An asymmetric donor material with different fluorine contents, its preparation method and application

Abstract

The present invention relates to the technical field of organic optoelectronic materials, in particular to an asymmetric donor material with different fluorine contents, its preparation method and application, including an organic small molecule donor material with an asymmetric two-dimensional side chain containing different fluorine atoms, abbreviated as Z-2F, whose structural formula is shown in Formula 1, and the preparation method of the donor material; the application of the donor material in the preparation of the following functional energy devices also belongs to the protection scope of the present invention: solar cells, organic light-emitting diodes and flexible display fields, including applications in the field of floating photovoltaics. The small molecule donor material containing fluorine atoms designed in the present invention forms an appropriate energy level difference with the acceptor material L8-BO, which is beneficial to exciton dissociation, and has better photovoltaic performance and a wider range of floating photovoltaic applications in the testing of organic solar cells.

Description

Technical Field

[0001] The present invention relates to the technical field of organic optoelectronic materials, and particularly to an asymmetric donor material with different fluorine contents, its preparation method and application. Background Art

[0002] When designing organic optoelectronic materials, halogen atoms such as fluorine (F) and chlorine (Cl) play important roles in improving material properties and expanding their functions due to their unique electronic properties: such as increasing material stability and improving charge transport ability, regulating optical absorption and emission characteristics, etc.

[0003] As a supplement to silicon solar cells, organic solar cells have great application potential in aspects such as floating solar on water, indoor photovoltaics, photovoltaic agriculture, and photovoltaic new energy vehicles. By introducing asymmetric side chains into all-small-molecule donors, a highly efficient small-molecule donor Z-2F was obtained, and by adding fluorine atoms to the benzene ring, the structure of the compound was finely tuned, reducing the HOMO energy level, increasing the intermolecular interaction force, enabling better miscibility between the donor and acceptor, and the highest efficiency of the device reached 17.9%, which is one of the highest values for floating organic solar devices on water currently.

[0004] Therefore, when developing new organic optoelectronic materials, reasonably selecting and introducing fluorine or chlorine atoms is a common strategy to optimize the optoelectronic properties of materials and meet the requirements of specific applications. However, the introduction of fluorine atoms also has its challenges, such as increased synthesis difficulty, increased cost, and environmental friendliness issues. At the same time, the environmental impact and sustainability issues brought about by the introduction of halogens also need to be considered. Summary of the Invention

[0005] The purpose of this application is to provide an asymmetric donor material with different fluorine contents, its preparation method and application, so that it has better photovoltaic performance and a wider range of applications in floating solar on water.

[0006] The embodiment of this application provides an asymmetric donor material with different fluorine contents, specifically an organic small-molecule donor material with an asymmetric two-dimensional side chain containing different fluorine atoms, and its structural formula is shown in Formula 1: Formula 1.

[0007] Furthermore, the preparation method of this asymmetric donor material with different fluorine contents specifically includes the following steps:

[0008] S1: Using tetrahydrofuran as the solvent and iodine as the initiator, add magnesium powder, 4-bromo-1,2-difluorobenzene. Reflux the mixture at 70 °C for 4 h. Carry out the reflux reaction until the magnesium is completely consumed, and then naturally cool it to room temperature to obtain Grignard reagent 1. Drop Grignard reagent 1 into the toluene solution of benzo[1,2-b:4,5-b']dithiophene-4,8-dione, and stir at room temperature. At the same time, using tetrahydrofuran as the solvent and iodine as the initiator, add magnesium powder, 5-bromo-3-chloro-2-(2-hexyldiethyl)thiolane. Reflux the mixture at 70 °C for 2 h until the magnesium is completely consumed, and then naturally cool it to room temperature to obtain Grignard reagent 2. Then transfer the newly prepared Grignard reagent 2 to a dropping funnel and slowly drop it into the above-mentioned mixed solution containing Grignard reagent 1. Subsequently, stir the mixture at room temperature overnight. Then add stannous chloride (II) dihydrate dissolved in 10% (mass concentration) HCl at room temperature, and then continue to stir the obtained solution at 50 °C for 3 h. After completion, naturally cool it to room temperature and then pour the reactant into water to obtain compound 1;

