An inorganic perovskite thin film, its preparation method and application

Abstract

This invention belongs to the field of perovskite thin film and solar cell technology, specifically relating to an inorganic perovskite thin film, its preparation method, and its application. The thin film comprises CsPbI3 and polyacrylonitrile, with the polyacrylonitrile content ranging from 0.001 to 0.01 wt%. This invention uses dimethylammonium lead iodide and cesium iodide as precursors, combined with the regulating effect of polyacrylonitrile, to promote the orderly growth of perovskite crystals. The addition of polyacrylonitrile can assist in regulating the perovskite crystallization process and reduce residual stress during crystallization. Simultaneously, this invention employs a rapid annealing process to shorten the preparation time and obtains a high-quality perovskite thin film through optimized crystallization kinetics. This invention utilizes extremely low amounts of polyacrylonitrile as a multifunctional additive, effectively passivating ionic defects, avoiding the obstruction of charge transport by excessive polymer, and improving the photoelectric conversion efficiency of the battery. The preparation method is simple, low-cost, and conducive to large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of perovskite thin film and solar cell technology, specifically relating to an inorganic perovskite thin film, its preparation method and application. Background Technology

[0002] All-inorganic perovskite materials, represented by CsPbX3 (X = Cl, Br, I), have higher thermal and environmental stability compared to organic-inorganic hybrid perovskites. They also exhibit excellent photoelectric properties such as high absorption coefficient, suitable wide bandgap (Eg ≥ ​​1.7eV), and long carrier diffusion length, making them highly promising candidates for next-generation photovoltaic devices.

[0003] Among various all-inorganic perovskite materials, CsPbI3 has attracted widespread attention due to its good bandgap (approximately 1.73 eV) matching the solar spectrum and its high theoretical photoelectric conversion efficiency. Since Professor Henry J. Snaith of Oxford University first fabricated a CsPbI3 perovskite solar cell in 2015, this field has experienced rapid development, with continuous improvement in device efficiency. However, a series of technical challenges still exist in further improving the photoelectric conversion efficiency and stability of all-inorganic perovskite solar cells.

[0004] First, residual strain exists in the CsPbI3 perovskite thin film structure prepared by conventional solution spin coating, resulting in smaller perovskite grain size, increased grain boundaries, and consequently, an increased defect state density. Second, internal defects in the film (such as uncoordinated Pb) contribute to this. 2+ Halogen ions (such as halogen vacancies) become nonradiative recombination centers for photogenerated carriers, severely limiting carrier collection efficiency and reducing the open-circuit voltage and fill factor of the battery. Furthermore, the migration behavior of halide ions under an electric field easily introduces new defects into the perovskite layer, further deteriorating the long-term operational stability of the device. Studies have shown that strategies such as reducing and passivating defects in perovskite films and increasing the ion migration activation energy can effectively suppress ion migration in perovskite, thereby improving the operational stability of the device.

[0005] To address the aforementioned issues, researchers have attempted to introduce polymer additives to regulate perovskite thin films. Polymer additives can play multiple roles: on the one hand, they regulate the crystallization kinetics of perovskite, promoting grain growth and preferred orientation; on the other hand, they passivate defects and reduce non-radiative recombination by forming coordination bonds or hydrogen bonds between functional groups in the polymer and uncoordinated ions on the perovskite surface. For example, Chinese patent document CN116632083A discloses a "hydrogen-bonded assisted inorganic perovskite thin film," which introduces a polymer capable of forming hydrogen bonds with dimethylammonium iodide (DMAI). This hydrogen bonding lowers the escape energy barrier of DMA, accelerating the crystallization kinetics of CsPbI3, thereby obtaining a uniform, non-porous, and highly crystalline CsPbI3 thin film. This approach also suppresses iodine vacancies and improves phase stability through hydrogen bonds between polymer residues and CsPbI3. However, this technical solution mainly focuses on the phase stability of the film itself, requiring a high polymer addition amount and a long annealing time (10-30 minutes).

