A composite photo-anode of a flexible dye-sensitized solar cell based on a polyimide electrospun film and a preparation method thereof

Abstract

The application discloses a kind of based on polyimide electrospinning film's flexible dye-sensitized solar cell composite photoanode and preparation method thereof, it is related to solar cell technical field.The composite photoanode is obtained by pressure compounding by dye-sensitized composite semiconductor layer and flexible transparent conductive polymer film.The semiconductor layer of the composite photoanode of the present application is more closely connected, semiconductor layer can realize self-supporting, processing is simpler, production raw material cost is lower, with the advantages that solar light can be realized from the direction of photoanode incidence, with higher photoelectric conversion efficiency upper limit, semiconductor layer flexible big;On this basis, it solves the problem that polymer is difficult to be applied in high temperature manufacturing dye-sensitized solar cell photoanode field, and proposes a new idea for manufacturing flexible semiconductor layer.

Description

Technical Field

[0001] This invention relates to the field of electrode materials and electrode manufacturing technology for solar cells, and in particular to a composite photoanode for a flexible dye-sensitized solar cell based on a polyimide electrospun film and its preparation method. Background Technology

[0002] In 1839, French physicist Alexandre Edmond Becquerel discovered the photoelectric effect in his laboratory. This effect became the basis for the design of solar cells, and 30 years later, W.G. Adams and REDAY created the world's first solar cell. Due to the high cost and inconvenience of producing inorganic solar cells, in 1991, Brain, O'Regan, and Michael... For the first time, the doctor formed a nanoporous TiO2 semiconductor photoanode on conductive glass, using ruthenium-based dyes as photosensitizers and iodine-based I... - / I3 - Using a redox couple as the electrolyte and platinum, a metal with catalytic properties, as the counter electrode, the world's first dye-sensitized solar cell (DSSC) was fabricated, achieving a photoelectric conversion efficiency of 7.1%. (O'Regan B, MA low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films[J].Nature, 1991,353:737-740.) Although the photoelectric conversion efficiency of dye-sensitized solar cells is not as high as that of traditional crystalline silicon solar cells, they also have many unique advantages. The production process of dye-sensitized solar cells is simple, and their production cost is only about 20% of that of traditional crystalline silicon solar cells. (Li Jian, Wang Dingcheng, Bi Fei. Research progress on nanomaterials for dye-sensitized TiO2 solar cells[J]. Farmer's Advisor, 2019(12):199.)

[0003] However, rigid dye-sensitized solar cells still have limitations in application. They are not only heavy and impact-sensitive, but also lack flexibility, making them unsuitable for the miniaturization and wearable requirements of current electronic devices. Achieving TiO2 particle bonding and removing organic impurities from the TiO2 photoanode requires high-temperature sintering at temperatures exceeding 400°C. This excessively high sintering temperature is a major obstacle to the development of flexible dye-sensitized solar cells, as most flexible transparent materials cannot withstand such high temperatures. Therefore, researchers have been continuously exploring methods for low-temperature processing of the TiO2 photoanode, such as mechanical pressing, hydrothermal methods, electrochemical deposition, ultraviolet irradiation, and chemical sintering. These methods can improve the bonding tightness between TiO2 particles and the adhesion between the TiO2 film and the substrate at lower temperatures. For the first time, researchers pressure-treated an ITO / PET film coated with a TiO2 layer at room temperature, effectively obtaining a flexible TiO2 photoanode. Based on this, they fabricated a flexible dye-sensitized solar cell with a photoelectric conversion efficiency of 3%. H, Holmberg A, Magnusson E, et al. A new method to make dye-sensitized nanocrystalline solar cells at room temperature [C], Lausanne, 2001. Elsevier Science, 2001.) Zhang et al. used a hydrothermal method to transform the crystal form of TiO2 into rutile or anatase at the solid / gas interface, and then used a chemical reaction to connect the TiO2 particles. The photoelectric conversion efficiencies of rigid and flexible dye-sensitized solar cells obtained by the above method can reach 4.2% and 2.5%, respectively. (Zhang D, Yoshida T, Furuta K, et al. Hydrothermal preparation of porous nano-crystalline TiO2 electrodes for flexible solar cells[J]. Journal of Photochemistry and Photobiology A: Chemistry, 2004, 164(1-3): 159-166.) However, the semiconductor layer of dye-sensitized solar cells prepared by low-temperature methods has poor connectivity; its energy levels and band gaps are not as well matched with other components as those of semiconductor layers prepared by high-temperature methods; and the semiconductor cannot be self-supporting.

