Preparation method of P-SnO2 thin film and application of P-SnO2 thin film in flexible perovskite solar module

Abstract

The invention discloses a preparation method of a P-SnO2 film and application of the P-SnO2 film in a flexible perovskite solar module, and the preparation method comprises the following steps: adding a PAA aqueous solution into a SnO2 nanocrystalline stock solution, and mixing and diluting to obtain P-SnO2 ink; the method comprises the following steps: printing P-SnO2 ink on a flexible conductive substrate through a slit coating process, and carrying out annealing treatment to form a P-SnO2 thin film. The PAA is added into the SnO2 ink and is used as a cross-linking agent, so that the dispersity of SnO2 nanocrystals is improved, the drying process of a wet film in the printing process is optimized, and the volatilization of a solvent is slowed down, thereby preventing irregular sedimentation and agglomeration of the nanocrystals in the natural drying process, and finally obtaining the SnO2 film with improved uniformity, density and energy level structure. According to the P-SnO2 thin film prepared based on the method, a 30cm * 30cm flexible perovskite solar module with the photoelectric conversion efficiency reaching 16.40% is realized.

Description

Technical Field

[0001] The present invention belongs to the field of chemistry and photovoltaic technology, and specifically relates to a P-SnO 2 Thin film preparation methods and their applications in flexible perovskite solar modules. Background Art

[0002] In recent years, the development of perovskite solar cells (PSCs) has been rapid and has great prospects for industrial application. Compared with rigid perovskite solar cells, flexible perovskite solar cells (FPSCs) have the advantages of being wearable, lightweight, flexible and bendable, and can be applied to a wider range of application scenarios. Although small-area FPSCs have made significant progress in efficiency, the photoelectric conversion efficiency (PCE) tends to drop significantly when the size is enlarged, which is much lower than the efficiency of large-area rigid perovskite solar modules PSMs. Compared with inverted (pin) structured PSCs that rely heavily on high-energy vacuum processes, formal (nip) structured PSCs are more suitable for wet printing processes, which gives them great potential for cost reduction in large-scale production. In the nip structure, ETL, as the thinnest functional layer, has extremely high requirements for uniformity and density, which makes the scaled-up preparation of ETL extremely challenging. SnO 2 Nanocrystals are widely used as electron transport layers (ETLs) due to their high carrier mobility and low cost. Currently, related research focuses on the preparation of SnO by spin coating. 2 The lack of in-depth research on scalable technology is a major obstacle in the commercialization of flexible solar modules (FPSMs).

[0003] Bu et al. prepared SnO using the slot coating printing technique. 2 Electron transport layer, and successfully assembled a flexible mini-module with a size of 5cm×6cm, and its PCE reached 15.22%. However, in order to ensure that SnO 2 The uniformity of the film during the drying process requires the use of hot air to assist drying, which makes it more difficult to ensure the uniformity of the large-area SnO 2 To ensure the uniformity of the film, the uniformity of the air knife and the control accuracy of the air flow temperature must be considered. Li et al. used the wire rod coating method to prepare SnO 2 Nanocrystals and SnO 2 The double-layer ETL of nanorods is used to improve the density and bending resistance of nanocrystals, and based on this double-layer SnO 2 The 900 cm-2 nanostructured nanoparticle with a PCE of 16.40% was successfully prepared. 2 How to prepare uniform and dense SnO on a large area scale? 2Thin films have become a major challenge in printing large-area formal structures of FPSMs. Therefore, it is necessary to develop SnO films suitable for printing on large-area flexible conductive substrates. 2 Ink becomes the key. SnO 2 There is a clear difference between the ink and the perovskite ink. The perovskite ink is a true solution without any uniformity or precipitation issues, while the SnO 2 The ink is a slurry with a very low nanocrystal content, which is prone to nanocrystal agglomeration and sedimentation. 2 The monodispersity of nanocrystals in solvent and their subsequent film formation are decisive factors for the feasibility of large-scale printing. Summary of the invention

[0004] The present invention mainly studies the problem that the current preparation of FPSMs still uses a process that is not conducive to large-scale production. 2 The ink is difficult to match the printing requirements on flexible conductive substrates, resulting in SnO 2 The printing of the layer has become one of the main obstacles to expanding the production scale. To this end, the present invention proposes a P-SnO 2 Preparation method of thin film and its application in flexible perovskite solar panels, by adjusting SnO 2 The composition of the ink makes it suitable for slot die printing technology to prepare large-area, high-density SnO 2 thin films, ultimately improving the optoelectronic properties of large-area FPSMs.