[0006] It is evident that current technologies still lack a comprehensive solution that can both regulate the perovskite crystallization process and effectively passivate thin film defects, thereby synergistically reducing defect state density and minimizing nonradiative recombination. In particular, how to significantly improve the electrical quality of the thin film while ensuring its phase stability, and how to systematically apply it to high-efficiency all-inorganic perovskite solar cells, is a pressing technical challenge that needs to be addressed in this field. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide an inorganic perovskite thin film, its preparation method, and its applications. It utilizes an extremely low amount of polyacrylonitrile to exert a multifunctional synergistic regulatory effect: on the one hand, it regulates the perovskite crystallization kinetics, promoting grain growth; on the other hand, it passivates film defects through functional groups, reducing defect state density and minimizing non-radiative recombination. Combined with a rapid annealing process, high-quality perovskite thin films are obtained while significantly shortening the preparation time, thereby improving the optoelectronic performance of devices.

[0008] The technical solution adopted is as follows: An inorganic perovskite thin film comprising CsPbI3 and polyacrylonitrile, wherein the polyacrylonitrile content in the film is 0.001–0.1 wt%. The polyacrylonitrile in the film is used to simultaneously achieve at least two of the following functions: regulating the crystallization process, passivating defects, reducing defect state density, and reducing non-radiative recombination.

[0009] This invention provides a method for preparing inorganic perovskite thin films, comprising the following steps: (a) Dissolving polyacrylonitrile in an organic solvent to form a polyacrylonitrile solution, wherein the concentration of the polyacrylonitrile solution is 0.1 to 1 mg / mL; (b) Dissolve dimethylammonium lead iodide and cesium iodide in a mixed solvent to form a CsPbI3 precursor solution; (c) Add the polyacrylonitrile solution from step (a) to the CsPbI3 precursor solution from step (b) and mix thoroughly to form a film precursor solution; wherein, the amount of polyacrylonitrile solution added is 0.01 to 0.1 mL relative to 1 mL of CsPbI3 precursor solution. (d) Spin-coat the film precursor solution from step (c) into a film, and then anneal it in air for 3 to 15 minutes to obtain an inorganic perovskite film.

[0010] Preferably, in step (a), the organic solvent is any one or a mixture of N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, and thiocyanate solution; polyacrylonitrile is added to DMF and stirred overnight on a heating table at 40-70°C.

[0011] Preferably, in step (b), the molar ratio of dimethylammonium lead iodide (DMA PbI3, i.e., dimethylammonium, lead iodide) and cesium iodide (CsI) is in the range of 1:0.9-1.1:0.9-1.1; the mixed solvent is a mixture of DMF and DMSO at a volume ratio of 9:1 to prepare a CsPbI3 perovskite precursor solution with a concentration of 0.6-1.0 mol / L.

[0012] Preferably, in step (c), after the mixture is homogeneous, it is heated and stirred overnight at a temperature of 50-60°C to form a thin film precursor solution.

[0013] Preferably, in step (d), before spin coating, the film precursor solution is filtered through a 0.22 μm nylon filter head and then spin coated at a spin coating speed of 2000–4000 rpm for 20–50 s. After spin coating, the film is annealed in air at a temperature of 180–210 °C for 3–15 min to obtain an inorganic perovskite film.

[0014] The overnight stay described in this invention is 10 to 12 hours.

[0015] The present invention also provides an application of an inorganic perovskite thin film in an all-inorganic perovskite solar cell, the cell comprising a transparent conductive substrate, an electron transport layer, the inorganic perovskite thin film of claim 1 as a photoactive layer, a hole transport layer, and a back electrode, which are stacked sequentially. The transparent conductive substrate is cleaned FTO conductive glass, the electron transport layer is a TiO2 layer, the hole transport layer is a Spiro-OMeTAD layer, and the back electrode is an Ag electrode.

[0016] Preferably, the electron transport layer is prepared by the following method: The FTO conductive glass is cleaned by plasma cleaning, with a plasma cleaning power of 40-100 W and a cleaning time of 3-15 min. After cleaning, the FTO conductive glass is immersed in TiCl4 aqueous solution and deposited in a water bath at 60-90℃ for 1 hour, and then annealed at 100-200℃ for 30-60 minutes.