[0004] TiO2 layers can also be effectively formed on inorganic materials such as metals or their oxides as substrates. Meng et al. deposited a titanium film on a metal substrate using DC magnetron sputtering. In their further study, they found that when the sintering temperature of the substrate is higher than 500℃, the titanium film can form a dense bulk granular structure, and the photoelectric conversion efficiency of the dye-sensitized solar cell prepared by the photoanode formed at 700℃ can reach 2.26%. (Meng LJ, Wu MX, Wang YM, et al. Effect of the compact Ti layer on the efficiency of dye-sensitized solar cells assembled using stainless steel sheets[J]. Applied Surface Science, 2013, 275: 222-226.) Although semiconductor layers can be fabricated using high-temperature methods with metal materials as substrates, the opaque nature of flexible metal sheets prevents photoanodic intrusion, which limits the upper limit of their photoelectric conversion efficiency. Metal materials also face problems such as metal fatigue after repeated bending, resulting in poor flexibility. Metals and their oxides are unstable under acidic conditions, and some metals are easily corroded by electrolytes, leading to relatively poor stability of flexible dye-sensitized solar cells based on metal materials.

[0005] In summary, the fabrication methods for photoanodes that utilize organic polymers require low-temperature preparation, while high-temperature preparation necessitates the use of opaque metals or inflexible inorganic materials as substrates. Therefore, effectively resolving the conflicting requirements of flexible, transparent photoanodes and high-temperature fabrication presents a significant technical challenge limiting the development of dye-sensitized solar cells. Summary of the Invention

[0006] The purpose of this invention is to provide a composite photoanode for a flexible dye-sensitized solar cell based on a polyimide electrospun film and its preparation method, so as to solve the problems existing in the prior art.

[0007] To achieve the above objectives, the present invention provides the following solution:

[0008] This invention provides a composite photoanode for a flexible dye-sensitized solar cell, which is obtained by pressure bonding of a dye-sensitized composite semiconductor layer and a flexible transparent conductive polymer film. The transparent conductive polymer film can be divided into two parts: a conductive layer and a substrate, which can be arbitrarily combined. The conductive layer can be ITO, FTO, gold nanowire coating, silver nanowire coating, copper nanowire coating, or PEDOT:PSS coating. The substrate can be a flexible transparent polymer material such as PET, PEN, or polyimide.

[0009] The composite semiconductor layer includes a polyimide electrospun film substrate and a semiconductor layer, wherein the polyimide electrospun film substrate is distributed inside the semiconductor layer;

[0010] The pressure of the pressure composite is 20-150 MPa;

[0011] The semiconductor layer is made of one or more of titanium dioxide, zinc oxide, or tin dioxide.

[0012] The thickness of the composite semiconductor layer is 3-50 μm.

[0013] The pressure bonding process requires a high-hardness material to support the composite semiconductor layer, and a flexible material that does not chemically react with or adhere to the composite semiconductor layer is needed for protection. The support material is one of zirconium oxide, alumina, or diamond, and the protective material is one of PET, PEN, PEEK, PMMA, or polyimide film.

[0014] Furthermore, the polyimide electrospun film substrate is prepared from polyamic acid by electrospinning and thermal imidization treatment;

[0015] The polymerization monomers of the polyamic acid include diamine monomers and dianhydride monomers;

[0016] The diamine monomer is one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PPDA), or 2,2-bis(4-aminophenyl)hexafluoropropane (BAPAF); the dianhydride monomer is one or more of 1,2,4,5-pyromellitic dianhydride (PMDA), 4,4'-biphenyl ether dianhydride (ODPA), or 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA).

[0017] The molar ratio of the diamine monomer to the dianhydride monomer is 1:1. The monomers are added in the following order during polymerization: first the diamine monomer, then the dianhydride monomer, and the dianhydride monomer should be added in multiple portions of 1-5 parts. The polymerization temperature is -20 to 25°C, and the polymerization time is 6-48 hours. Polymerization is carried out under stirring conditions at a stirring speed of 15-240 r / min.