[0005] The inventive concept of the present invention is to solve the problem of SnO 2 The dispersion problem of nanocrystals in ink and the subsequent film formation problem. The present invention proposes a method for regulating SnO 2 The method of ink is suitable for printing on flexible substrates to prepare SnO 2 The film has good uniformity and density. 2 The devices prepared by thin films show excellent photovoltaic performance. 2 A carboxyl-rich long-chain polymer polyacrylic acid (PAA) is added to the ink to react with SnO 2 The surface groups of the nanocrystals are cross-linked, which significantly improves the SnO 2 The dispersion of nanocrystals in the ink (the ink is labeled as P-SnO 2 ink). Using P-SnO 2 The ink can slow down the solvent evaporation rate and inhibit the agglomeration and sedimentation of nanocrystals during the printing process, making the prepared P-SnO 2 The film has improved uniformity, density and energy level structure. 2The prepared PSCs have improved PCE and anti-bending properties, and a 30 cm × 30 cm FPSM with a PCE of 16.40% was successfully fabricated.

[0006] In order to solve the above technical problems, the first aspect of the present invention provides a P-SnO 2 The method for preparing the film comprises the following steps:

[0007] (1) Add the PAA aqueous solution to SnO 2 The nanocrystal stock solution was mixed and diluted, and the supernatant was taken after centrifugation to obtain P-SnO 2 ink;

[0008] (2) The P-SnO 2 The ink is coated on a flexible conductive substrate and annealed to form the P-SnO 2 film.

[0009] In some embodiments of the present invention, the SnO 2 The volume ratio of the nanocrystal stock solution to the PAA aqueous solution is 1:(5-7).

[0010] In some embodiments of the present invention, the mixing and dilution is carried out by continuous stirring in an ice bath.

[0011] In some embodiments of the present invention, the preparation step of the PAA aqueous solution is: dissolving PAA in deionized water at 80-90° C. to prepare an aqueous solution of PAA with a concentration of 0.1-1.0 mg / mL. Using deionized water can avoid contamination of the product by mineral impurities.

[0012] In some embodiments of the present invention, the centrifugal speed is 8000-10000 rpm and the time is 5-10 min.

[0013] In some embodiments of the present invention, the coating method is a slit coating method. Compared with the traditional spin coating method, the slit coating method is more conducive to the uniformity and stability of the coating and is suitable for industrial continuous production.

[0014] In some embodiments of the present invention, the speed of the slot coating method is 0.5-1 m / min, and the feed rate is 0.2-0.3 mL / min.

[0015] In some embodiments of the present invention, the flexible conductive substrate is an indium-doped tin oxide (ITO) flexible conductive glass treated with ultraviolet ozone (UVO).

[0016] In some embodiments of the present invention, the UVO treatment time is 10-20 minutes.

[0017] In some embodiments of the present invention, the annealing treatment is performed at a temperature of 100-150°C.

[0018] In some embodiments of the present invention, the annealing treatment time is 0.5-1.5 hours.

[0019] A second aspect of the present invention provides a P-SnO 2 Thin film, the P-SnO 2 The film is prepared by the above preparation method, wherein the P-SnO 2 The area of ​​the film is not less than 800cm 2 The P-SnO prepared by the present invention 2 The film is uniform and dense, which is conducive to the preparation of efficient large-area flexible perovskite solar panels.

[0020] A third aspect of the present invention provides a flexible perovskite solar cell, wherein the flexible perovskite solar cell comprises an electron transport layer, wherein the electron transport layer is the above-mentioned P-SnO 2 film.

[0021] Compared with the prior art, the above technical solution of the present invention has at least the following technical effects or advantages:

[0022] (1) The present invention adds the aqueous solution of PAA to SnO 2 P-SnO was obtained by mixing and diluting the nanocrystal stock solution. 2 Ink, PAA as a crosslinker, and SnO 2 The surface groups of the nanocrystals are cross-linked, which slows down the volatilization of the solvent during the drying process of the wet film and prevents the irregular agglomeration of the nanocrystals during the natural drying process, thus obtaining a more uniform, denser P-SnO that is more compatible with the energy level of the perovskite. 2 Using it as the electron transport layer of flexible perovskite solar cells, large-area FPSMs with excellent photovoltaic performance can be prepared.

