Low-stress perovskite thin film, preparation method thereof and application of low-stress perovskite thin film in solar cell

Abstract

The invention discloses a low-stress perovskite thin film, a preparation method thereof and application of the low-stress perovskite thin film in a solar cell. The method comprises the following steps: (1) dissolving SBMA, HEA, an initiator and raw materials for preparing a Cs0. 05FA0. 95PbI3 perovskite precursor solution in a solvent to form the perovskite precursor solution; and (2) spin-coating the perovskite precursor solution on a substrate, dropwise adding an anti-solvent diethyl ether on the substrate before spin-coating is finished, and performing annealing treatment to form the low-stress perovskite thin film. Two monomers and an initiator are added into a perovskite precursor solution, and the two monomers are subjected to in-situ copolymerization during annealing, so that large-size grains and better crystallization orientation are formed. In addition, the polymer formed by copolymerization has relatively low Tg, so that the polymer is in a soft elastic state in the annealing process of the perovskite thin film, and the stress in the perovskite thin film can be effectively released. Therefore, the performance and the stability of the perovskite solar cell are effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a low-stress perovskite thin film, its preparation method, and its application in solar cells. Background Technology

[0002] Metal halide perovskite solar cells (PSCs), as a new generation of photovoltaic power generation technology, have achieved a power conversion efficiency (PCE) exceeding 26.1%, attracting widespread attention. This significant progress is mainly attributed to continuous efforts in device optimization, compositional engineering, defect passivation, and the development of carrier transport materials. However, the unavoidable residual strain in polycrystalline perovskite materials leads to unnecessary energy losses within PSCs, limiting further breakthroughs in PCE. Strain in perovskite thin films primarily originates from two sources: 1) internal stresses caused by ideal structural distortions and 2) external stresses resulting from thermal expansion coefficient (CTE) mismatch and epitaxial lattice mismatch. These stresses alter the band structure, carrier mobility, ion migration activation energy, and defect formation energy of the perovskite material, thereby affecting the performance and stability of PSCs.

[0003] To mitigate the impact of adverse stresses on the performance and stability of perovskite films (PSCs), various attempts have been made to modulate stress in perovskite films. During thermal annealing and cooling, external stresses accumulate in the perovskite film due to the difference in charge transfer efficiency (CTE) between the perovskite layer and the substrate. Therefore, modifying the annealing process (e.g., room temperature fabrication) or introducing contact layers with higher CTEs (e.g., polycarbonate) are effective methods to reduce tensile stress during fabrication. However, these strategies often result in low-quality perovskite films and lower carrier collection, thus degrading device performance. Therefore, some studies have introduced interface layers to alleviate stress concentration during perovskite growth, thereby significantly improving device performance and stability.

[0004] Furthermore, to regulate the internal stress caused by local lattice distortion, organic molecular additives are introduced into perovskite films to stabilize the α phase and suppress internal stress. Unlike small molecule additives, which suffer from poor stability, uneven distribution, and limited number of functional groups, polymer additives have attracted considerable attention due to their good stability, numerous functional groups, and excellent structural designability. Additionally, the inherent flexibility and stress absorption capacity of polymers allow for significant stress relief when introduced into perovskite films. However, previously reported polymer additives typically exhibit high glass transition temperatures (T0). g The annealing temperature of the polymer in perovskite films even exceeds the annealing temperature of perovskite films (100-150℃). When perovskite films are annealed, the polymer remains in a hard and brittle glassy state, and stress cannot be effectively released during film formation. Therefore, the existing technology requires further improvement and development. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing low-stress perovskite thin films by utilizing in-situ copolymerization to alleviate the stress generated during the annealing of perovskite thin films, and a perovskite solar cell.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing low-stress perovskite thin films.