[0009] S2: Under the protection of argon at -78 °C, dropwise add n-butyllithium solution to the tetrahydrofuran solution containing compound 1. After adding, stir the mixture at -78 °C for 1 h, then add compound 1, and continue to stir the mixture at -78 °C for 1 h. Naturally warm it to room temperature and react for 12 h. Subsequently, cool the mixture to room temperature and add the tin reagent solution; then stir it at 50 °C for another 3 h to form compound 2; the tin reagent solution is prepared by dissolving stannous chloride (II) dihydrate in 10% (mass concentration) HCl;

[0010] S3: Under the protection of argon, using tetrakis(triphenylphosphine)palladium as the catalyst and toluene as the solvent, reflux compound 2 and 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde at 110 °C for 8 to 10 h to carry out the Stille coupling reaction to obtain compound 3;

[0011] S4: Under the protection of argon, add compound 3, 3-hexylrhodanine and a base to the solvent chloroform, and carry out the Knoevenagel condensation reaction at 60 °C to connect the rhodanine capping group to obtain an organic small molecule donor material containing an asymmetric two-dimensional side chain, abbreviated as compound Z-2F.

[0012] Furthermore, the molar ratio of 5-bromo-3-chloro-2-(2-hexyldiethyl)thiolane, 4-bromo-1,2-difluorobenzene, and benzo[1,2-b:4,5-b']dithiophene-4,8-dione in S1 is 1:2:2.3, and the molar ratio of benzo[1,2-b:4,5-b']dithiophene-4,8-dione to the tin reagent is 1:5.

[0013] Further, the molar ratio of compound 1 to the tin reagent in S2 is 1:2.5; the molar ratio of n-butyllithium to compound 1 is 1:3.5.

[0014] Further, the optimal condition for the reflux reaction in S3 is to reflux at 110 °C for 9 h; the molar ratio of compound 2 to 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde in S3 is 1:15, and the dosage ratio of the catalyst to compound 3 is 20 mg:10.31 mmol.

[0015] Further, the reaction time of the condensation reaction in S4 is 24 h; the molar ratio of 3-hexylrhodanine to compound 3 in S4 is 15:1; the dosage ratio of the base to compound 3 is 1.5 mL:0.654 mmol.

[0016] Further, the application of asymmetric donor materials with different fluorine contents in the preparation of the following functional energy devices: solar cells, organic light-emitting diodes, and flexible displays.

[0017] Further, the solar cell includes a floating organic solar cell on water; the floating organic solar cell on water includes a battery panel made of Z-2F material and a floating structure on water.

[0018] The beneficial effects of the present invention are as follows: By introducing benzene rings and thiophenes into small molecule donor materials simultaneously, the present invention designs and synthesizes a new small molecule donor material using asymmetric two-dimensional side chains, achieving a photoelectric conversion efficiency of 17.9%, having important application prospects in binary all-small molecule organic solar cells, and providing a certain theoretical basis for ternary organic solar cells; the designed small molecule donor material containing fluorine atoms in the present invention forms an appropriate energy level difference with the acceptor material L8-BO, which is conducive to exciton dissociation, and has better photovoltaic performance and wider floating photovoltaic applications on water in the tests of organic solar cells. Description of the Drawings

[0019] Figure 1 1H NMR spectrum of compound 1 prepared by the present invention 1 H NMR spectrum.

[0020] Figure 2 1H NMR spectrum of compound 1 prepared by the present invention 13 C NMR spectrum.

[0021] Figure 3 1H NMR spectrum of compound 2 prepared by the present invention 1 H NMR spectrum.