[0023] (2) P-SnO prepared by the present invention 2 The ink was printed on a flexible conductive substrate using a slot coating method. 2 The film does not require high-temperature annealing and is suitable for flexible substrates, which has great advantages in wearable electronic applications.

[0024] (3) P-SnO of the present invention 2 The film preparation method can be applied to the preparation and optimization of industrial electron transport layers. At the same time, the method of preparing flexible perovskite solar cells by slit coating method has the advantages of high repeatability, simple operation, low cost, etc., and achieves a photoelectric conversion efficiency of more than 16%, which has excellent industrial application value and prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 SnO with different concentrations of PAA 2 Ink optical pictures;

[0026] Figure 2 The SnO prepared in Example 1 and Comparative Example 1 of the present invention 2 Scanning electron microscope (SEM) morphology of the film;

[0027] Figure 3 The SnO prepared in Example 1 and Comparative Example 1 of the present invention 2 Schematic diagram of the wet film drying process of the thin film;

[0028] Figure 4 The SnO prepared in Example 1 and Comparative Example 1 of the present invention 2 Schematic diagram of the energy level structure of thin films and perovskite films;

[0029] Figure 5 JV curves of the flexible solar cells prepared in Example 1 of the present invention and Comparative Example 1;

[0030] Figure 6 This is a JV curve diagram of a large-area flexible solar cell prepared in Comparative Example 2 of the present invention;

[0031] Figure 7 This is a JV curve diagram of the large-area flexible solar cell prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the examples, so that the technical personnel of the relevant technical field can understand the present invention. It is necessary to point out here that the examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. The non-essential improvements and adjustments made to the present invention by the skilled person in the relevant field according to the above invention content should still belong to the scope of protection of the present invention. At the same time, the raw materials mentioned below that are not described in detail are all commercially available products; the process steps or preparation methods that are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0033] Example 1

[0034] A P-SnO 2 The method for preparing the film comprises the following steps:

[0035] (1) A 30 cm×30 cm ITO PEN flexible conductive substrate was etched by a femtosecond laser, and the substrate was placed in a container containing isopropyl alcohol (IPA) and ultrasonicated for 15 minutes to ensure that the surface of the flexible substrate was clean and free of stains; then, the surface of the substrate was blown dry with a nitrogen air gun and placed in an ultraviolet ozone cleaning machine for 15 minutes before use to obtain a UVO-treated ITO PEN flexible conductive substrate.

[0036] (2) Preparation of P-SnO 2 Ink: Weigh 10 mg of PAA and 10 mL of deionized water, mix them, and stir at 90 °C to completely dissolve them to obtain a PAA aqueous solution with a concentration of 1 mg / mL. 2 The nanocrystal stock solution and the PAA aqueous solution were mixed and diluted in a volume ratio of 1:6, and the mixture was continuously stirred in an ice bath during the mixing and dilution process. The diluted solution was then centrifuged at a speed of 10000 rpm for 5 minutes, and the supernatant was taken to prepare P-SnO 2 Ink, refrigerate until ready to use.

[0037] (3) Preparation of P-SnO by slit coating method 2 Thin films: Adding P-SnO in a slot coater 2 The ink was coated at a rate of 0.5 m / min, a feed rate of 0.25 mL / min, and a gap of 120 μm between the coating blade and the substrate. After coating, the flexible substrate was placed on a hot plate and heated at 150 °C for 1 hour to form a PAA-doped tin oxide film, denoted as P-SnO 2 film.

[0038] A method for preparing a flexible perovskite solar cell comprises the following steps:

[0039] 1) Preparation of perovskite layer: Prepare the prepared FAPbI 3 The perovskite precursor solution (1.53 mmol lead iodide, 1.4 mmol formamidine hydroiodide, 0.5 mmol methylamine hydrochloride, 0.8 mL N,N-dimethylformamide (DMF) and 0.1 mL dimethyl sulfoxide (DMSO)) was shaken for 1 hour and set aside. A 30 cm × 30 cm P-SnO 2 The film substrate was cut into 2cm×2cm square pieces and UVO treated for 15 minutes. The perovskite film was prepared by spin coating, and the entire spin coating process was carried out in a nitrogen glove box. The spin coating parameters were a rotation speed of 6000rpm and an acceleration of 2000rpm. The whole process lasted for 30 seconds. 100μL of ethyl acetate (EA) was added at 25 seconds after the start of spin coating, and the obtained film was annealed on a 100℃ hot stage for 1 hour.

