Perovskite solar cell and preparation method thereof

Abstract

According to the perovskite solar cell and the preparation method thereof provided by the invention, the additive is introduced into the perovskite layer, so that the additive and FAI can form strong hydrogen-bond interaction, the crystallization process in the perovskite layer is regulated and controlled, and more uniform concentration and distribution of PbI2 in the perovskite layer are realized, thereby improving the crystallization quality and morphology uniformity of the perovskite layer. And secondly, the additive has reducibility, so that the possibility that PbI2 is decomposed into Pb and I2 in the crystallization process is effectively inhibited. In addition, the additive can significantly promote directional migration of residual PbI2 in a perovskite body phase to a grain boundary and enrichment in a grain boundary region. The distribution optimization of the PbI2 in the bulk phase and the grain boundary can play double roles: on one hand, by passivating the grain boundary defects, the grain boundary defect density is effectively reduced, and the non-radiative recombination center is reduced; and on the other hand, the enriched PbI2 further stabilizes the grain boundary structure and optimizes the crystal arrangement, thereby further improving the overall morphology and carrier transport performance of the perovskite layer.

Description

Technical Field

[0001] The present invention relates to the field of solar cells, and in particular to a perovskite solar cell and a preparation method thereof. Background Art

[0002] Perovskite materials have made great achievements in the field of optoelectronics. At present, the most advanced perovskite solar cell devices have achieved a certified power conversion efficiency of 26.7% and are considered to be the next generation of photovoltaic technology. Despite such great progress, perovskite materials still face a series of challenges in the preparation process. The perovskite precursor solution is prone to rapid crystallization during the film formation process, which can lead to small grain size, increased number of grain boundaries, and increased roughness of the film surface, which can easily induce non-radiative recombination and reduce carrier transfer efficiency, significantly reducing the carrier transfer efficiency and the optoelectronic performance of perovskite solar cells. Summary of the invention

[0003] In order to solve the above technical problems, the first aspect of the present invention provides a perovskite solar cell, which includes a conductive substrate layer, a hole transport layer, a perovskite layer, an electron transport layer, a buffer layer and an electrode in the direction of evaporation thickness, wherein the perovskite layer contains methyl hydrazinethiohydrazinecarboxylate hydroiodide for modifying the perovskite; the structural formula of methyl hydrazinethiohydrazinecarboxylate is The general structural formula of perovskite is ABX3, wherein A is a metal cation and / or an alkylammonium salt, B is a divalent metal cation, and C is a halogen anion; and A includes NH2CHNH2 + , B includes Pb 2+ , C includes I - , so that the perovskite contains components FAI and PbI2.

[0004] In the present invention, the additive methyl hydrazinethiohydrazinecarboxylate hydroiodide can improve the crystallization quality and morphology uniformity of the perovskite layer; effectively inhibit the possibility of PbI2 decomposing into Pb and I2 during the crystallization process; and can also significantly promote the directional migration of residual PbI2 in the perovskite bulk phase to the grain boundary and enrich it in the grain boundary region, thereby effectively reducing the grain boundary defect density and reducing non-radiative recombination centers; and the enriched PbI2 further stabilizes the grain boundary structure and optimizes the crystal arrangement, thereby improving the overall morphology and carrier transport performance of the perovskite layer.

[0005] Furthermore, A also includes Cs + , K + , Rb + and / or CH3NH3 + etc. metal cations or alkylammonium salts, B also includes Cu 2 + 、Ni 2+ 、Co2+ 、Cd 2+ ,Ge 2+ and / or Sn 2+ divalent metal cations, X also includes Br - and / or Cl - Halogen anions such as halogen anions. In addition to the components FAI and PbI2, the perovskite may also include other AX and BX2 components. Although the components of the perovskites in different embodiments are different, the additives introduced in the present invention can be used to improve the crystal quality of the perovskite layer and effectively optimize the spatial distribution of PbI2, so that compared with the perovskite solar cell device without the introduction of additives, the stability and charge transfer efficiency of the perovskite solar cell device of the present invention can be improved.