[0017] Preferably, the hole transport layer is prepared by the following method: Spiro-OMeTAD is dissolved in chlorobenzene to prepare a spin-coating solution with a concentration of 72-90 mg / mL, and then Li-TFSI and 4-tert-butylpyridine are added. After stirring overnight, the solution is spin-coated to form a film. The mass ratio of Spiro-OMeTAD, Li-TFSI, and 4-tert-butylpyridine is 72–90:100–200:5–20; the spin coating speed is 2000–5000 rpm, and the spin coating time is 20–40 s.

[0018] Preferably, the back electrode is formed by vapor deposition, with a vapor deposition vacuum degree of 5×10⁻⁶. -4 Pa, evaporation rate of 0.3 Å / s, thickness of 80–100 nm.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention utilizes a very low amount of polyacrylonitrile (the residual amount in the film is only 0.001-0.1 wt%) as a multifunctional additive, which can effectively passivate ionic defects in the film, avoid the obstruction of charge transport by excessive polymer, achieve a balance between "passivating defects" and "maintaining conductivity", significantly reduce the defect state density of the film, reduce non-radiative recombination at grain boundaries, and can help reduce the energy loss of perovskite solar cells.

[0020] (2) This invention uses dimethylammonium lead iodide (DMAPbI3) and cesium iodide (CsI) as precursors, combined with the regulating effect of polyacrylonitrile, to promote the orderly growth of perovskite crystals. The addition of polyacrylonitrile can help regulate the perovskite crystallization process, reduce the residual stress of perovskite crystallization, and help form a uniform, continuous, and pinhole-free film, thereby enhancing the coverage and crystallinity of the perovskite layer. At the same time, this invention uses a rapid annealing process (3-15 minutes), which significantly shortens the preparation time, and obtains high-quality perovskite films by optimizing crystallization kinetics.

[0021] (3) Through the synergistic effect of defect passivation and crystallization regulation, the all-inorganic CsPbI3 perovskite solar cell prepared in this invention shows significant improvements in open-circuit voltage, fill factor, and photoelectric conversion efficiency. The introduction of polyacrylonitrile prolongs carrier lifetime, promotes energy level alignment between the perovskite layer and the hole transport layer, and improves interfacial carrier transport and extraction efficiency. When the thin film prepared after polyacrylonitrile regulation is applied to solar cells, its photoelectric conversion efficiency increases from 17.50% to 21.06%.

[0022] (4) Polyacrylonitrile has good hydrophobic properties. When introduced into a perovskite film, it can slow down the erosion of the CsPbI3 black phase by humidity and improve the phase stability of the black phase CsPbI3. At the same time, the interaction between polyacrylonitrile residue and CsPbI3 can inhibit the formation of iodine vacancies, enhance the structural stability of the perovskite material, thereby enhancing the environmental stability of the device and extending the working life of the device.

[0023] (5) The preparation method of the present invention is simple to operate and does not require complex equipment or harsh environmental control. The preparation (0.1-1 mg / mL) and addition (0.01-0.1 mL / mL precursor solution) of the polyacrylonitrile solution are easy to achieve, and the annealing can be carried out in air without the need for strict control of the inert atmosphere, which reduces the preparation cost and the requirements for equipment, and is conducive to large-scale industrial production. Attached Figure Description

[0024] Figure 1 The images show a comparison of SEM images of the inorganic perovskite films prepared in Example 1 and Comparative Example 1.

[0025] Figure 2 The images show a comparison of XRD patterns of the inorganic perovskite thin films prepared in Example 1 and Comparative Example 1.

[0026] Figure 3 The PL comparison spectra of the inorganic perovskite thin films prepared in Example 1 and Comparative Example 1 are shown.

[0027] Figure 4 XPS comparison images of inorganic perovskite thin films prepared in Example 1 and Comparative Example 1.

[0028] Figure 5 This is a flowchart of the all-inorganic perovskite solar cell prepared in Example 1 of the present invention.