[0007] The method for preparing low-stress perovskite films by in-situ copolymerization to regulate the stress of perovskite films provided by the present invention includes the following steps: (1) 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt (SBMA), hydroxyethyl acrylate (HEA), initiator, and preparation of Cs 0.05 FA 0.95 The raw materials for the PbI3 perovskite precursor solution are dissolved in a solvent and stirred at room temperature to form the perovskite precursor solution. (2) Preparation of perovskite thin films by one-step spin coating: The perovskite precursor solution is spin-coated onto the substrate. Before spin coating is completed, diethyl ether, the antisolvent, is dropped onto the substrate, followed by annealing to form a low-stress perovskite film.

[0008] During the annealing process described above, SBMA and HEA can undergo in-situ copolymerization to form a low-T... g The polymer is designed to exhibit a soft and elastic state at the annealing temperature, effectively releasing the stress inside the perovskite film and thus obtaining a low-stress perovskite film.

[0009] In step (1) of the above method, the concentration of HEA in the perovskite precursor solution is 0.01~5 mg / mL, preferably 0.05~1 mg / mL.

[0010] In step (1) of the above method, the ratio of SBMA to HEA is 4:1 to 1:4 (molar ratio), specifically 4:1, 3:2, 2:3, 1:4, with 3:2 being the optimal ratio.

[0011] In step (1) of the above method, the initiator is at least one of ammonium persulfate, potassium persulfate and sodium persulfate.

[0012] In step (1) of the above method, the concentration of the initiator in the perovskite precursor solution is 0.025 mg / mL.

[0013] In step (1) of the above method, the preparation of Cs 0.05 FA0.95 The raw materials for the PbI3 perovskite precursor solution include: formamidinium hydroiodide (FAI), CsI, PbI2, and methylammonium chloride (MACl); the mass ratio of FAI, CsI, PbI2, and MACl is 13:1:40:1.8.

[0014] In step (1) of the above method, the solvent is a mixed solvent obtained by mixing DMF and DMSO in a volume ratio of 4:1 to 10:1 (specifically 8:1).

[0015] In step (2) of the above method, the substrate can be an ITO glass substrate.

[0016] In step (2) of the above method, the antisolvent diethyl ether is added 10-20 s before the end of spin coating, preferably 20 s.

[0017] In step (2) of the above method, the annealing temperature is 100-150 degrees Celsius and the annealing time is 30-60 minutes.

[0018] In the above method, an electron transport layer (such as a SnO2 layer) is also provided on the substrate.

[0019] According to one embodiment of the present invention, a perovskite precursor solution (60 μL) is spin-coated onto the surface of the SnO2 electron transport layer in two consecutive spin-coating steps, specifically spin-coating at 1000 rpm for 10 s and at 5000 rpm for 30 s. At 20 s before the end of spin-coating, diethyl ether (400 μL) is rapidly dropped onto the substrate as an antisolvent.

[0020] The low-stress perovskite thin films prepared by the above method are also within the scope of protection of this invention.

[0021] Secondly, the present invention provides the application of the low-stress perovskite thin film in the fabrication of perovskite solar cells.

[0022] Thirdly, the present invention provides a perovskite solar cell containing the aforementioned low-stress perovskite thin film.

[0023] The perovskite solar cell provided by the present invention includes the low-stress perovskite thin film described above.

[0024] Furthermore, the perovskite solar cell specifically includes a cathode, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and an anode arranged sequentially, wherein the perovskite light-absorbing layer is a low-stress perovskite thin film prepared by the method described above.

[0025] The cathode material is selected from either indium tin oxide (ITO) thin film or fluorine-doped SnO2 (FTO) thin film.

[0026] The electron transport layer is made of either titanium oxide (TiO2) or tin oxide (SnO2).

[0027] The material of the hole transport layer is selected from 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA).

[0028] The anode is made of either gold (Au) or silver (Ag).

[0029] Fourthly, the present invention provides a method for preparing a perovskite solar cell according to the third aspect of the present invention.