[0006] The second aspect of the embodiment of the present invention provides a method for preparing a perovskite solar cell, the preparation method comprising: step S1, cleaning: cleaning a conductive substrate to obtain a conductive base layer; step S2, preparing a hole transport layer: using a 4PADCB solution to spin-coat and anneal the cleaned conductive substrate to obtain a first film; step S3, preparing a first precursor solution: dissolving an AX solid and a BX2 solid in a mixed solvent of DMF and DMSO to obtain a first precursor solution; wherein AX includes but is not limited to FAI, and BX2 includes but is not limited to PbI2; step S4, preparing a second precursor solution: adding a hydrazinothiohydrazinecarboxylic acid methyl ester hydroiodide solid to the prepared first precursor solution, stirring to fully react, and obtaining a second precursor solution; step S5, preparing a perovskite layer: spin-coating the second precursor solution on the first film, and before the spin-coating procedure ends, dripping a CB anti-solvent, and then annealing to obtain a second film; step S6, preparing an electron transport layer: dissolving PCBM and C 60 Dissolved in a mixed solvent of CB and IPA, and spin-coated on the second film, and then evaporated C 60 , obtaining a third film; step S7, preparing a buffer layer: evaporating BCP on the third film to obtain a fourth film; step S8, preparing an electrode: evaporating an electrode on the fourth film, and finally obtaining a perovskite solar cell device containing the additive methyl hydrazinothiohydrazinecarboxylate hydroiodide.

[0007] In the present invention, a second precursor solution is obtained by adding a hydrazinethiohydrazinecarboxylic acid methyl ester hydroiodide solid to the first precursor solution, and the second precursor solution is spin-coated on the first film, so that the perovskite layer on the first film has additive modification. In addition, the perovskite layer also includes components FAI and BX2. The additive is enabled to form a strong hydrogen bond with FAI, and the additive suppresses the rapid generation of non-uniform nuclei by regulating the formation and growth dynamics of the perovskite layer nucleus, prolongs the crystallization time window, and promotes the orderly growth of crystals. The present invention prepares a perovskite layer with a larger grain size and better crystallinity, significantly reduces the grain boundary defect density, thereby improving the life span and mobility of carriers. In addition, the introduction of the additive effectively optimizes the spatial distribution of PbI2 during the crystallization regulation process. By slowing down the crystallization rate, the residual PbI2 is directed to migrate to the grain boundary from the bulk phase of the perovskite layer, forming a more uniform and optimized PbI2 distribution. The PbI2 enriched at the grain boundaries not only plays a role in grain boundary passivation, but also further improves the stability and charge transfer efficiency of perovskite solar cell devices.

[0008] According to the method of the present invention, in step S1, the conductive base layer can be pretreated by any method in the art. Exemplarily, the conductive substrate can be ultrasonically cleaned 1 to 3 times using detergent, deionized water, ethanol, isopropanol, etc., and each cleaning time can be 10 to 20 minutes. Exemplarily, the conductive substrate can be ITO or IWO, etc. Preferably, the conductive substrate after ultrasonic cleaning can also be treated with an ozone-ultraviolet surface cleaner for 10 to 20 minutes.

[0009] According to the method of the present invention, in step S2, illustratively, 0.1-1 mg / ml of 4PADCB ([4-(7H-dibenzocarbazole-7-yl)butyl]phosphoric acid of chemical formula C) can be added to a glove box filled with an inert gas. 24 H 22 NO3P) solution (the solvent is generally an organic solvent such as CH3OH) is spin-coated on the cleaned conductive substrate, the spin-coating speed is generally 3500~5000rpm, and the spin-coating time is generally 35~45s; so that the hole transport layer is covered on the conductive base layer; after the spin-coating is completed, annealing can be performed, the annealing time is generally 3~8min, and the annealing temperature is generally 100~200℃ to obtain the first film, which can be named ITO / 4PADCB film. Preferably, an organic solvent such as IPA (isopropyl alcohol, chemical formula C3H8O) can also be used to spin-coat the ITO / 4PADCB film at a spin-coating speed of 4000~5000rpm and a spin-coating time of 20~50s to clean the ITO / 4PADCB film. Preferably, the inert gas in the glove box can use any known inert gas, including but not limited to nitrogen, argon, etc.