[0018] Preferably, the polyimide can be one or more of the following: polyacrylonitrile (PAN), polyetheretherketone (PEEK), polybenzimidazole, and blends or copolymers of the above three with poly(p-phenylene terephthalamide) that can meet the semiconductor layer processing temperature and light transmittance requirements; or copolymers or blends of polyamic acids with different molecular structures.

[0019] The present invention also provides a method for preparing the composite photoanode of the above-mentioned flexible dye-sensitized solar cell, comprising the following steps:

[0020] Step 1: Electrospinning a polyamic acid solution to obtain a polyamic acid electrospun film, followed by thermal imidization treatment to obtain the polyimide electrospun film substrate;

[0021] Step 2: Disperse the semiconductor slurry on the surface and inside the polyimide electrospun film substrate, and then dry it;

[0022] Step 3: The composite film dried in Step 2 is subjected to sintering and annealing. The sintering temperature is 450-500℃, and the annealing process is natural cooling, thereby obtaining the composite semiconductor layer.

[0023] Step 4: Adsorb dye onto the composite semiconductor layer and perform sensitization treatment to obtain a dye-sensitized composite semiconductor layer;

[0024] Step 5: The dye-sensitized composite semiconductor layer is pressure-composite with a flexible transparent conductive polymer film to obtain the composite photoanode of the flexible dye-sensitized solar cell.

[0025] The composite semiconductor layer prepared by this invention has a large specific surface area and energy levels and band gaps that match those of the dye; its semiconductor layer uses a polyimide electrospun film as a support layer.

[0026] In step 1, the solid content of the polyamic acid solution is 5-25 wt%.

[0027] In step 1, the organic solvent of the polyamic acid solution is one or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), or ethanol.

[0028] Step 1 also includes a step of degassing the polyamic acid solution, and the degassing method is one or more of the following: heating degassing, vacuum degassing, centrifugal degassing, and ultrasonic degassing.

[0029] In step 1, the liquid extrusion speed of electrospinning is 0.1-3 mL / h, the distance between the spinning head and the receiving roller is 10-30 cm, the spinning voltage is 10-25 kV, the rotation speed of the receiving roller is 100-500 r / min, and the spinning time is 1-60 min.

[0030] In step 1, the temperature of the thermal imidization treatment is 280-450℃, and the holding time is 30-60 min.

[0031] In step 2, the solvent in the semiconductor paste is one or more of ethanol, water, terpineol, and isopropanol.

[0032] In step 2, the dispersion thickness of the semiconductor paste is 10-250 μm.

[0033] In step 2, the drying temperature is 60-100℃ and the drying time is 1-24h.

[0034] In step 2, before dispersing the semiconductor slurry, the polyimide electrospun film substrate is cleaned: an ultrasonic cleaning method is used, and the cleaning agent is one or more of ethanol, water, isopropanol or acetone, and the cleaning time is 10-60 minutes.

[0035] In step 3, the sintering temperature is 450-500℃, the heating rate is 1-10℃ / min, and the holding time is 30-60min.

[0036] In step 4, the sensitization treatment is carried out at a temperature of 25-80℃ for 3-48 hours, and the concentration of the sensitizer used is 1×10⁻⁶. -4 -1×10 -3 mol / L; the sensitizer is one or more combinations of N719, N3, N712, Z907, N749, D102, D149, Z907Na, Z910, C101, D205 or C217.

[0037] The present invention also provides a flexible dye-sensitized solar cell, comprising the above-mentioned composite photoanode, a polymer thin film capable of accommodating an electrolyte space, an electrolyte, and a counter electrode.

[0038] The counter electrode is an ion sputtering counter electrode, which is prepared by ion sputtering metallic platinum onto the surface of a transparent conductive polymer film (cleaned by ultrasonic cleaning, the cleaning agent being one or more of ethanol, water, isopropanol, and acetone, and the cleaning time being 10-60 min).

[0039] The purity of the platinum metal target used in the ion sputtering should be 99.99% or higher, the ion sputtering time should be 30-600s, the ion sputtering environment pressure should be a vacuum environment of 0.01-10Pa, and the ion sputtering current should be 10-60mA.