[0030] The method for preparing a perovskite solar cell provided by this invention includes the following steps: (a) Fabrication of an electron transport layer on a cathode substrate; (b) A perovskite light-absorbing layer is prepared by spin-coating on the electron transport layer; (c) A hole transport layer is prepared on the perovskite light-absorbing layer; (d) An anode is fabricated on the hole transport layer to obtain the perovskite solar cell.

[0031] Step (a) of the above method can prepare a SnO2 electron transport layer on an ITO glass substrate. According to an embodiment of the present invention, the specific preparation method is as follows: a SnO2 solution (3wt.%) is spin-coated onto the treated ITO glass at a speed of 4000 rpm for 30 s, and then annealed on a hot stage at 150 ℃ for 30 min to form a SnO2 electron transport layer.

[0032] In step (b) of the above method, the method for spin-coating the perovskite light-absorbing layer on the electron transport layer can be carried out according to the method described in the first aspect of the present invention.

[0033] After step (b) and before step (c), there is also a step of passivating the perovskite light-absorbing layer prepared in step (b), specifically as follows: spin-coating 4-MeOPEAI solution onto the perovskite light-absorbing layer, and then annealing the perovskite light-absorbing layer at 100 °C for 5 min to passivate the perovskite light-absorbing layer.

[0034] According to an embodiment of the present invention, 4-MeOPEAI was dissolved in isopropanol (3 mg / mL); 100 μL of 4-MeOPEAI solution was spin-coated onto the perovskite light-absorbing layer at 4000 rpm for 30 s, and then the perovskite light-absorbing layer was annealed at 100 °C for 5 min to passivate the perovskite light-absorbing layer.

[0035] In step (c) of the above method, the hole transport layer is a 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD) layer. According to one embodiment of the present invention, the specific preparation method is as follows: a Spiro-OMeTAD solution of a certain concentration is spin-coated onto a perovskite light-absorbing layer at a rotation speed of 4000 rpm for 30 s to form a Spiro-OMeTAD hole transport layer. The Spiro-OMeTAD solution comprises 72.3 mg Spiro-OMeTAD, 17.5 μL of lithium bis(trifluoromethane)sulfonylimide (Li-TFSI) solution (520 mg Li-TFSI dispersed in 1 mL acetonitrile), 28.8 μL of 4-tert-butylpyridine, and 1000 μL of chlorobenzene.

[0036] In step (d) of the above method, an anode is prepared on the hole transport layer by vacuum evaporation.

[0037] Compared with the prior art, the present invention has the following beneficial effects: This invention introduces two monomers (SBMA and HEA) and an initiator into a perovskite precursor solution, followed by in-situ copolymerization of the two monomers during perovskite annealing. This results in large-sized grains and improved crystal orientation. Furthermore, the copolymerized polymer exhibits a low Tg, allowing it to remain in a soft, elastic state during perovskite film annealing, effectively releasing internal stresses. This significantly improves the performance and stability of perovskite solar cells. Attached Figure Description

[0038] Figure 1 This is the structural formula of SBMA and HEA described in this invention.

[0039] Figure 2 This is a scanning electron microscope comparison image of the surface of the standard perovskite film prepared in Comparative Example 1 and the low-stress perovskite film prepared in Example 1.

[0040] Figure 3 The image shows a comparison of the X-ray photoelectron spectra of the standard perovskite film prepared in Comparative Example 1 and the low-stress perovskite film prepared in Example 1.

[0041] Figure 4 The image shows a comparison of slightly incident X-ray diffraction patterns of the standard perovskite film prepared in Comparative Example 1 and the low-stress perovskite film prepared in Example 1.

[0042] Figure 5This invention compares the standard perovskite film prepared in Comparative Example 1 with the low-stress perovskite film prepared in Example 1. Figure 4 The linear fitting comparison chart.

[0043] Figure 6 This is a comparison image of peak force quantitative nanomechanics atomic force microscopy between the standard perovskite film prepared in Comparative Example 1 and the low-stress perovskite film prepared in Example 1 of the present invention.