[0040] 2) Preparation of 2D layer: 2 mg of butylamine iodide (iBAI) and 2.8 mg of potassium di(fluoromethanesulfonyl)imide (KFSI) were dissolved in 1 mL of isopropanol / tetrahydrofuran (THF) mixed solvent (volume ratio 95:5); after the substrate was cooled, 3 30 μL of iBAI / K-FSI solution was dynamically spin-coated on the perovskite film at 5000 rpm for 10 seconds and then annealed at 100 °C for 10 minutes.

[0041] 3) Preparation of hole transport layer: First, 0.091g of 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD) powder, 1mL of chlorobenzene, 35.6μL of 4-tert-butylpyridine, 21μL of acetonitrile solution of lithium bis(trifluoromethanesulfonyl)imide (520g / L) and 11μL of acetonitrile solution of FK209 cobalt salt (300g / L) were mixed to prepare Spiro-OMeTAD solution; the solution was spin-coated on the perovskite light absorption layer to obtain the Spiro-OMeTAD hole transport layer; the spin-coating parameters were a rotation speed of 3000rpm, and the whole process lasted for 30 seconds to obtain the Spiro-OMeTAD hole transport layer. The prepared film was placed in a drying cabinet with a relative humidity below 20% for 10-15 hours to ensure that the chlorobenzene was completely volatilized.

[0042] 4) Preparation of gold electrode layer: After the spin coating of Spiro-OMeTAD is completed, the functional layer film of the positive and negative electrodes is etched with a laser to expose the conductive electrode. A gold vaporization mask is attached to leave the gold vaporization area; gold with a thickness of 80-100nm is deposited on the Spiro-OMeTAD hole transport layer by vacuum evaporation to form a gold counter electrode, thereby producing a flexible perovskite solar cell.

[0043] Example 2

[0044] P-SnO of Example 2 2 The preparation method of the film is the same as that of Example 1.

[0045] Preparation of large-area (30cm×30cm) flexible perovskite solar panels: The slit coating method was used to coat 30cm×30cm P-SnO 2 The perovskite layer, 2D layer and hole transport layer are printed on the / ITO / PEN substrate in sequence, and the printing process is carried out in ambient air. The specific steps include:

[0046] First, the perovskite wet film was printed by printing the perovskite precursor solution on the P-SnO substrate at a feed rate of 1.8 mL / min and a speed of 0.6 m / min. 2On the film substrate. Dry the wet film by quickly evacuating to 5Pa and holding for 5-15 seconds. Then, transfer the preliminarily dried perovskite film to a hot stage and anneal at 100°C for 60 minutes. Secondly, print the 2D layer, print the 2D layer at a printing speed of 0.3m / min and a feed rate of 0.4mL / min, and then anneal at 100°C for 10 minutes. Finally, print the HTL layer, and print the hole transport layer at a coating speed of 0.5m / min and a feed rate of 1mL / min. Place the prepared film in a drying cabinet with a relative humidity of less than 20% for 10-15 hours to ensure that the chlorobenzene is completely volatilized. Gold with a thickness of 80-100nm is deposited on the Spiro-OMeTAD hole transport layer by vacuum evaporation to form a gold counter electrode to produce a large-area flexible perovskite solar cell module.

[0047] Modularization of large-area flexible perovskite solar cells: P1 line was etched with a femtosecond laser (FemtoYL, 1030nm). P2 and P3 lines were etched with a picosecond laser (GS-PGN30). P1 was etched before the ITO PEN flexible conductive substrate was cleaned. P2 was etched after HTL preparation. P3 was etched after the gold electrode was deposited.

[0048] Comparative Example 1

[0049] A C-SnO 2 The method for preparing the film comprises the following steps:

[0050] (1) A 30 cm×30 cm ITO PEN flexible conductive substrate was etched by a femtosecond laser, and the substrate was placed in a container containing isopropyl alcohol (IPA) and ultrasonicated for 15 minutes to ensure that the surface of the flexible substrate was clean and free of stains; then, the surface of the substrate was blown dry with a nitrogen air gun and placed in an ultraviolet ozone cleaning machine for 15 minutes before use to obtain a UVO-treated ITO PEN flexible conductive substrate.