[0040] This invention further provides a method for preparing the above-mentioned flexible dye-sensitized solar cell, comprising the following steps:

[0041] The composite photoanode and counter electrode are connected by heating using the polymer film that can accommodate the electrolyte space. Then, electrolyte is injected into the polymer film that can accommodate the electrolyte space, and the film is sealed to obtain the flexible dye-sensitized solar cell.

[0042] The polymer film that can accommodate the electrolyte space is one of PET, PP, PE, TPU or sarin film, with a thickness of 50-300μm and a heating connection temperature of 60-110℃.

[0043] The electrolyte is a mixed solution of acetonitrile containing 0.1-1 mol / L lithium iodide, 0.01-0.1 mol / L iodine, and 0.1-1 mol / L tetra-tert-butylpyridine; the sealing is performed by heat sealing with one of PET, PP, PE, TPU, or sarin film heated to 60-110°C.

[0044] When the composite semiconductor layer is pressure-bonded, a high-hardness pressure-resistant material is used as a support, and a flexible material is required to protect the composite semiconductor layer: the high-hardness pressure-resistant material has small deformation under high pressure, a compressive modulus of 1500MPa or above, a Mohs hardness of 8 or above, a surface roughness Ra<0.2μm, and a certain shear resistance; the flexible material has a surface roughness Ra<1.0μm, does not chemically react or adhere to the composite semiconductor layer, has a compressive modulus of 200MPa or above, is highly flexible, and has a certain shear resistance.

[0045] The prepared polyimide electrospun film substrate has a decomposition temperature of 450℃ or higher, a film thickness of 1-50μm, and a suitable amount of pores capable of supporting semiconductors.

[0046] This invention uses polyimide electrospun film as the substrate material for composite semiconductors, which not only has good high temperature resistance but also has a certain light transmittance, providing an effective means to solve the contradiction between flexible light transmittance of photoanodes and high temperature preparation.

[0047] Compared with traditional inorganic monocrystalline or polycrystalline silicon solar cells, dye-sensitized solar cells have advantages such as low production cost, easy process implementation, and wide application range. However, to further improve rigid dye-sensitized solar cells with glass substrates into flexible dye-sensitized solar cells, it is necessary to overcome the problem that flexible substrates cannot withstand the sintering temperature of the TiO2 semiconductor layer. Common flexible transparent polymers such as polyethylene, polypropylene, polyester, and plexiglass have melting points below 300°C, which is insufficient to meet the high temperatures required for TiO2 layer sintering. Polyimide, on the other hand, has a glass transition temperature above 300°C and a decomposition temperature reaching 500°C, enabling it to withstand the high temperatures required for TiO2 layer processing. Furthermore, fibers and films made from polyimide materials exhibit good flexibility and light transmittance. Therefore, this invention uses polyimide as a raw material, effectively solving the problem that flexible organic polymers cannot withstand the processing temperature of the TiO2 semiconductor layer, thus preparing a high-efficiency flexible dye-sensitized solar cell.

[0048] The present invention discloses the following technical effects:

[0049] This invention relates to a composite photoanode for flexible dye-sensitized solar cells based on polyimide electrospun films. Compared with photoanodes of traditional low-temperature manufactured dye-sensitized solar cells, it has advantages such as tighter connections between semiconductor layers, self-supporting semiconductor layers, simpler processing, and lower raw material costs. Compared with photoanodes of dye-sensitized solar cells based on metal substrates, it has advantages such as allowing sunlight to be incident from the photoanode direction, having a higher upper limit of photoelectric conversion efficiency, and greater flexibility of the semiconductor layer. On this basis, it solves the problem that polymers are difficult to apply in the field of high-temperature manufacturing of photoanodes for dye-sensitized solar cells, and proposes a new approach to manufacturing flexible semiconductor layers. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This invention describes the working principle and basic structure of the dye-sensitized solar cell.

[0052] Figure 2 This invention provides a process for preparing a composite photoanode for a flexible dye-sensitized solar cell based on a polyimide electrospun film.

[0053] Figure 3 The following are physical images of the flexible dye-sensitized solar cell of the present invention: (a) is the flexible counter electrode; (b) is the flexible composite photoanode; and (c) is the assembled flexible dye-sensitized solar cell.