[0044] Figure 7 The JV curves are shown for the standard perovskite solar cell prepared in Comparative Example 1 and the low-stress perovskite solar cell prepared in Example 1 of this invention.

[0045] Figure 8 This is a comparison diagram of the photostability of the standard perovskite solar cell prepared in Comparative Example 1 and the low-stress perovskite solar cell prepared in Example 1.

[0046] Figure 9 This is a comparison diagram of the thermal stability of the standard perovskite solar cell prepared in Comparative Example 1 and the low-stress perovskite solar cell prepared in Example 1.

[0047] Figure 10 This is a comparison diagram of the water droplet contact angle between the standard perovskite thin film prepared in Comparative Example 1 and the low-stress perovskite solar cell thin film prepared in Example 1. Detailed Implementation

[0048] The present invention will now be described in further detail with reference to specific embodiments. The given embodiments are merely illustrative of the invention and not intended to limit its scope. The embodiments provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation on the invention in any way.

[0049] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0050] Comparative Example 1 The method for fabricating a perovskite solar cell in this embodiment includes the following steps: (1) The ITO glass was ultrasonically cleaned with water, acetone and isopropanol for 15 min in sequence. After cleaning, it was dried with a nitrogen gun and then placed in a plasma cleaner for ultraviolet ozone treatment for 10 min.

[0051] (2) The SnO2 precursor (15 wt.% SnO2 solution) was diluted with water (SnO2: H2O = 1:4, v / v) to obtain a SnO2 solution (3 wt.%). The SnO2 solution was spin-coated onto the treated ITO glass at a speed of 4000 rpm for 30 s. The glass was then annealed at 150 ℃ for 30 min on a hot plate to form a SnO2 electron transport layer, denoted as ITO / SnO2.

[0052] (3) Before depositing the perovskite film, ITO / SnO2 was treated with UV ozone in a plasma cleaner for 10 min and then transferred to a nitrogen-environment glove box. FAI (240.76 mg), CsI (18.19 mg), PbI2 (728.40 mg), and MACl (33.08 mg) powders were dissolved in 1 mL of DMF / DMSO (8:1, v / v) mixed solvent and stirred overnight at room temperature to form a perovskite precursor solution. The perovskite precursor solution (60 μL) was spin-coated onto the surface of the SnO2 electron transport layer in two consecutive spin-coating steps: spin-coating at 1000 rpm for 10 s and at 5000 rpm for 30 s. 20 s before the end of spin-coating, 400 μL of diethyl ether was rapidly dropped onto the perovskite film as an antisolvent. After spin coating, the film was annealed at 120 °C and 25% RH for 1 hour to form a standard perovskite film.

[0053] (4) Dissolve 4-MeO-PEAI in isopropanol (3 mg / mL). Spin-coat the MeO-PEAI solution (100 μL) onto a standard perovskite film at 4000 rpm for 30 s, and then passivate the perovskite film by annealing at 100 °C for 5 min.

[0054] (5) The Spiro-OMeTAD solution was spin-coated onto the perovskite layer at a speed of 4000 rpm for 30 s, and the prepared sample was oxidized in a desiccator for 10 h. The Spiro-OMeTAD solution consisted of 72.3 mg Spiro-OMeTAD, 17.5 μL of lithium bis(trifluoromethane)sulfonylimide (Li-TFSI) solution (520 mg Li-TFSI dispersed in 1 mL acetonitrile), 28.8 μL of 4-tert-butylpyridine, and 1000 μL of chlorobenzene.

[0055] (6) Finally, in a vacuum coating machine, through thermal evaporation (<2.5×10 -4 An 80 nm Au electrode was deposited using Pa to obtain a perovskite solar cell.

[0056] Example 1 The difference between this embodiment and Comparative Example 1 is that step (3) is different, while the other steps are the same as those in Comparative Example 1.