[0010] According to the method of the present invention, in step S3, the AX solid and the BX2 solid can be components of perovskite, and A includes but is not limited to NH2CHNH2 + , B includes but is not limited to Pb 2+ , C includes but is not limited to I - , so that AX includes but is not limited to FAI, and BX2 includes but is not limited to PbI2. In step S3, preferably, the molar ratio of AX solid to BX2 solid is 1:(1-1.4). More preferably, the molar ratio of AX to BX2 can be 1:1, 1:1.02, 1:1.05, 1:1.07, 1:1.1, 1:1.12, 1:1.15, 1:1.17, 1:1.2, 1:1.22, 1:1.25, 1:1.27, 1:1.3, 1:1.32, 1:1.35, 1:1.37 or 1:1.4, etc. Preferably, in step S2, the volume fraction ratio of DMF (N,N-dimethylformamide, chemical formula C3H7NO) is X, and the volume fraction ratio of DMSO (dimethyl sulfoxide, chemical formula C2H6OS) is Y, wherein X is 75% to 100%, and Y=1-X. Exemplarily, X can be 75%, 80%, 85%, 90%, 95% or 100%, etc., and Y is adaptively adjusted. Although the components of the perovskite in different embodiments are different, and even the contents of different components are different, or the volume fraction ratio of DMF and DMSO is different, the stability and charge transfer efficiency of the perovskite solar cell device of the present invention can be improved compared to the perovskite solar cell device without the introduction of additives, which will not be elaborated here. Preferably, AX consists of MACl (methylamine hydrochloride, chemical formula CH6ClN), CsI, MAI (methylamine hydroiodide, chemical formula CH6IN), MABr (methylamine hydrobromide, chemical formula CH6BrN) and FAI, and BX2 consists of PbBr2 and PbI2.

[0011] According to the method of the present invention, in step S4, preferably, the first precursor solution is Xml, the methyl hydrazinothiohydrazone hydroiodide solid is Ymg, and X:Y can be 10:(1-5). Exemplarily, the volume of the first precursor solution can be 1ml, and the mass of the methyl hydrazinothiohydrazone hydroiodide solid can be 0.1mg, 0.2mg, 0.3mg, 0.4mg or 0.5mg, etc.

[0012] It should be noted that the additive in the present invention is methylhydrazine-1-carbohydrazonothioate hydroiodide; the first precursor solution is a perovskite precursor solution without the additive, and the second precursor solution is a precursor solution with the additive.

[0013] According to the method of the present invention, in step S5, preferably, the second precursor solution can be spin-coated on the ITO / 4PADCB film at two different spin-coating speeds. Preferably, the first spin-coating speed is 800-1200rpm, and the spin-coating time is 5-15s; the second spin-coating speed is 3000-4000rpm, and the spin-coating time is 30-40s. More preferably, the first spin-coating speed is 1000rpm, and the spin-coating time is 10s; the second spin-coating speed is 3000-4000rpm, and the spin-coating time is 35s. Exemplarily, the second spin-coating speed can be 3000rpm, 3200rpm, 3500rpm, 3800rpm or 4000rpm, etc. Preferably, 100-200μL CB anti-solvent can be added 8-20s before the end of the spin-coating procedure, and annealed at 80-150°C for about 10-50min. More preferably, the annealing temperature in step 5 may be 100° C. and the annealing time may be 20 to 40 minutes. Exemplarily, the annealing time may be 20 minutes, 25 minutes, 30 minutes, 35 minutes or 40 minutes, etc. By spin coating the second precursor solution with the additive introduced on the ITO / 4PADCB film, the hole transport layer is covered with the perovskite layer with the additive introduced to obtain the second film, which may be named ITO / 4PADCB / PVSK film.