[0022] Figure 41H NMR spectrum of Compound 2 prepared according to the present invention 13 1H NMR spectrum

[0023] Figure 5 1H NMR spectrum of Compound Z-2F prepared according to the present invention 1 1H NMR spectrum

[0024] Figure 6 13C NMR spectrum of Compound Z-2F prepared according to the present invention 13 13C NMR spectrum

[0025] Figure 7 Normalized UV-Vis absorption spectra of Compound Z-2F thin film, Z-2F solution and L8-BO thin film prepared according to the present invention

[0026] Figure 8 Cyclic voltammograms of Compound Z-2F, L8-BO, and Ferrocene prepared according to the present invention

[0027] Figure 9 Schematic diagram of the structure of the floating system

[0028] Figure 10 Flow structure diagram of the reaction compounds in each step of Example 1

[0029] In the figure:

[0030] 1. Floating structure; 2. PV panel; 3. Fixed bracket; 4. Hinge structure Detailed implementation mode

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention

[0032] A non-symmetric donor material with different fluorine contents, specifically an organic small molecule donor material with a non-symmetric two-dimensional side chain containing different fluorine atoms, and its structural formula is shown in Formula 1 Formula 1

[0033] The preparation method of the above-mentioned non-symmetric donor material with different fluorine contents specifically includes the following steps

[0034] S1: Using tetrahydrofuran as the solvent and iodine as the initiator, add magnesium powder, 4-bromo-1,2-difluorobenzene. Reflux the mixture at 70 °C for 4 h until the magnesium is completely consumed, and then naturally cool it to room temperature to obtain Grignard reagent 1. Drop Grignard reagent 1 into the toluene solution of benzo[1,2-b:4,5-b']dithiophene-4,8-dione and stir at room temperature. Meanwhile, using tetrahydrofuran as the solvent and iodine as the initiator, add magnesium powder, 5-bromo-3-chloro-2-(2-hexyldiethyl)thiolane. Reflux the mixture at 70 °C for 2 h until the magnesium is completely consumed, and then naturally cool it to room temperature to obtain Grignard reagent 2. Then transfer the newly prepared Grignard reagent 2 to a dropping funnel and slowly drop it into the above-mentioned mixed solution containing Grignard reagent 1. Subsequently, stir the mixture at room temperature overnight. Then add stannous chloride (II) dihydrate dissolved in 10% (mass concentration) HCl at room temperature, and then continue to stir the resulting solution at 50 °C for 3 h. After completion, naturally cool it to room temperature and pour the reactant into water to obtain compound 1;

[0035] S2: Under the protection of argon at -78 °C, dropwise add n-butyllithium solution to the tetrahydrofuran solution containing compound 1. After addition, stir the mixture at -78 °C for 1 h, then add compound 1, and continue to stir the mixture at -78 °C for 1 h. Naturally warm it to room temperature and react for 12 h. Subsequently, cool the mixture to room temperature and add the tin reagent solution. Then stir it at 50 °C for another 3 h to form compound 2; the tin reagent solution is prepared by dissolving stannous chloride (II) dihydrate in 10% (mass concentration) HCl;

[0036] S3: Under the protection of argon, using tetrakis(triphenylphosphine)palladium as the catalyst and toluene as the solvent, reflux compound 2 and 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde at 110 °C for 8 to 10 h to carry out the Stille coupling reaction to obtain compound 3;

[0037] S4: Under the protection of argon, add compound 3, 3-hexylrhodanine and a base (the base is preferably piperidine) to the solvent chloroform, and carry out the Knoevenagel condensation reaction at 60 °C to connect the rhodanine capping group to obtain an organic small molecule donor material containing an asymmetric two-dimensional side chain, abbreviated as compound Z-2F.

[0038] The molar ratio of 5-bromo-3-chloro-2-(2-hexyldiethyl)thiolane, 4-bromo-1,2-difluorobenzene, and benzo[1,2-b:4,5-b']dithiophene-4,8-dione in S1 is 1:2:2.3, and the molar ratio of benzo[1,2-b:4,5-b']dithiophene-4,8-dione to the tin reagent is 1:5.

[0039] In S2, the molar ratio of compound 1 to the tin reagent is 1:2.5; the molar ratio of n-butyllithium to compound 1 is 1:3.5.