[0051] (2) Configuration of C-SnO 2 Ink: SnO 2 Deionized water was added to dilute the nanocrystal stock solution (SnO 2 The volume ratio of the nanocrystal stock solution to deionized water was 1:6), and the mixture was stirred in an ice bath during the mixing process. The diluted solution was then centrifuged at a speed of 10,000 rpm for 5 minutes, and the supernatant was taken to prepare SnO 2 The diluted dispersion is denoted as C-SnO 2 ink.

[0052] (3) Preparation of C-SnO by slit coating method 2 Thin films: Adding C-SnO in a slot coater 2The ink was coated at a rate of 0.5 m / min, a feed rate of 0.25 mL / min, and a gap of 120 μm between the coating head and the substrate. After coating, the flexible substrate was placed on a hot plate and heated at 150 °C for 1 hour to form a tin oxide film, which was recorded as C-SnO 2 film.

[0053] The preparation method of the flexible perovskite solar cell of Comparative Example 1 is the same as that of Example 1.

[0054] Comparative Example 2

[0055] Comparative Example 2 C-SnO 2 The preparation method of the film is the same as that of Comparative Example 1.

[0056] The preparation method of large-area flexible perovskite solar cell in comparative example 2 is different from that in example 2 in that P-SnO 2 Thin film replacement with C-SnO 2 film.

[0057] Performance Testing

[0058] 1. Characteristics of tin oxide ink

[0059] Figure 1 a is C-SnO prepared in comparative example 1 without adding PAA 2 Pictures of ink under laser irradiation; Figure 1 b is the preparation method of Example 1, using different concentrations of PAA aqueous solution to prepare P-SnO 2 When the concentration of PAA is 0.5 mg / mL, P-SnO 2 The Tyndall effect of the ink is slightly enhanced, higher than that of C-SnO without adding PAA. 2 ink, indicating that SnO 2 The nanocrystals in the ink were cross-linked and sedimentation was reduced. When the PAA concentration reached 1 mg / mL, part of the ink began to form a gel-like precipitate. As the PAA concentration further increased to 2 mg / mL, it could even turn into an opaque viscous gel. This shows that PAA can change the SnO 2 Surface properties of nanocrystals.

[0060] 2. Microstructure of tin oxide film

[0061] Figure 2 a and Figure 2 b are C-SnO prepared in Comparative Example 1 and Example 1 respectively. 2 Thin Film and P-SnO 2 SEM surface micromorphology of the film, C-SnO 2The SEM images of the films show obvious large grain protrusions and holes, which are not conducive to the bonding of perovskite and SnO 2 Efficient charge transfer between electron transport layers. In contrast, P-SnO 2 The morphology is uniform and flat, which is conducive to the subsequent preparation of perovskite films and good charge transfer between interfaces.

[0062] 3. Analysis of the principle of tin oxide film formation process

[0063] Figure 3 It shows that during the printing process, different SnO 2 Schematic diagram of the drying process of wet film. Figure 3 SnO 2 nanocrystal and SnO 2 NCs represents SnO 2 Nanocrystals, Incomplete covered C-SnO 2 Film indicates C-SnO with incomplete coverage 2 Thin film, Well-covered P-SnO 2 Film means P-SnO with good coverage 2 film. Figure 3 a is C-SnO 2 During the film drying process, as the solvent evaporates, C-SnO 2 Nanocrystals gradually precipitate and agglomerate, eventually forming C-SnO with uneven distribution and poor density. 2 Film. Figure 3 b It can be seen that as the solvent evaporates, P-SnO 2 The nanocrystals in the wet film are evenly distributed and gradually shrink under the entanglement and cross-linking of PAA. As the concentration increases, the wet film changes from the initial fluid state to the viscous state, which slows down the drying speed of the wet film. During this drying process, the fluidity of the wet film decreases sharply, avoiding the formation of uneven drying areas due to irregular ink flow. At the same time, the P-SnO in the wet film 2 The gaps between nanocrystals gradually decrease under the stretching effect of PAA, eventually forming a uniform and dense P-SnO 2 membrane.

[0064] 4. Properties of tin oxide film

[0065] Figure 4 C-SnO prepared in Comparative Example 1 and Example 1 2 Thin Film and P-SnO 2 Schematic diagram of the energy level structure of the film and the perovskite film, where PVK refers to the perovskite film prepared by the slit coating method. Figure 4 It can be seen that P-SnO2 The conduction band of the film is closer to the conduction band of the perovskite film, and the more matched band structure helps to transport charge carriers more efficiently and reduce the non-radiative recombination of interface charges, thereby optimizing the photovoltaic performance of flexible perovskite solar cells.