[0054] Figure 4 This is a scanning electron microscope image of the composite photoanode surface in Embodiment 1 of the present invention;

[0055] Figure 5 IV curves for different embodiments and comparative examples; (a) IV curves for Examples 1-3; (b) IV curves for Examples 4-6; (c) IV curves for Examples 7-9; (d) IV curve for Comparative Example 1. Detailed Implementation

[0056] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0057] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0058] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0059] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0060] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0061] All dye-sensitized solar cells in the embodiments of this invention have a power density of 100 mW / cm². 2 The test was conducted under simulated sunlight at 1.5 AM.

[0062] Example 1

[0063] A composite photoanode based on ODA-ODPA type polyimide and its flexible dye-sensitized solar cell are prepared by the following steps:

[0064] (1) Using ODA as the diamine monomer, ODPA as the dianhydride monomer, and DMF as the organic solvent, dianhydride and diamine monomer were weighed in a highly accurate 1:1 molar ratio. The diamine monomer was added to the organic solvent first, and after complete dissolution, the dianhydride monomer was added in three portions. The polymerization temperature was 5℃, the stirring speed was 60 r / min, and the polymerization time was 12 h. The solid content of the polyamic acid solution after the polymerization reaction was 18 wt%.

[0065] (2) The polyamic acid solution was subjected to vacuum degassing treatment. After the bubbles in the solution were completely removed, electrospinning was performed. When electrospinning the polyamic acid solution, the liquid extrusion speed was 1.2 ml / h, the distance between the spinning head and the receiving roller was 20 cm, the spinning voltage was 16 kV, the rotation speed of the receiving roller was 300 r / min, and the spinning time was 10 min to obtain a polyamic acid electrospun film.

[0066] (3) The obtained polyamic acid electrospun film was subjected to thermal imidization treatment at a temperature of 350°C for 30 minutes. After natural cooling, the polyimide electrospun film substrate was obtained and ultrasonically cleaned in the following order: water for 20 minutes, isopropanol for 20 minutes, and ethanol for 20 minutes.

[0067] (4) After cleaning, titanium dioxide slurry (the solvent of the slurry is terpineol) is scraped onto the polyimide electrospun film substrate to fill the pores of the polyimide electrospun film. The scraping thickness is 50μm. The composite film after scraping is dried at a temperature of 60℃ for 2 hours.

[0068] (5) The dried composite film is subjected to high-temperature sintering at 450℃, with a heating rate of 5℃ / min and a holding time of 30min. After natural cooling, a composite semiconductor layer is obtained. The composite semiconductor layer is then further sensitized at 80℃ for 12h using a sensitizer of 5×10⁻⁶. -3 A mol / L N719 ethanol solution was used to obtain a composite semiconducting layer that adsorbed N719 dye, and then the layer was cleaned.

[0069] (6) The ITO conductive polymer film was ultrasonically cleaned in the following order: water for 20 min, isopropanol for 20 min, and ethanol for 20 min. The cubic zirconia, polyimide film, composite photoanode with adsorbed dye, ITO conductive polymer film (conductive layer is ITO, substrate is polyimide), and cubic zirconia were placed in the order from top to bottom and pressure of 37.3 MPa was applied to form a pressure bond, thus obtaining a flexible composite photoanode.

[0070] (7) A platinum metal layer (target purity 99.99%) was ion sputtered onto the surface of the cleaned ITO conductive polymer film. The ion sputtering time was 120s, the ion sputtering current was 30mA, and the ion sputtering ambient pressure was 1Pa to obtain a flexible counter electrode for dye-sensitized solar cells.

[0071] (8) The flexible composite photoanode, the 200μm thick TPU film with square holes cut out, and the flexible counter electrode are placed together in order from top to bottom, heated to 80℃, and kept at the temperature for 10min to obtain a flexible dye-sensitized solar cell without electrolyte injection, and iodine-based electrolyte is prepared at the same time.

[0072] (9) Iodine-based electrolyte is injected into a flexible dye-sensitized solar cell without electrolyte injection, and the TPU material is heated to 80°C for heat sealing to obtain a flexible dye-sensitized solar cell.