[0029] Figure 6 The image shows a comparison of the JV curves of the all-inorganic perovskite solar cells prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0030] The accompanying drawings are for illustrative purposes only; to make the technical solution of the present invention clearer, the present invention will be fully described below in conjunction with the accompanying drawings and specific embodiments. Unless otherwise specified, all reagents or instruments used are conventional products that can be purchased through market channels.

[0031] Example 1 An inorganic perovskite thin film comprising CsPbI3 and polyacrylonitrile, wherein the polyacrylonitrile content in the film is 0.005 wt%. The polyacrylonitrile in the film is used to simultaneously achieve the following functions: regulating the crystallization process, passivating defects, reducing defect state density, and reducing non-radiative recombination.

[0032] This invention provides a method for preparing inorganic perovskite thin films, comprising the following steps: (a) Add polyacrylonitrile (PAN) to a glass vial and add an appropriate amount of N,N-dimethylformamide (DMF). Place the vial on a 60°C heating plate and stir overnight to form a 0.1 mg / mL polyacrylonitrile solution.

[0033] (b) Dimethylammonium lead iodide (DMAPbI3) and cesium iodide (CsI) were dissolved in a DMF (N,N-dimethylformamide) / DMSO (dimethyl sulfoxide) mixed solution with a volume ratio of 9:1 to prepare a CsPbI3 perovskite precursor solution with a concentration of 0.7 mol / L.

[0034] (c) Add 0.05 mL of polyacrylonitrile solution from step (a) to 1 mL of CsPbI3 precursor solution prepared in step (b), mix well, and heat and stir overnight at 60°C to form a film precursor solution.

[0035] (d) The film precursor solution from step (c) was filtered through a 0.22 μm nylon filter and then spin-coated at a speed of 3000 rpm for 30 s. After spin-coating, the film was annealed in air at 200 °C for 10 min to obtain a black inorganic perovskite film.

[0036] The present invention also provides an application of an inorganic perovskite thin film in an all-inorganic perovskite solar cell, the cell comprising a transparent conductive substrate, an electron transport layer, the inorganic perovskite thin film of claim 1 as a photoactive layer, a hole transport layer, and a back electrode, which are stacked sequentially. The transparent conductive substrate is cleaned FTO conductive glass, the electron transport layer is a TiO2 layer, the hole transport layer is a Spiro-OMeTAD layer, and the back electrode is an Ag electrode.

[0037] like Figure 5As shown, the all-inorganic perovskite solar cell is fabricated by the following method: (1) Cleaning treatment of FTO: First, the FTO surface was ultrasonically cleaned with water, ethanol and isopropanol respectively, and then dried with N2. Then, it was placed in a plasma cleaner and cleaned at 50 W for 10 min to improve the hydrophilicity of the FTO surface.

[0038] (2) Fabrication of the electron transport layer (ETL): Take 2 mL of TiCl4 and dissolve it in 100 mL of deionized water. After it is completely dissolved, immerse the FTO conductive glass in the solution and then place it in a 70℃ oven for 1 h to deposit. Then take it out and wash it with deionized water and ethanol respectively. Blow dry the FTO surface with a N2 gun and place it on a 200℃ heating stage for annealing for 30 min to prepare the electron transport layer (ETL).

[0039] (3) An inorganic perovskite thin film is prepared on the electron transport layer as a photoactive layer. The preparation process is the same as the preparation method of the inorganic perovskite thin film mentioned above.

[0040] (4) Fabrication of the hole transport layer (HTL): Spiro-OMeTAD was dissolved in chlorobenzene to obtain a spin-coating solution with a concentration of 72 mg / mL. Then, 18 μL of acetonitrile solution of Li-TFSI (0.52 g / mL) and 29 μL of 4-tert-butylpyridine (tBP) were added to the photoactive layer for spin-coating at a speed of 4000 rpm for 30 s.

[0041] (5) Evaporated silver electrode: The prepared thin film was placed in a cavity with a vacuum degree of 5×10⁻⁶. -4 An Ag electrode with a deposition rate of 0.3 Å / s and a deposition thickness of 100 nm was deposited at Pa.

[0042] Comparative Example 1: No polyacrylonitrile doping.