[0040] In S3, the optimal conditions for the reflux reaction are refluxing at 110 °C for 9 h; in S3, the molar ratio of compound 2 to 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde is 1:15, and the dosage ratio of the catalyst to compound 3 is 20 mg:10.31 mmol.

[0041] In S4, the reaction time of the condensation reaction is 24 h; in S4, the molar ratio of 3-hexylrhodanine to compound 3 is 15:1; the dosage ratio of the base to compound 3 is 1.5 mL:0.654 mmol.

[0042] Example 1: Synthesis of compound Z-2F, the process is as Figure 10 shown.

[0043] (1) Synthesis of compound 1:

[0044] 4-Bromo-1,2-difluorobenzene (52.11 mmol) and magnesium powder (62.53 mmol) were added to a round-bottom flask containing freshly distilled tetrahydrofuran (50 mL). Subsequently, iodine (20 mg) was added to the round-bottom flask as an initiator. The mixture was refluxed at 70 °C for 4 h until the magnesium was completely consumed. After the reaction was naturally cooled to room temperature (25 °C, the same below), Grignard reagent 1 was obtained. Then the newly prepared Grignard reagent 1 was transferred to a dropping funnel and slowly added dropwise (30 drops per minute) to a toluene solution containing benzo[1,2-b:4,5-b']dithiophene-4,8-dione (46.51 mmol) in 150 mL. Subsequently, 5-bromo-3-chloro-2-(2-hexyldecyl)thiophene (23.91 mmol) and magnesium powder (28.69 mmol) were added to a round-bottom flask containing freshly distilled tetrahydrofuran (50 mL). Subsequently, iodine (20 mg) was added to the round-bottom flask as an initiator. The mixture was refluxed at 70 °C for 2 h until the magnesium was completely consumed. After the reaction was naturally cooled to room temperature (25 °C, the same below), Grignard reagent 2 was obtained. Then the newly prepared Grignard reagent 2 was transferred to a dropping funnel and slowly added dropwise to the above mixed solution (30 drops per minute). Subsequently, the mixture was stirred overnight at room temperature. Then, tin(II) chloride dihydrate (260.55 mmol) dissolved in 10% (mass concentration) HCl (15 mL) was added. Then the resulting solution was continuously stirred at 50 °C for 3 h. After completion, the reaction mixture was poured into water after being naturally cooled to room temperature. The obtained organic phase was extracted with dichloromethane three times and then dried over anhydrous sodium sulfate. After removing the solvent by a rotary evaporator, the crude product was purified by silica gel column chromatography (eluent: petroleum ether) to obtain a light white solid - Compound 1 (yield 63%), namely 4-(4-chloro-5-(2-hexyldecyl)thiophen-2-yl)-8-(3,4-difluorophenyl)benzo[1,2-b:4,5-b']dithiophene, the 1 1H NMR spectrum is shown in Figure 1 .

[0045] (2) Synthesis of Compound 2

[0046] Under argon protection and at -78 °C, n-butyllithium (54.53 mmol, 1.6 M) was added dropwise (30 drops per minute) to a tetrahydrofuran solution (60 mL) of compound 1 (15.58 mmol). After the addition, the mixture was stirred at -78 °C for 1 h. Then, a tetrahydrofuran solution of trimethyltin chloride (38.95 mmol, 1 M) was added, and the mixture was stirred again at -78 °C for 1 h. Then, the temperature was allowed to rise to room temperature naturally. After stirring at room temperature for 12 h, the solution was poured into deionized water and extracted three times with anhydrous diethyl ether (50 mL each time), and then dried over anhydrous sodium sulfate. After removing the solvent with a rotary evaporator, the crude product was recrystallized twice from toluene (the recrystallization procedure was as follows: 50 mL of toluene was added to the crude product, and the product was dissolved by heating to 55 - 60 °C. After dissolution, the heating was turned off, and the solution was allowed to cool to room temperature naturally and left standing for 5 h. The precipitated crystalline product was filtered, and the same procedure was repeated for the second recrystallization), to obtain yellow solid compound 2 (yield of this step: 80%), whose 1 1H NMR is shown in Figure 2 .