[0066] 5. Photovoltaic performance of flexible perovskite solar cells

[0067] The flexible perovskite solar cells prepared in Examples 1 and 2 and Comparative Examples 1 and 2 were tested respectively, and the test light intensity was one sun (AM1.5G, 100 mW / cm 2 ), calibrated with standard silicon cells, with a test area of ​​0.1486cm 2 ,The results of reverse (RS) and forward (FS) scanning are shown in Table 1.

[0068] Table 1:

[0069]

[0070] Figure 5 The C-SnO with the best performance of the perovskite solar cell prepared in Example 1 of the present invention and Comparative Example 1 2 and P-SnO 2 Current density (Current Density)-voltage (Voltage) (JV) curve of FPSCs based on P-SnO 2 The base device achieved a photoelectric conversion efficiency (PCE) of 22.54%, and its corresponding open circuit voltage (V OC ) is 1.163V, and the short-circuit current density (J SC ) is 24.30mA / cm 2 , the filling factor (FF) is 0.797. C-SnO 2 The PCE of the device is 21.07%, and its corresponding open circuit voltage is 1.120 V and short circuit current is 23.93 mA / cm 2 , the filling factor is 0.786. That is, P-SnO 2 Base device V OC , J SC and FF are both higher.

[0071] Figure 6 For use with an opening area of ​​600cm 2 JV curve of the FPSM based on comparative example 2 of the present invention tested with a mask. 2 The PCE of the base FPSM is 11.65% (as shown in Table 1, Comparative Example 2, J SC =0.526mA / cm 2 , V OC=40.223V, FF=0.551). The FF of this component is low, which is due to the fact that C-SnO 2 The uneven distribution and poor coverage of the film lead to increased non-radiative recombination of interfacial charges, which ultimately degrades the performance of FPSM.

[0072] Figure 7 For use with an opening area of ​​600cm 2 JV curve of the FPSM based on Example 2 of the present invention tested by the mask. 2 The PCE of the FPSM-based product reached 16.4% (as shown in Table 1, Example 2, J SC =0.547mA / cm 2 , V OC =40.772V, FF=0.735), the introduction of PAA effectively improved the SnO 2 The film flatness and density, as well as the better match between the interface energy level of the PVK layer, indicate that this method is helpful for preparing efficient large-area FPSMs.

[0073] For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, without having to go through creative labor. Therefore, simple improvements made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the protection scope of the present invention. The above embodiments are preferred embodiments of the present invention, and all processes similar to the present invention and equivalent changes made should belong to the protection scope of the present invention.

Claims

1. A method for preparing a P-SnO2 thin film, characterized in that: The following steps are involved: (1) adding an aqueous solution of polyacrylic acid to a stock solution of SnO2 nanocrystals, mixing and diluting the mixture, and taking a supernatant after centrifugation to obtain a P-SnO2 ink; (2) The P-SnO2 ink is coated on a flexible conductive substrate and subjected to annealing treatment to form the P-SnO2 film.

2. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The volume ratio of the SnO2 nanocrystal stock solution to the polyacrylic acid aqueous solution is 1:(5-7).

3. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The mixing and dilution method is continuous stirring in an ice bath.

4. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The preparation step of the polyacrylic acid aqueous solution is as follows: dissolving polyacrylic acid in deionized water at 80-90° C. to obtain a polyacrylic acid aqueous solution with a concentration of 0.1-1.0 mg / mL.

5. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The centrifugal speed is 8000-10000 rpm and the time is 5-10 min.

6. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The coating method is a slot coating method.

7. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The flexible conductive substrate is an ITO flexible conductive PEN substrate treated with ultraviolet ozone.

8. The method for preparing a P-SnO2 thin film according to claim 1, characterized in that: The annealing treatment is performed at a temperature of 100-150° C. and / or the annealing treatment is performed for a time of 0.5-1.5 hours.

9. A P-SnO2 thin film, characterized in that: The P-SnO2 film is prepared by the preparation method according to any one of claims 1 to 8, and the area of ​​the P-SnO2 film is not less than 800 cm 2 .

10. A flexible perovskite solar cell, characterized in that: The flexible perovskite solar cell includes an electron transport layer, and the electron transport layer is the P-SnO2 thin film according to claim 9.

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