[0073] The iodine-based electrolyte used was a mixed solution of 0.5 mol / L lithium iodide, 0.05 mol / L iodine, and 0.5 mol / L tetra-tert-butylpyridine in acetonitrile.

[0074] Example 2

[0075] The specific operating steps are the same as in Example 1, except that the bonding pressure between the composite semiconductor and the transparent conductive polymer film is 74.6 MPa.

[0076] Example 3

[0077] The specific operating steps are the same as in Example 1, except that the bonding pressure between the composite semiconductor and the transparent conductive polymer film is 112 MPa.

[0078] Example 4

[0079] The specific operating steps are the same as in Example 3, except that the spinning time of the polyamic acid electrospun film is 20 minutes.

[0080] Example 5

[0081] The specific operating steps are the same as in Example 3, except that the spinning time of the polyamic acid electrospun film is 15 minutes.

[0082] Example 6

[0083] The specific operating steps are the same as in Example 3, except that the spinning time of the polyamic acid electrospun film is 5 minutes.

[0084] Example 7

[0085] The specific operating steps are the same as in Example 6, the only difference being the preparation of the polyamic acid solution:

[0086] ODA was selected as the diamine monomer and 6FDA as the dianhydride monomer. DMF was used as the organic solvent for polyamic acid. The dianhydride and diamine monomers were weighed in a highly accurate 1:1 molar ratio. The target polyamic acid solid content should be 18 wt%. The diamine monomer was added to the solvent first, and after complete dissolution, the dianhydride monomer was added in three portions. The polymerization temperature was 5°C, the stirring speed was 60 r / min, and the polymerization time was 12 h to obtain an ODA-6FDA type polyamic acid solution. The 18 wt% ODA-6FDA type polyamic acid solution was blended with an ODA-ODPA type polyamic acid solution to obtain a polyamic acid solution with an ODA-ODPA:ODA-6FDA mass ratio of 9:1. This solution was used to prepare a polyimide electrospun film substrate.

[0087] Example 8

[0088] The specific operating steps are the same as in Example 7, except that the blending ratio of ODA-ODPA type polyamic acid solution to ODA-6FDA type polyamic acid solution is 2:1.

[0089] Example 9

[0090] The specific operating steps are the same as in Example 7, except that the blending ratio of ODA-ODPA type polyamic acid solution to ODA-6FDA type polyamic acid solution is 0:10, that is, pure ODA-6FDA type polyamic acid solution.

[0091] Comparative Example 1

[0092] The FTO conductive glass was cleaned according to step (3) in Example 1, and titanium dioxide slurry (solvent for slurry is terpineol) was coated on it with a coating thickness of 50 μm. It was then dried at a temperature of 60 °C for 2 h. The FTO glass coated with titanium dioxide slurry was subjected to high-temperature sintering and sensitization treatment according to step (5) in Example 1 to obtain a rigid photoanode. The rigid dye-sensitized solar cell (electrolyte is the same as in Example 1) was assembled according to steps (7)-(9) in Example 1.

[0093] Table 1. Efficiency of dye-sensitized solar cells prepared under different conditions

[0094]

[0095] Analysis of the photoelectric conversion efficiencies of the examples and comparative examples given in Table 1 shows that changing the bonding pressure between the composite semiconductor layer and the transparent conductive polymer film can significantly affect the efficiency of flexible dye-sensitized solar cells. Increasing the bonding pressure from 37.3 MPa to 112 MPa corresponds to a 70.25-fold increase in the efficiency of the flexible dye-sensitized solar cells. The bonding pressure is one of the most important influencing factors on the efficiency of the flexible dye-sensitized solar cells described in this invention. The spinning time of the polyimide electrospun film substrate also has a significant impact; decreasing the spinning time from 20 min to 5 min increases the efficiency by 2.5 times. The trifluoromethyl groups in the ODA-6FDA type polyimide electrospun film have a high electronegativity, which can improve the light transmittance and electrochemical performance of the polyimide electrospun film. Based on a 2:1 blend ratio of polyimide electrospun film, the efficiency of the flexible dye-sensitized solar cell is 26.58% higher than that of the pure ODA-ODPA type polyimide electrospun film, and its efficiency can reach 65.57% of that of a rigid dye-sensitized solar cell prepared under the same conditions.