[0043] The difference from Example 1 is that the inorganic perovskite film prepared in this example does not contain polyacrylonitrile doping in the perovskite layer. The battery prepared in this example also does not contain polyacrylonitrile doping.

[0044] Other areas not mentioned are the same as in Example 1.

[0045] like Figure 1 As shown, in Example 1 of the present invention, the film prepared by polyacrylonitrile regulation has larger and more uniform grains and fewer grain boundaries, which reduces the energy loss caused by nonradiative recombination of grain boundary defects.

[0046] like Figure 2As shown, after the perovskite film prepared by the present invention was controlled by polyacrylonitrile, the intensity of the diffraction peaks of the (110) and (220) crystal planes of the perovskite film was increased to a certain extent, which means that the crystallinity of the perovskite was improved.

[0047] like Figure 3 As shown, the thin film prepared by polyacrylonitrile regulation in this invention can passivate undercoordinated Pb. 2+ This causes the binding energy of Pb to shift towards lower binding energies.

[0048] like Figure 4 As shown, the polyacrylonitrile-doped perovskite film of the present invention exhibits a significantly stronger PL strength than the undoped perovskite film of Comparative Example 1. This is mainly attributed to the difference in PL strength between the polyacrylonitrile and Pb in the perovskite component. 2+ The strong coordination interactions between them regulate the crystallization process of perovskite and suppress the nonradiative recombination loss of charge carriers, thereby effectively increasing the internal charge carrier concentration.

[0049] The optoelectronic device prepared in Comparative Example 1 and the optoelectronic device prepared in Example 1 with added polyacrylonitrile were placed in AM1.5G, 100 mW / cm 2 The photovoltaic parameters of the device were obtained under irradiation. The data are shown in Table 1.

[0050] Table 1. Performance comparison of batteries prepared in Example 1 and Comparative Example 1 of the present invention. As can be seen from Table 1, the performance of devices doped with polyacrylonitrile is significantly improved, and the photoelectric conversion efficiency (PCE) of the all-inorganic CsPbI3 device is greater than 21%.

[0051] Combination Figure 6 As shown, the JV curves of the two devices indicate that the main reason for the performance improvement is the device's V... OC A significant improvement in FF. PCE increased by 3.56% after adjusting with polyacrylonitrile.

[0052] Example 2 A fully inorganic perovskite solar cell is fabricated as follows: (1) Cleaning treatment of FTO: The FTO conductive glass was ultrasonically cleaned sequentially with deionized water, ethanol and isopropanol, dried with N2, and then placed in a plasma cleaner for 10 minutes at 70W power.

[0053] (2) Fabrication of the electron transport layer: The cleaned FTO was immersed in a TiCl4 aqueous solution (2 mL TiCl4 dissolved in 100 mL deionized water), and deposited in a water bath at 80 °C for 1 h. Then it was washed with deionized water and ethanol, dried with N2, and annealed on a heating platform at 150 °C for 45 min to obtain a dense TiO2 electron transport layer.

[0054] (3) Preparation of inorganic perovskite thin films as photoactive layers: Polyacrylonitrile (PAN) was dissolved in N,N-dimethylformamide (DMF) and heated and stirred overnight at 60°C to form a PAN solution with a concentration of 0.5 mg / mL.

[0055] A CsPbI3 precursor solution with a concentration of 0.8 mol / L was prepared by dissolving dimethylammonium lead iodide (DMAPbI3) and cesium iodide (CsI) in a DMF / DMSO mixed solvent with a volume ratio of 9:1 at a molar ratio of 1:1.

[0056] The above PAN solution was added to the CsPbI3 precursor solution at a volume ratio of 0.05:1 (i.e., 50 μL of PAN solution was added to 1 mL of CsPbI3 precursor solution), stirred overnight at 60 °C, and filtered through a 0.22 μm nylon filter to obtain the target precursor solution.

[0057] In air, the target precursor liquid was spin-coated onto the electron transport layer at a speed of 3000 rpm for 30 seconds to form a film. Then, it was directly annealed on a heating stage at 200°C for 10 minutes to obtain a black polyacrylonitrile-modified CsPbI3 perovskite film.