[0057] (1) The ITO glass was ultrasonically cleaned with water, acetone and isopropanol for 15 min in sequence. After cleaning, it was dried with a nitrogen gun and then placed in a plasma cleaner for ultraviolet ozone treatment for 10 min.

[0058] (2) The SnO2 precursor (15 wt.% SnO2 solution) was diluted with water (SnO2: H2O = 1:4, v / v) to obtain a SnO2 solution (3 wt.%). The SnO2 solution was spin-coated onto the treated ITO glass at a speed of 4000 rpm for 30 s. The glass was then annealed at 150 ℃ for 30 min on a hot plate to form a SnO2 electron transport layer, denoted as ITO / SnO2.

[0059] (3) Before depositing the perovskite film, ITO / SnO2 was placed in a plasma cleaner and treated with ultraviolet ozone for 10 min, and then transferred to a nitrogen-environment glove box. FAI (240.76 mg), CsI (18.19 mg), PbI2 (728.40 mg), MACl (33.08 mg), SBMA (0.5 mg), HEA (0.14 mg) (SBMA:HEA = 3:2, molar ratio) and ammonium persulfate (0.025 mg) were dissolved in 1 mL of DMF / DMSO (8:1, v / v) mixed solvent and stirred overnight at room temperature to form a perovskite precursor solution. The perovskite precursor solution (60 μL) was spin-coated onto the surface of the SnO2 electron transport layer in two consecutive spin-coating steps: spin-coating at 1000 rpm for 10 s and at 5000 rpm for 30 s. Twenty s before the end of spin-coating, 400 μL of diethyl ether was rapidly dropped onto the perovskite film as an antisolvent. After spin-coating, the film was annealed at 120 °C and 25% RH for 1 hour to form a low-stress perovskite film.

[0060] (4) Dissolve 4-MeO-PEAI in isopropanol (3 mg / mL). Spin-coat the MeO-PEAI solution (100 μL) onto the low-stress perovskite film at 4000 rpm for 30 s, and then passivate the perovskite film by annealing at 100 °C for 5 min.

[0061] (5) The Spiro-OMeTAD solution was spin-coated onto the perovskite layer at a speed of 4000 rpm for 30 s, and the prepared sample was oxidized in a desiccator for 10 h. The Spiro-OMeTAD solution consisted of 72.3 mg Spiro-OMeTAD, 17.5 μL of lithium bis(trifluoromethane)sulfonylimide (Li-TFSI) solution (520 mg Li-TFSI dispersed in 1 mL acetonitrile), 28.8 μL of 4-tert-butylpyridine, and 1000 μL of chlorobenzene.

[0062] (6) Finally, in a vacuum coating machine, through thermal evaporation (<2.5×10 -4 An 80 nm Au electrode was deposited using Pa to obtain a perovskite solar cell.

[0063] See Figure 1 The molecular structures of SBMA and HEA are shown.

[0064] See Figure 2 The images show scanning electron microscope (SEM) surface images of a standard perovskite film and a low-stress perovskite film. It can be seen that the grain size of the low-stress perovskite film is significantly larger than that of the standard perovskite film, and there is no residual PbI2. This indicates that during perovskite annealing, the in-situ copolymerization of SBMA and HEA molecules merges small grains into larger grains, greatly promoting perovskite growth. The reduced PbI2 on the perovskite film surface can be attributed to the interaction between the polymer and PbI2.

[0065] See Figure 3 X-ray photoelectron spectroscopy analysis of standard perovskite films and low-stress perovskite films is presented. It can be seen that compared to the standard film, the Pb 4f and I 3d peaks of the low-stress film are shifted to lower binding energies, indicating an interaction between Pb, I, and the polymer, thereby passivating defects.