[0047] (3) Synthesis of compound 3

[0048] Under argon protection, compound 2 (10.31 mmol), 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde (154.65 mmol) and tetrakis(triphenylphosphine)palladium (20 mg) were added to a round-bottom flask. Then, anhydrous toluene (30 mL) was added thereto, and the mixture was stirred at 110 °C for 9 h. After cooling to room temperature naturally, the reaction was quenched with deionized water. The resulting organic matter was extracted 3 times with dichloromethane (50 mL each time), and then anhydrous sodium sulfate was added for drying. After removing the solvent with a rotary evaporator, the crude product was purified by silica gel column chromatography (eluent: dichloromethane) to obtain red solid compound 3 (yield of this step: 48%).

[0049] (4) Synthesis of compound Z-2F

[0050] Under argon protection, compound 3 (0.654 mmol), 3-hexylrhodanine (9.81 mmol) and 0.1 mL of piperidine were dissolved in dry chloroform (15 mL). The above mixed solution was stirred at 60 °C for 24 h. After cooling to room temperature naturally, the reaction was quenched with deionized water and extracted three times with chloroform (50 mL each time). After removing the solvent with a rotary evaporator, the crude product was purified by column chromatography on silica gel (eluent: petroleum ether and chloroform with a volume ratio of 1:1) to obtain red solid compound Z-2F (yield of this step: 65%), namely the desired organic small molecule donor material compound Z-2F containing two fluorine atoms, whose 1 1H NMR spectrum is shown in Figure 4 .

[0051] Applications of asymmetric donor materials with different fluorine contents in the fields of solar cells, organic light-emitting diodes and flexible displays.

[0052] Taking the application of the present invention in solar cells as an example, the specific implementation manner is shown in Example 2.

[0053] Example 2: Preparation and Characterization of Organic Solar Cell Devices

[0054] Prepare an organic photovoltaic device: adopt the standard structure of ITO / anode interface layer / active layer / electron transport layer / top electrode.

[0055] (1) Substrate preparation: Ultrasonically treat the finished ITO glass (indium tin oxide conductive glass) substrate with a cleaner, deionized water, acetone and isopropanol, clean for 11 minutes in each step, and dry with a nitrogen gas stream.

[0056] (2) Spin-coat the anode interface layer: After ultrasonic cleaning, the ITO glass (indium tin oxide conductive glass) is treated with oxygen-Plasma. First, spin-coat PEDOT:PSS poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid (a mixed solution with a ratio of 1:1, pre-formulated when purchased) on ITO at 5000 rpm, and the annealing conditions are 150 °C for 15 min to obtain a surface film thickness of about 40 nm.

[0057] (3) Preparation of the active layer: Use the small molecule compound Z-2F and the compound BTR-Cl prepared in Examples 1 and 2 as donor materials and mix them with the acceptor L8-BO, add a mixed solvent of diiodomethane-chloroform (the volume ratio of diiodomethane to chloroform is 0.3 μL:100 μL) to prepare a blend solution (the total concentration of the donor and the acceptor is 20 mg / mL, and the mass ratio of the donor to the acceptor is 1.2:1). Spin-coat the blend solution on the substrate in step (2) at a spin-coating speed of 2000 rpm to form a film, and a thick active layer of about 120 nm is coated on the substrate surface; the structural formula of the compound BTR-Cl is shown in Formula 2 below; the structural formula of the acceptor L8-BO is shown in Formula 3 below. Formula 2 Formula 3

[0058] (4) Spin-coat the electron transport layer: Place the substrate obtained in step (3) in a 60 nm petri dish, then evenly apply 60 μL of chlorobenzene on its surface, perform solvent vapor annealing (85 °C, 5 min), and then spin-coat the electron transport layer PNDIT-F3N film on the above active layer at a spin-coating speed of 3000 rpm, with a film thickness of 10-20 nm; the structural formula of PNDIT-F3N is shown in Formula 4 below. Formula 4

[0059] (5) Evaporation of the top electrode: Deposit a 100-nm-thick metal electrode (commonly Ag, Al, etc.) on top of the electron transport layer by evaporation.