[0014] In step S6, preferably, CB (chlorobenzene, chemical formula C3H8O) solvent and IPA (isopropyl alcohol, chemical formula C3H8O) solvent can be mixed at a volume fraction ratio of 0.5 to 2 to form a mixed solvent, and 5 to 20 mg of PCBM ([6,6]-phenyl-C61-butyric acid isomethyl ester, chemical formula C 72 H 14 O2) and 5~20mg C 60 Dissolved together in a mixed solvent, and spin coated on the ITO / 4PADCB / PVSK film at a spin coating speed of 1200-1800 rpm and a spin coating time of 40-50 s, so that the electron transport layer is covered on the perovskite layer to obtain a third film, which can be named ITO / 4PADCB / PVSK / PCBM; C 60 film.

[0015] Step 6: Preferably, the electron transport layer can also be optimized: evaporate C again 60 To optimize the electron transport layer, the evaporation rate can be 0.05~0.2 Å / s, and the evaporation thickness can be 5~15nm, thereby obtaining the optimized ITO / 4PADCB / PVSK / PCBM; C 60 Thin film. Generally, a vacuum evaporator is used for evaporation.

[0016] In step S7, for example, a vacuum evaporator can be used to evaporate BCP on ITO / 4PADCB / PVSK / PCBM; C 60 On the film, the evaporation rate can be 0.05~0.2 Å / s, and the evaporation thickness can be 5~15nm, so that a buffer layer is provided on the electron transport layer to obtain a fourth film, and the fourth film can be named ITO / 4PADCB / PVSK / PCBM; C 60 / BCP film.

[0017] In step S8, the electrode may be Ag or Cu or a composite electrode of the two. Preferably, the electrode may be deposited on ITO / 4PADCB / PVSK / PCBM; 60 The surface of the / BCP film can be deposited at a rate of 0.2-1.0 Å / s and a thickness of 700 nm, so that an electrode is provided on the buffer layer, and finally a perovskite solar cell device containing the additive is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a schematic diagram of the structure of a perovskite solar cell in an embodiment of the present application; Figure 2 The SEM images, BED-C images and cross-sectional images of the perovskite films of the embodiments and comparative examples of the present application are shown; Figure 3 The AFM morphology images and phase images of the perovskite films of the embodiments and comparative examples of the present application are shown; Figure 4 GIWAXS characterization diagram of the perovskite film of the embodiment and comparative example of the present application Figure 5 is a diagram showing the surface potential distribution of perovskite films of the embodiments of the present application and the comparative examples; Figure 6 is a current distribution diagram of the perovskite film of the embodiment of the present application and the comparative example; Figure 7 It is a result diagram of in-situ UV testing of perovskite films of the embodiments and comparative examples of the present application at a variable temperature of 20-100°C; Figure 8Schematic diagram showing SED test and BED-C test of perovskite films of the embodiment of the present application and the comparative example at different annealing times; Fig. 9 The SED graph and BED-C graph of the perovskite film of the embodiment and the comparative example of the present application at different annealing times; Fig.10 The perovskite film is prepared in the embodiment of the present application 1 The result of H NMR liquid state nuclear magnetic characterization; Fig.11 This is a result diagram of XPS and FTIR testing of the perovskite film of the embodiment of the present application; Fig.12 PL test results of perovskite films of the embodiment and comparative example of the present application; Fig.13 Result diagram of TRPL test of perovskite films of the embodiment of the present application and the comparative example; Fig.14 This is a result diagram of a systematic characterization of the component distribution of the Target film using TOF-SIMS in an embodiment of the present application; Fig.15 is a schematic diagram of the additive in the perovskite film in the embodiment of the present application; Fig.16 is a result diagram of UPS test of perovskite films of the embodiment of the present application and the comparative example; Fig.17 1 is an energy level structure diagram of the perovskite film of the embodiment and the comparative example of the present application; Fig.18 It is a result diagram of XPS test characterizing the freshly prepared (Control-Fresh) and 10-day aged perovskite films of the embodiments and comparative examples of the present application; Fig.19 The results of SEM testing of the embodiments and comparative examples of the present application to characterize the perovskite films prepared freshly (Control-Fresh) and after aging for 7 days are shown; Fig. 20 Schematic diagram of the optical appearance changes of the perovskite film monitored for 10 consecutive days in the embodiments and comparative examples of the present application; Fig.21 This is a graph showing the changes in the XRD spectra of the perovskite film monitored for 10 consecutive days in the embodiments and comparative examples of the present application; Fig. 22 It is a JV curve graph and an EQE curve graph of the perovskite solar cell of the present application; Fig.23 It is a PCE performance parameter diagram of the perovskite solar cell of the embodiment of the present application and the comparative example; Fig.24This is a stability test diagram of the perovskite solar cell device of the embodiment of the present application and the comparative example under the first environmental condition; Fig.25 is a stability test diagram of the perovskite solar cell device of the embodiment of the present application and the comparative example under the second environmental condition; Fig.26 It is a dark current test diagram of the perovskite solar cell device of the embodiment of the present application and the comparative example; Fig. 27 It is a SCLC test diagram of the perovskite solar cell device of other embodiments and comparative examples of the present application. DETAILED DESCRIPTION

