

[0024] Table 1: Phase transition temperature and lattice constant of compounds Fn and TFn Note: Cr: crystal; Col squ / p 4 gm : Tetragonal columnar phase; Col hex△ / P 6 mm : Hexagonal columnar phase; Cub / pm3n: with pm3 n Cubic phase of the crystal lattice; Iso: isotropic liquid. b Phase transition temperatures determined by POM.

[0025] Example 4: Preparation of high performance PEDOT:PSS / n-Si heterojunction solar cells like Fig.15 , 16As shown in the figure, a PEDOT:PSS / n-Si heterojunction solar cell was prepared, which consists of an Ag gate (200 nm), a PEDOT:PSS: liquid crystal compound film (about 110 nm thick), an n-type Si sheet (300 μm thick, resistivity 0.05~0.10 Ω·cm), and an aluminum (Al) electrode (100 nm). Table 2 shows the changes in the conductive properties of PEDOT:PSS (PH-1000) with the doping of F18 and TF18 in the PEDOT:PSS precursor solution film. With the addition of 1.1% F18, the conductivity of the PEDOT:PSS film increased significantly. The film conductivity increased from 77.11 to 207.90 S·cm -1 After adding 0.8% TF18, the conductivity of PEDOT:PSS film further increased to 268.92 S•cm -1 The carrier mobility also increases with the doping of F18 and TF18, from 5.68 to 6.18 and 10.70 cm 2 ·v -1 ·s -1 The carrier concentration of the film was improved by F18 and TF18 doping, from 8.5×10 19 Increased to 1.5×10 20 and 2.1×10 20 cm -3 , which is exactly the same as the trend of increasing film conductivity, confirming that the main reason for the increase in PEDOT:PSS film conductivity is the increase in the carrier concentration inside the film. Fig.15 The JV photovoltaic characteristics of different types of PEDOT:PSS / n-Si heterojunction solar cells under AM1.5G simulated sunlight are given. The results show that when the F18 doping concentration is 1.1 wt %, the short-circuit current density J SC From 31.16 mA•cm -2 Increased to 32.75 mA•cm -2 , the fill factor FF increased from 59.12% to 64.23%, and the open circuit voltage V OC The voltage increased from 0.649 V to 0.653 V, and the PCE increased to 13.74%. When 0.8 wt% TF18 was doped in the PEDOT:PSS solution, the device had the best performance, and the PCE increased to 14.50%.

[0026] Therefore, based on the preparation of PEDOT:PSS / Si heterojunction solar cell devices, PEDOT:PSS thin films were modified by doping bola liquid crystal compounds F18 and TF18 to prepare high-efficiency and practical PEDOT:PSS / n-Si heterojunction solar cell devices.

[0027] Table 2 Device performance parameters of PEDOT:PSS / n-Si heterojunction solar cells modified with different liquid crystal compounds Note: The selected doping concentrations of F18 and TF18 are already optimal.

[0028] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. The fluorene-benzothiadiazole multi-chain bola liquid crystal compound of the present invention is characterized in that This class of compounds has the following structural formula: Compound Fn, wherein n is 12, 16, or 18; Compound TFn, wherein n is 12, 16, or 18.

2. The fluorene-benzothiadiazole multi-chain bola liquid crystal compound according to claim 1 is characterized in that the aromatic core and the alkyl side chain in the structural formula are regulated to obtain two types of liquid crystal compounds Fn and TFn.