[0060] The specific organic solar cell efficiency is shown in Table 1 (the equipment used in the laboratory of the present invention is a solar simulator, calibrated with a silicon solar cell, and all tests are measured under 1 simulated sunlight, 100 mW / cm2).

[0061] Table 1 Photovoltaic conversion efficiency of all-small molecule photovoltaic devices

[0062] Active layer <![CDATA V oc (V)]]> <![CDATA J sc (mA / cm 2 )]]> FF (%) PCE (%) Compound Z-2F:L8-Bo 0.88 25.81 77.91 17.9 BTR-Cl:L8-Bo 0.86 24.52 76.31 16.1

[0063] From the data in Table 1, it can be seen that compared with the donor small molecule BTR-Cl containing a symmetric bridge, the PCE (power conversion efficiency) of the asymmetric donor material Z-2F with different fluorine atom contents has a significant improvement, and the compound Z-2F has increased from 16.1% to 17.9% compared with the small molecule BTR-Cl. The fill factor (FF) has increased from 76.31% to 77.91%, and the current density (J sc ) has increased from 24.52 mA / cm 2 to 25.81 mA / cm 2 . The proposed class of donor materials has a clear molecular structure in all-small molecule organic solar cells, with very small differences between the donor material, acceptor material, and device batches, so it has unique advantages in commercialization. It is of great significance for us to construct an efficient organic solar cell system.

[0064] Figure 7 This is the normalized UV-visible absorption spectrum of the compound Z-2F solution, Z-2F film, and L8-BO film prepared in the present invention. The results show that the compound Z-2F exhibits strong absorption in the range of 470 - 620 nm, which is complementary to the spectrum of L8-BO, facilitating the acquisition of a higher short-circuit current (J sc ). There is a red shift of about 50 nm for the strongest absorption peak from the solution state to the film state, indicating stronger π-π stacking during the film formation process. In the film, Z-2F has a strong shoulder peak, indicating good stacking of molecules in the pure film state and strong intermolecular interactions, which is beneficial for the formation of a good morphology of the blend film.

[0065] Figure 8Cyclic voltammograms of compounds Z-2F and L8-BO prepared according to the present invention (scan rate: 0.05 v per second). From the figure, the HOMO energy level of compound Z-2F can be calculated to be -11.35 eV, and its LUMO energy level is -2.85 eV, which matches well with the energy level of L8-BO. This is conducive to exciton dissociation and is expected to generate a higher open-circuit voltage, improving the photoelectric conversion efficiency of photovoltaic devices.

[0066] The solar cell includes a water-surface floating organic solar cell; the water-surface floating organic solar cell includes a battery panel made of Z-2F and a water-surface floating structure that can make the battery panel float on the water surface.

[0067] Example 3: Water-surface floating application of organic solar cells

[0068] In Example 2, a solar cell with a conventional structure such as ITO / PEDOT:PSS / active layer / PNDIT-F3N / Ag was prepared, and its photovoltaic performance was tested. A water-surface floating system was added to the bottom of the battery panel to increase the water-surface photovoltaic application. The water-surface floating system can be selected to be composed of a floating structure 1, a PV panel 2, a fixed bracket 3, and a hinge structure 4, which can make the battery panel float on the water surface and can adjust the tilt angle of the battery panel. The floating structure 1 can be selected from common floating structures such as floats; when the solar cell is placed on the water surface at two tilt angles of 0° and 30°, they can act as a thermal barrier to block sunlight and heat flux, significantly reducing the surface temperature of the water and slowing down the evaporation of the water; compared with the ground-mounted photovoltaic module, the operating temperature is reduced, increasing the lifespan of the solar photovoltaic module. The structural form of the water-surface floating system is as Figure 9 shown: The figure shows a tilt angle of 30°.

[0069] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, in any regard, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be encompassed within the present invention. Any reference signs in the claims should not be regarded as limiting the claims involved.