[0096] The efficiency of flexible dye-sensitized solar cells based on polyimide electrospun films with a blend ratio of ODA-ODPA and ODA-6FDA of 2:1 is a preferred embodiment in the examples.

[0097] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A composite photoanode for a flexible dye-sensitized solar cell, characterized in that, It is obtained by pressure bonding of a dye-sensitized composite semiconductor layer and a flexible transparent conductive polymer film; The composite semiconductor layer includes a polyimide electrospun film substrate and a semiconductor layer, wherein the polyimide electrospun film substrate is distributed inside the semiconductor layer; The pressure of the pressure composite is 20-150 MPa; The semiconductor layer is made of one or more of titanium dioxide, zinc oxide, or tin dioxide; The thickness of the composite semiconductor layer is 3-50 μm; The polyimide electrospun film substrate is prepared from polyamic acid by electrospinning and thermal imidization treatment; The polymerization monomers of the polyamic acid include diamine monomers and dianhydride monomers; The diamine monomer is one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, or 2,2-bis(4-aminophenyl)hexafluoropropane; the dianhydride monomer is one or more of 1,2,4,5-pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride, or 4,4'-(hexafluoroisopropene)diphthalic anhydride. The molar ratio of the diamine monomer to the dianhydride monomer is 1:1, the polymerization reaction temperature of the polymerizing monomer is -20 to 25°C, and the polymerization time is 6 to 48 hours. The liquid extrusion speed of the electrospinning is 0.1-3 mL / h, the distance between the spinning head and the receiving roller is 10-30 cm, the spinning voltage is 10-25 kV, the rotation speed of the receiving roller is 100-500 r / min, and the spinning time is 1-60 min. The temperature for the thermal imidization treatment is 280-450℃, and the holding time is 30-60 min; The composite semiconductor layer is obtained by dispersing semiconductor slurry on the surface and inside of a polyimide electrospun film substrate, drying it, and then sintering and annealing it. The sintering temperature is 450-500℃, the heating rate is 1-10℃ / min, and the holding time is 30-60min; The sensitization treatment temperature of the dye-sensitized composite semiconductor layer is 25-80℃, and the time is 3-48h; the concentration of the sensitizing agent used is 1×10⁻⁶. -4 -1×10 -3 mol / L; the sensitizing agent is one or more combinations of N719, N3, N712, Z907, N749, D102, D149, Z907Na, Z910, C101, D205 or C217.

2. The method for preparing the composite photoanode of the flexible dye-sensitized solar cell as described in claim 1, characterized in that, Includes the following steps: Step 1: Electrospinning a polyamic acid solution to obtain a polyamic acid electrospun film, followed by thermal imidization treatment to obtain the polyimide electrospun film substrate; Step 2: Disperse the semiconductor slurry on the surface and inside the polyimide electrospun film substrate, and then dry it; Step 3: The composite film dried in Step 2 is sintered and annealed to obtain a composite semiconductor layer; Step 4: Adsorb dye onto the composite semiconductor layer and perform sensitization treatment to obtain a dye-sensitized composite semiconductor layer; Step 5: Perform pressure bonding treatment on the dye-sensitized composite semiconductor layer and the flexible transparent conductive polymer film to obtain the composite photoanode of the flexible dye-sensitized solar cell.

3. A flexible dye-sensitized solar cell, characterized in that, It includes the composite photoanode as described in claim 1, a polymer film capable of accommodating an electrolyte space, an electrolyte, and a counter electrode.

4. The method for preparing a flexible dye-sensitized solar cell as described in claim 3, characterized in that, Includes the following steps: The composite photoanode and the counter electrode are connected by heating using the polymer film that can accommodate the electrolyte space. Then, electrolyte is injected into the polymer film that can accommodate the electrolyte space, and the film is sealed to obtain the flexible dye-sensitized solar cell. The electrolyte is an iodine-based electrolyte, using acetonitrile as the solvent. The types of solutes and their concentrations in the acetonitrile solution are 0.1-1 mol / L lithium iodide, 0.01-0.1 mol / L iodine, and 0.1-1 mol / L tetra-tert-butylpyridine, respectively. The heating temperature is 60-110℃.

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