[0058] (4) Preparation of the hole transport layer: Dissolve 80 mg Spiro-OMeTAD in 1 mL of chlorobenzene, add 17.5 μL of acetonitrile solution of Li-TFSI (0.52 g / mL) and 25 μL of 4-tert-butylpyridine (tBP), and stir overnight.

[0059] HTL spin-coating solution was spin-coated at 4000 rpm for 30 seconds and deposited onto the photoactive layer.

[0060] (5) Preparation of the back electrode: At a vacuum degree of 5×10 -4 Under Pa conditions, 100 nm of Ag was deposited on HTL at a rate of 0.3 Å / s as the back electrode.

[0061] Performance testing: Under standard sunlight (AM 1.5G, 100 mW / cm²), the photoelectric conversion efficiency (PCE) of this cell was measured to be 20.72%, the open-circuit voltage (Voc) to be 1.17 V, and the fill factor (FF) to be 81.8%. The unpackaged device retained 92% of its initial efficiency after being stored in air with 40% relative humidity for 500 hours.

[0062] Example 3 This embodiment 3 is basically the same as embodiment 2, except that the preparation process parameters of the perovskite layer are different, in order to demonstrate the feasibility of the process window of the present invention.

[0063] In step (3), the concentration of PAN solution was 0.2 mg / mL, and the volume ratio was 0.1:1 (100 μL of PAN solution was added to 1 mL of CsPbI3 precursor solution). The annealing temperature was 180℃, and the annealing time was 15 min.

[0064] Performance testing: The photoelectric conversion efficiency of the battery was measured to be 20.39%, the open-circuit voltage was 1.16 V, and the fill factor was 81.0%.

[0065] Example 4 This embodiment is basically the same as Embodiment 1, except that the preparation process parameters of the perovskite layer are different.

[0066] In step (3), the concentration of PAN solution was 1.0 mg / mL, and the volume ratio was 0.01:1 (10 μL of PAN solution was added to 1 mL of CsPbI3 precursor solution). The annealing temperature was 210℃, and the annealing time was 3 min.

[0067] Performance testing: The photoelectric conversion efficiency of the battery was measured to be 20.02%, the open-circuit voltage to be 1.15 V, and the fill factor to be 80.4%.

[0068] Comparative Example 2: The amount of polymer used was too high.

[0069] This comparative example is basically the same as Example 1, except that the perovskite layer preparation process is different: the concentration of PAN solution is increased to 10 mg / mL, and a volume ratio of 0.05:1 (50 μL PAN solution is added to 1 mL CsPbI3 precursor solution) is added. At this time, the mass ratio of PAN to CsI is about 0.7 g: 1 mol.

[0070] Comparative Example 3 shows that the annealing time is extended.

[0071] This comparative example is basically the same as Example 2, except that the preparation process of the perovskite layer is changed: the annealing time is extended from "10 min" to 30 min, while other conditions remain unchanged.

[0072] The batteries prepared in Examples 2-4 and Comparative Examples 2-3 were subjected to performance tests, and the results are shown in Table 2.

[0073] Table 2. Performance comparison of batteries prepared in Examples 2-4 and Comparative Examples 2-3 This invention utilizes extremely low amounts of polyacrylonitrile (PAN solution concentration 0.1-1.0 mg / mL, addition volume ratio 0.01-0.1:1) and a rapid annealing process (180-210℃, 3-15 minutes) to prepare high-efficiency all-inorganic CsPbI3 perovskite solar cells with a maximum photoelectric conversion efficiency of 21.06%.

[0074] Comparative Example 2 shows that excessive PAN content can cause the polymer to form an insulating layer, hindering carrier transport and reducing the photoelectric conversion efficiency of the battery. Comparative Example 3 shows that the rapid annealing process can prevent polymer thermal decomposition or excessive aggregation that could lead to blockage.

[0075] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. An inorganic perovskite thin film, characterized in that, The film comprises CsPbI3 and polyacrylonitrile, wherein the content of polyacrylonitrile in the film is 0.001–0.1 wt%. The polyacrylonitrile in the film is used to simultaneously achieve at least two of the following functions: regulating the crystallization process, passivating defects, reducing defect state density, and reducing non-radiative recombination.