Claims

1. An asymmetric donor material with different fluorine contents, characterized in that, Its structural formula is shown in Formula 1: Formula 1.

2. The preparation method of the asymmetric donor material with different fluorine contents according to claim 1, characterized in that, It includes the following steps: S1: Using tetrahydrofuran as the solvent and iodine as the initiator, add magnesium powder and 4-bromo-1,2-difluorobenzene. Reflux the mixture at 70 °C for 4 h until the magnesium is completely consumed, and then naturally cool it to room temperature to obtain Grignard reagent 1. Drop Grignard reagent 1 into the toluene solution of benzo[1,2-b:4,5-b']dithiophene-4,8-dione, and stir at room temperature. Meanwhile, using tetrahydrofuran as the solvent and iodine as the initiator, add magnesium powder, , reflux the mixture at 70 °C for 2 h until the magnesium is completely consumed, and then naturally cool it to room temperature to obtain Grignard reagent 2. Then transfer the newly prepared Grignard reagent 2 to a dropping funnel and slowly drop it into the above mixed solution containing Grignard reagent 1. Subsequently, stir the mixture overnight at room temperature. Then, add stannous chloride (II) dihydrate dissolved in 10% (mass concentration) HCl at room temperature. Then continue to stir the resulting solution at 50 °C for 3 h; after completion, naturally cool it to room temperature and pour the reactant into water to obtain compound 1; S2: Under -78 °C and argon protection, a n-butyllithium solution was added dropwise to a tetrahydrofuran solution containing Compound 1. After addition, the mixture was stirred at -78 °C for 1 h, then a tetrahydrofuran solution of trimethyltin chloride was added. The mixture was continuously stirred at -78 °C for 1 h, and then naturally warmed to room temperature. After stirring at room temperature for 12 h, the solution was poured into deionized water, extracted three times with anhydrous diethyl ether, and dried with anhydrous sodium sulfate. After removing the solvent with a rotary evaporator, the crude product was recrystallized twice in toluene to obtain Compound 2; S3: Under argon protection, using tetrakis(triphenylphosphine)palladium as a catalyst and toluene as a solvent, Compound 2 and 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde were refluxed at 110 °C for 8 to 10 h to undergo a Stille coupling reaction to obtain Compound 3; S4: Under argon protection, Compound 3, 3-hexylrhodanine, and a base were added to the solvent chloroform, and a Knoevenagel condensation reaction was carried out at 60 °C to connect the rhodanine capping group to obtain an organic small molecule donor material with an asymmetric two-dimensional side chain.

3. The preparation method of the asymmetric donor material with different fluorine contents according to claim 2, characterized in that, In the above S1 , the molar ratio of 4-bromo-1,2-difluorobenzene, benzo[1,2-b:4,5-b']dithiophene-4,8-dione, and the tin reagent is 1:2:2.3, and the molar ratio of benzo[1,2-b:4,5-b']dithiophene-4,8-dione to the tin reagent is 1:

5.

4. The preparation method of the asymmetric donor material with different fluorine contents according to claim 2, characterized in that, The reflux reaction condition in S3 is reflux reaction at 110 °C for 9 h; the molar ratio of Compound 2 to 5''-bromo-3',3''-dihexyl-[2,2':5',2''-terthiophene]-5-carbaldehyde in S3 is 1:15, and the dosage ratio of the catalyst to Compound 2 is 20 mg:10.31 mmol.

5. The preparation method of the asymmetric donor material with different fluorine contents according to claim 2, characterized in that, The reaction time of the condensation reaction in S4 is 24 h; the molar ratio of 3-hexylrhodanine to Compound 3 in S4 is 15:

1.

6. Use of the asymmetric donor material with different fluorine contents according to any one of claims 1-5 in the preparation of the following functional energy devices: in the fields of solar cells, organic light-emitting diodes, and flexible displays.

7. Use of the asymmetric donor material with different fluorine contents according to claim 6, characterized in that, The solar cell includes a water-surface floating organic solar cell; the water-surface floating organic solar cell includes a battery panel made of the donor material and a water-surface floating structure.

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