[0019] The following is further described by examples. It should be understood that the specific examples described herein are only used to explain the present invention, rather than to limit the present invention.

[0020] Example 1 Step 1: Use detergent, deionized water, ethanol, and isopropanol to ultrasonically clean the ITO conductive glass substrate once, each time for 15 minutes, and then treat the ITO glass substrate after ultrasonic cleaning with an ozone-UV surface cleaner for 15 minutes.

[0021] Step 2: Transfer the ITO conductive glass substrate to a glove box filled with nitrogen, and then spin-coat 0.5 mg / ml 4PADCB solution (solvent: CH3OH) on the conductive substrate at a spin-coating speed of 4000 rpm and a spin-coating time of 40 s, and anneal at 100°C for 10 min to obtain an ITO / 4PADCB film. Then, the ITO / 4PADCB film is cleaned. Specifically, the IPA solvent is spin-coated on the ITO / 4PADCB film at a spin-coating speed of 5000 rpm and a spin-coating time of 30 s, and annealed at 100°C for 5 min to obtain a cleaned ITO / 4PADCB film.

[0022] Step 3: Weigh 15 mg MACl, 21.24 mg CsI, 13.27 mg MAI, 4.25 mg MABr, 241.1 mg FAI, 14.02 mg PbBr2, and 787.77 mg PbI2, and dissolve them in a mixed solvent of DMF and DMSO, wherein 800 uL DMF and 200 uL DMSO are mixed.

[0023] Step 4: Add 0.3 mg of methyl hydrazinothiohydrazine hydroiodide solid to 1 ml of the prepared first precursor solution, and stir with a magnetic stirrer for 1 hour to obtain a second precursor solution.

[0024] Step 5: Spin the second precursor solution onto the ITO / 4PADCB film twice, wherein the first spin coating speed is 1000 rpm and the spin coating time is 10 s; the second spin coating speed is 3500 rpm and the spin coating time is 35 s. In addition, 15 seconds before the end of the spin coating process, 150 μL of CB anti-solvent is added, and then annealed at 100°C for about 30 minutes to obtain an ITO / 4PADCB / PVSK film, i.e., a perovskite film.

[0025] Step 6: Mix 500uL CB solvent and 500uL IPA solvent to form a mixed solvent, and add 10mg PCBM and 10mg C 60 The 200 nanometers were dissolved in a mixed solvent and spin-coated on the ITO / 4PADCB / PVSK film at a spin-coating speed of 1500 rpm and a spin-coating time of 45 s, so that the electron transport layer was covered on the perovskite layer to obtain ITO / 4PADCB / PVSK / PCBM / C. 60 Then, a vacuum evaporator was used to deposit C 60 Optimize the electron transport layer, the evaporation speed can be 0.1Å / s, and the evaporation thickness can be 10nm, so that the optimized ITO / 4PADCB / PVSK / PCBM is presented; C 60 film.

[0026] Step 7: Use a vacuum evaporator to evaporate BCP at a rate of 0.1 Å / s and a thickness of 10 nm, covering ITO / 4PADCB / PVSK / PCBM; C 60 The film is provided with a buffer layer on the electron transport layer to obtain ITO / 4PADCB / PVSK / PCBM; C 60 / BCP film.