2. The method for preparing an inorganic perovskite thin film as described in claim 1, characterized in that, Includes the following steps: (a) Dissolving polyacrylonitrile in an organic solvent to form a polyacrylonitrile solution, wherein the concentration of the polyacrylonitrile solution is 0.1 to 1 mg / mL; (b) Dissolve dimethylammonium lead iodide and cesium iodide in a mixed solvent to form a CsPbI3 precursor solution; (c) Add the polyacrylonitrile solution from step (a) to the CsPbI3 precursor solution from step (b) and mix thoroughly to form a film precursor solution; wherein, the amount of polyacrylonitrile solution added is 0.01 to 0.1 mL relative to 1 mL of CsPbI3 precursor solution. (d) Spin-coat the film precursor solution from step (c) into a film, and then anneal it in air for 3 to 15 minutes to obtain an inorganic perovskite film.

3. The method for preparing an inorganic perovskite thin film according to claim 2, characterized in that, In step (a), the organic solvent is any one or a mixture of N,N-dimethylformamide, dimethyl sulfoxide, sulfolane, and thiocyanate solution; polyacrylonitrile is added to DMF and stirred overnight on a heating table at 40-70°C.

4. The method for preparing an inorganic perovskite thin film according to claim 2, characterized in that, In step (b), the molar ratio of dimethylammonium, lead iodide, and cesium iodide is in the range of 1:0.9-1.1:0.9-1.1; the mixed solvent is a CsPbI3 perovskite precursor solution prepared by mixing DMF and DMSO at a volume ratio of 9:1 with a concentration of 0.6-1.0 mol / L.

5. The method for preparing an inorganic perovskite thin film according to claim 2, characterized in that, In step (c), after mixing evenly, the mixture is heated and stirred overnight at a temperature of 50-60°C to form a thin film precursor solution.

6. The method for preparing an inorganic perovskite thin film according to claim 2, characterized in that, In step (d), before spin coating, the film precursor solution is filtered through a 0.22 μm nylon filter head and then spin coated at a spin coating speed of 2000–4000 rpm for 20–50 s. After spin coating, the inorganic perovskite film is annealed in air at a temperature of 180–210 °C to obtain an inorganic perovskite film.

7. The application of an inorganic perovskite thin film in an all-inorganic perovskite solar cell, characterized in that, The battery comprises a transparent conductive substrate, an electron transport layer, an inorganic perovskite film as described in claim 1 or an inorganic perovskite film prepared by the method described in claims 2-6 as a photoactive layer, a hole transport layer, and a back electrode, which are stacked sequentially. The transparent conductive substrate is cleaned FTO conductive glass, the electron transport layer is a TiO2 layer, the hole transport layer is a Spiro-OMeTAD layer, and the back electrode is an Ag electrode.

8. The application according to claim 7, characterized in that, The electron transport layer is prepared by the following method: FTO conductive glass is cleaned by plasma cleaning, with a plasma cleaning power of 40-100 W and a cleaning time of 3-15 min. After cleaning, the FTO conductive glass is immersed in TiCl4 aqueous solution and deposited in a water bath at 60-90℃ for 1 hour, and then annealed at 100-200℃ for 30-60 minutes.

9. The application according to claim 7, characterized in that, The hole transport layer was prepared by the following method: Spiro-OMeTAD was dissolved in chlorobenzene to prepare a spin-coating solution with a concentration of 72-90 mg / mL, and then Li-TFSI and 4-tert-butylpyridine were added. After stirring overnight, the solution was spin-coated to form a film. The mass ratio of Spiro-OMeTAD, Li-TFSI, and 4-tert-butylpyridine is 72–90:100–200:5–20; the spin coating speed is 2000–5000 rpm, and the spin coating time is 20–40 s.

10. The application according to claim 7, characterized in that, The back electrode is formed by vapor deposition, with a vapor deposition vacuum degree of 5×10⁻⁶. -4 Pa, evaporation rate of 0.3 Å / s, thickness of 80–100 nm.

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