[0066] See Figure 4 This study presents stress analyses for standard and low-stress perovskite films. Residual tensile stress in perovskite films significantly impacts the efficiency and stability of perovskite solar cells. Therefore, 2θ-sinψ is used. 2 The method utilizes grazing incidence X-ray diffraction (GIXRD) to study the stress in perovskite thin films. Stress analysis of the (012) crystal plane at 31.6° revealed that for the standard film, the 2θ corresponding to the (012) diffraction peak gradually decreases with increasing ψ value, indicating a gradual increase in interplanar spacing. However, for the low-stress film, the 2θ corresponding to the (012) diffraction peak remains essentially unchanged with increasing ψ value, indicating that the interplanar spacing remains essentially constant, suggesting the existence of lower residual tensile stress in the low-stress film.

[0067] See Figure 5 In order to Figure 4 Perform 2θ-sinψ 2 Linear fitting allows the magnitude of residual stress to be represented by the slope of the fitted line. A lower slope indicates greater residual stress in the film. Figure 5 As can be seen, the slope of the low-stress film is significantly smaller than that of the standard film, indicating that there is lower residual tensile stress in the low-stress film. See Figure 6 The image shows a comparison of peak force quantitative nanomechanical atomic force microscopy (PFQNM) results for a standard perovskite film and a low-stress perovskite film. It can be seen that the low-stress film exhibits a lower Young's modulus, indicating higher mechanical bending properties.

[0068] See Figure 7 Table 1 shows the reverse and forward scan JV characteristics of the standard optimal device and the low-stress optimal device. The optimal device fabricated with low-stress thin film exhibits a conversion efficiency of 25.70% and a short-circuit current of 25.67 mA cm⁻¹. -2 The open-circuit voltage is 1.194 V and the fill factor is 83.85%. This is higher than the best device prepared with standard thin films (conversion efficiency of 23.52% and short-circuit current of 25.39 mA cm⁻¹). -2 (The open-circuit voltage is 1.178 V and the fill factor is 78.67%). Furthermore, the results of forward and reverse scans show that the hysteresis of the low-stress device is negligible.

[0069] Table 1. Performance Comparison of Standard Devices and Low-Stress Devices (Reverse Scan)

[0070] See Figure 8 This study investigated the optical stability of standard and low-stress devices. It shows that under continuous solar irradiation in an N2 environment for 1000 hours, the low-stress device retains 93.8% of its initial efficiency, while the standard device only retains 72.1%.

[0071] See Figure 9 This study investigated the thermal stability of standard and low-stress devices. It shows that in an N2 environment at 85 °C, after 500 h, the low-stress device still maintained 90.6% of its initial efficiency, while the standard device only maintained 70.3%.

[0072] See Figure 10The figure shows a comparison of the water contact angles of a standard perovskite film and a low-stress perovskite film. It can be seen that the low-stress perovskite film has a larger water contact angle (73.0°) than the standard perovskite film (56.2°), indicating that the low-stress perovskite film has better hydrophobicity, which is beneficial to improving the stability of the device.

[0073] Example 2 The difference between this embodiment and Embodiment 1 is that: The ratio of SBMA to HEA in step (3) was adjusted to 4:1, 2:3 and 1:4 (molar ratio), and the remaining steps were the same as in Example 1.

[0074] Table 2. Performance Comparison of Devices Fabricated at Different SBMA:HEA Ratios (Reverse Scan)

[0075] Table 2 shows a performance comparison of perovskite solar cells prepared with different SBMA:HEA ratios. It can be seen that the device with the best performance is prepared when the SBMA:HEA ratio is 3:2.

[0076] In summary, this invention proposes using both SBMA and HEA as additives for perovskite thin films. The two monomers can achieve in-situ copolymerization and fill perovskite grain boundaries as a scaffold, effectively stabilizing the α-phase perovskite. The resulting copolymer possesses the ability to coordinate with PbI2, which is crucial for regulating the crystallization and passivating trap states of the perovskite. Furthermore, the copolymer exhibits a lower Tg. g This allows the polymer to exhibit a soft, elastic state during the annealing process of the perovskite film, effectively releasing the stress within the perovskite film. Therefore, the PCE of PSCs based on SBMA / HEA is 25.70%. Furthermore, under continuous illumination, the unencapsulated device maintained 93.8% of its initial efficiency within 1000 hours.