3. The fluorene-benzothiadiazole multi-chain bola liquid crystal compound according to claim 1, characterized in that It can be prepared by the following method: Step 1, take an appropriate amount of 2,7-dibromofluorene (15 mmol) and dissolve it in tetrahydrofuran, add potassium tert-butoxide (30 mmol) under ice bath, stir for 30 minutes, add bromoalkane (31 mmol), return to room temperature, react for 3 hours, add 40 ml water to quench the reaction, extract with dichloromethane three times (20 ml×3), remove the organic solvent by vacuum distillation, and recrystallize from ethanol. A white solid 1 / n is obtained, with a yield of 96%; . Step 2, 1 / n (10 mmol) and p-hydroxyphenylboronic acid (10 mmol) were dissolved in 40 ml tetrahydrofuran, and then 10 ml aqueous solution of potassium carbonate (20 mmol) was added thereto, and under N2 protection, ultrasonic deoxygenation was performed for 15 minutes, and a catalytic amount of tetrakistriphenylphosphine palladium was quickly added, and then refluxed at 78°C for 12 hours, and the reaction was monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and then extracted with dichloromethane three times (20 ml×3), the organic layers were combined, and the organic layers were dried with anhydrous magnesium sulfate. The organic solvent was removed by vacuum distillation, and the crude product was purified by column chromatography, and the eluent was petroleum ether: ethyl acetate 15:1, and a colorless liquid 2 / n was obtained, with a yield of 45%; Step 3, take an appropriate amount of 2 / n (4 mmol) and dissolve it in acetonitrile, add potassium carbonate (8 mmol), stir for 30 minutes, add allyl bromide (4.2 mmol), react at 70°C for 12 hours, add water to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and distill under reduced pressure to remove the organic solvent. The crude product is purified by column chromatography, and the eluent is petroleum ether: ethyl acetate 15:1 to obtain a colorless liquid 3 / n, with a yield of 80%; Step 4, take an appropriate amount of 3 / n (3 mmol) and dissolve it in acetone, add catalytic amounts of N-methylmorpholine oxide and osmium tetroxide (3.3 mmol), react at 40°C for 3 hours, then add 20 ml of saturated aqueous sodium thiosulfate to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and distill under reduced pressure to remove the organic solvent. The crude product is purified by column chromatography, and the eluent is petroleum ether: dichloromethane 1:1 to obtain colorless liquid 4 / n, with a yield of 93%; Step 5, take an appropriate amount of 4 / n (2.5 mmol) and dissolve it in dry tetrahydrofuran, add 2,2-dimethoxypropane (10 mmol) and a catalytic amount of pyridinium toluenesulfonate (PPTS), react at room temperature for 12 hours, add 20 ml of water to quench the reaction, and then extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and distill under reduced pressure to remove the organic solvent. The crude product is purified by column chromatography, and the eluent is petroleum ether: dichloromethane 1:1 to obtain a colorless liquid 5 / n, with a yield of 75%; Step 6, take an appropriate amount of 5 / n (1.5 mmol) and bis-pinacol borate (3 mmol) and dissolve them in dry 1,4-dioxane, add potassium acetate (6 mmol), and deoxygenate by ultrasonication for 15 minutes under N2 protection, quickly add a catalytic amount of 1,1'-bis(diphenylphosphino)ferrocene]palladium dichloride, and then reflux at 100°C for 12 hours. Monitor the reaction with thin layer chromatography. After the reaction is completed, add 20 ml of water to the reaction system, extract with dichloromethane three times (20 ml×3), combine the organic layers, dry the organic layers with anhydrous magnesium sulfate, and remove the organic solvent by vacuum distillation. The crude product is purified by column chromatography, and the eluent is petroleum ether: dichloromethane 2:1 to obtain a white solid 6 / n with a yield of 85%; Step 7, 6 / n (0.5 mmol) and 4,7-dibromo-2,1,3-benzothiadiazole (0.24 mmol) were dissolved in 20 ml of tetrahydrofuran solution, and then 5 ml of potassium carbonate (1 mmol) was added thereto. Under N2 protection, ultrasonic deoxygenation was performed for 15 minutes, and a catalytic amount of tetrakistriphenylphosphine palladium was quickly added. Then, the reaction was refluxed at 78°C for 18 hours, and the reaction was monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and then extracted with dichloromethane three times (20 ml×3), the organic layers were combined, and the organic solvent was removed by vacuum distillation to obtain a crude product. The crude product did not need to be purified, and was further dissolved in a mixed solution of tetrahydrofuran / methanol, and 8 ml of 10% HCl was added. The reaction was performed at 70°C for 3 hours, and the reaction was monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system. ml water, extracted with dichloromethane three times (20ml×3), combined the organic layers, dried with anhydrous magnesium sulfate, and distilled under reduced pressure to remove the organic solvent. The crude product was purified by column chromatography, with the eluent being dichloromethane:methanol 10:1, to obtain yellow solid Fn series products with a yield of 79%-84%; Step 8, 6 / n (0.5 mmol) and 4,7-di(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole (0.24 mmol) were dissolved in 20 ml of tetrahydrofuran, and 5 ml of an aqueous solution of potassium carbonate (1 mmol) was added thereto. Under N2 protection, the mixture was ultrasonically deoxygenated for 15 minutes, and a catalytic amount of tetrakistriphenylphosphine palladium was quickly added. The mixture was then refluxed at 78°C for 18 hours and monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added to the reaction system, and the mixture was extracted three times with dichloromethane (20 ml×3). The organic layers were combined and the organic solvent was removed by vacuum distillation. The crude product did not need to be purified. The crude product was dissolved in a tetrahydrofuran / methanol mixed solution, 8 ml of 10% HCl was added, and the reaction was carried out at 70°C for 3 hours. The reaction was monitored by thin layer chromatography. After the reaction was completed, 20 ml of water was added, and the mixture was extracted three times with dichloromethane (20 ml×3). The organic layers were combined and dried with anhydrous magnesium sulfate. The organic solvent was removed by vacuum distillation. The crude product was purified by column chromatography. The eluent was dichloromethane: methanol 10:

1. Red solid TFn series products were obtained. The yield was 80%-83%. . in, Compound 1 / n is 1 / 12, 1 / 16, 1 / 18, which are 2,7-dibromo-9,9-didodecyl-9H-fluorene, 2,7-dibromo-9,9-dihexadecyl-9H-fluorene, 2,7-dibromo-9,9-dioctadecyl-9H-fluorene respectively; Compound 2 / n is 2 / 12, 2 / 16, and 2 / 18, which are 4-(7-bromo-9,9-didodecyl-9H-fluoren-2-yl)phenol, 4-(7-bromo-9,9-dihexadecyl-9H-fluoren-2-yl)phenol, and 4-(7-bromo-9,9-dioctadecyl-9H-fluoren-2-yl)phenol, respectively; Compound 3 / n is 3 / 12, 3 / 16, and 3 / 18, which are 2-(4-(allyloxy)phenyl)-7-bromo-9,9-didodecyl-9H-fluorene, 2-(4-(allyloxy)phenyl)-7-bromo-9,9-dihexadecyl-9H-fluorene, and 2-(4-(allyloxy)phenyl)-7-bromo-9,9-dioctadecyl-9H-fluorene, respectively; Compound 4 / n is 4 / 12, 4 / 16, and 4 / 18, which are 3-(4-(7-bromo-9,9-didodecyl-9H-fluoren-2-yl))phenoxy)propane-1,2-diol, 3-(4-(7-bromo-9,9-dihexadecyl-9H-fluoren-2-yl))phenoxy)propane-1,2-diol, and 3-(4-(7-bromo-9,9-dioctadecyl-9H-fluoren-2-yl))phenoxy)propane-1,2-diol, respectively; Compound 5 / n is 5 / 12, 5 / 16, and 5 / 18, respectively, 4-((4-(7-bromo-9,9-didodecyl-9H-fluoren-2-yl))phenoxy)methyl)-2,2-dimethyl-1,3-dioxolane, 4-((4-(7-bromo-9,9-dihexadecyl-9H-fluoren-2-yl))phenoxy)methyl)-2,2-dimethyl-1,3-dioxolane, 4-((4-(7-bromo-9,9-dioctadecyl-9H-fluoren-2-yl))phenoxy)methyl)-2,2-dimethyl-1,3-dioxolane; Compound 6 / n is 6 / 12, 6 / 16, and 6 / 18, respectively, which are 2-(7-(4-((2,2-dimethyl-1,3-dioxolan-4-yl))methoxy)phenyl)-9,9-didodecanyl-9H-fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 2-(7-(4-((2,2-dimethyl-1,3-dioxolan-4-yl))methoxy)phenyl)-9,9-dixadecanyl-9H-fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, 2-(7-(4-((2,2-dimethyl-1,3-dioxolan-4-yl))methoxy)phenyl)-9,9-diodecyl-9H-fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, -fluorene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.

4. Use of the fluorene-benzothiadiazole multi-chain bola liquid crystal compound according to claims 1 and 2 as an organic liquid crystal material.

5. Use of the fluorene-benzothiadiazole multi-chain bola liquid crystal compound according to claims 1 and 2 for improving the photoelectric conversion efficiency of PEDOT:PSS / n-Si heterojunction solar cells.

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