[0077] The present invention has been described in detail above. For those skilled in the art, the invention can be practiced in a wide range of ways with equivalent parameters, concentrations, and conditions without departing from its spirit and scope, and without requiring unnecessary experiments. Although specific embodiments have been given, it should be understood that further modifications can be made to the invention. In summary, according to the principles of the invention, this application is intended to include any changes, uses, or improvements to the invention, including changes made using conventional techniques known in the art that depart from the scope disclosed herein. Some of the essential features can be applied within the scope of the following appended claims.

Claims

1. A method for preparing low-stress perovskite thin films, comprising the following steps: (1) 3-[N,N-dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]ammonium]propane-1-sulfonic acid inner salt (SBMA), hydroxyethyl acrylate (HEA), initiator, and preparation of Cs 0.05 FA 0.95 The raw materials for the PbI3 perovskite precursor solution are dissolved in a solvent and stirred at room temperature to form the perovskite precursor solution. (2) Preparation of perovskite thin films by one-step spin coating: The perovskite precursor solution is spin-coated onto the substrate. Before spin coating is completed, diethyl ether, the antisolvent, is dropped onto the substrate, followed by annealing to form a low-stress perovskite film.

2. The preparation method according to claim 1, characterized in that: In step (1), the concentration of HEA in the perovskite precursor solution is 0.01~5 mg / mL, preferably 0.05~1 mg / mL; And / or, in step (1), the molar ratio of SBMA to HEA is 4:1 to 1:4; And / or, in step (1), the initiator is at least one of ammonium persulfate, potassium persulfate and sodium persulfate.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the preparation of Cs 0.05 FA 0.95 The raw materials for the PbI3 perovskite precursor solution include: formamidin hydroiodide (FAI), CsI, PbI2, and methylammonium chloride (MACl), wherein the mass ratio of FAI, CsI, PbI2, and MACl is 13:1:40:1.

8. And / or, in step (1), the solvent is a mixed solvent obtained by mixing DMF and DMSO in a volume ratio of 4:1 to 10:

1.

4. The preparation method according to any one of claims 1-3, characterized in that: In step (2), the antisolvent diethyl ether is added 10-20 seconds before the spin coating ends, preferably 20 seconds.

5. The preparation method according to any one of claims 1-4, characterized in that: In step (2), the annealing temperature is 100-150 degrees Celsius and the annealing time is 30-60 minutes.

6. The low-stress perovskite thin film prepared by the method according to any one of claims 1-5.

7. A perovskite solar cell comprising the low-stress perovskite thin film as described in claim 6.

8. The perovskite solar cell according to claim 7, characterized in that: The perovskite solar cell comprises a cathode, an electron transport layer, a perovskite light-absorbing layer, a hole transport layer, and an anode arranged sequentially, wherein the perovskite light-absorbing layer is the low-stress perovskite thin film as described in claim 6.

9. The perovskite solar cell according to claim 8, characterized in that: The cathode material is selected from either indium tin oxide (ITO) thin film or fluorine-doped SnO2 (FTO) thin film; The electron transport layer is made of either titanium oxide (TiO2) or tin oxide (SnO2). The material of the hole transport layer is selected from 2,2',7,7'-tetratetra[N,N-di(4-methoxyphenyl)amino]-9,9'-spirodifluorene (Spiro-OMeTAD) and poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine (PTAA); The anode is made of either gold (Au) or silver (Ag).

10. A method for preparing a perovskite solar cell according to any one of claims 7-9, comprising the following steps: (a) Fabrication of an electron transport layer on a cathode substrate; (b) A perovskite light-absorbing layer is prepared by spin-coating on the electron transport layer; (c) A hole transport layer is prepared on the perovskite light-absorbing layer; (d) An anode is fabricated on the hole transport layer to obtain the perovskite solar cell.

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