[0027] Step 8: Vacuum evaporation can be used for evaporation, where the evaporation rate can be 0.2-1.0 Å / s, the evaporation thickness can be 700nm, covering ITO / 4PADCB / PVSK / PCBM; C 60 / BCP film surface, so that an electrode is provided on the buffer layer to obtain a complete perovskite solar cell device, i.e., ITO / 4PADCB / PVSK / PCBM; C 60 / BCP / Ag device, structure such as Figure 1 shown.

[0028] The present invention also provides a comparative example 1, which does not include step 4 in embodiment 1, that is, comparative example 1 only includes steps 1, 2, 3, 4, 5, 6, and 7. In addition, step 4 of comparative example 1 is to replace the second precursor solution of step 5 in embodiment 1 with the first precursor solution; the remaining steps are adaptively adjusted and are not described here. In addition, in order to distinguish the perovskite film (additives are introduced) under the embodiment and the comparative example, the perovskite film under the embodiment is named Target film, and the perovskite film of the perovskite film (additives are not introduced) under the comparative example is named Control film. At the same time, in order to distinguish the perovskite solar cell device under the embodiment and the comparative example, the perovskite solar cell device under the embodiment is named Target device, and the perovskite solar cell device under the comparative example is named Control device.

[0029] First, the present invention tests and explores the morphology and crystallization kinetics of perovskite films (Target film and Control film), as follows.

[0030] like Figure 2 As shown in Figure a, in the SEM-SED mode, the grain size of the Control film is small, the grain boundaries are densely distributed and uneven, and the surface morphology shows many grain boundary defects, indicating that its crystallization quality is low. The grain size of the Target film is significantly increased, the grain boundaries are reduced and arranged more regularly, and the grain boundary defects are significantly reduced, indicating that the introduction of additives can effectively regulate the crystallization process of perovskite, promote the orderly growth of crystals, and significantly improve the morphology and crystal quality of the perovskite film.

[0031] In order to further explore the role of additives in crystallization regulation, the present invention also uses BED-C to characterize the composition distribution of the target film and the control film. The signal intensity of the backscattered electron is closely related to the atomic number of the sample. The higher the atomic number, the stronger the signal and the brighter the generated grayscale image. Therefore, the BED-C mode can reflect the composition comparison information and distribution characteristics of the sample. Figure 2 As shown in b, the residual PbI2 in the Control film appears as large-sized lead iodide clusters, which are randomly distributed in the bulk phase of the perovskite and lack a clear distribution pattern with the crystal. The random distribution of PbI2 easily leads to inhomogeneity within the crystal, increasing grain boundary defects and the probability of carrier recombination. In the Target film modified with additives, the residual PbI2 shows a tendency to migrate from the bulk phase to the grain boundary, and forms a uniformly distributed enriched area at the grain boundary. This shows that the additive successfully regulates the migration path and enrichment behavior of PbI2 during the crystallization process, passivates grain boundary defects, and enhances the stability of the grain boundary.

[0032] Furthermore, in the cross-sectional test of the perovskite film, e.g. Figure 2As shown in Figure c, it is observed that the grains inside the Control film are smaller, and there is a clear discontinuity between the grain boundaries, and the density of the Control film is poor. However, the grains in the cross section of the Target film are significantly larger, and the connection between the grains is tighter, and the Target film is denser and smoother, further proving that the crystallization regulation of the additive significantly improves the microstructure of the perovskite film.

[0033] Furthermore, if Figure 3 As shown in a, the AFM morphology image shows significant differences in the surface morphology of the Target film and the Control film. The Control film shows a more obvious small and unevenly distributed grain structure, with large gaps between its grains; while in the Target film, the grain size is significantly increased and the grain distribution is more uniform, which again shows that the additive promotes the orderly growth of crystals, thereby improving the overall quality of the film. In addition, Figure 3 The results of the phase diagram further support the above conclusions, as shown in Figure 2b, where the Control film shows an uneven phase distribution, indicating random grain orientation and high defect density. In the Target film, the phase distribution is more uniform, indicating that the crystal quality of the crystal is significantly improved.

[0034] Furthermore, in order to further evaluate the crystallinity of the film, the present invention also performed GIWAXS characterization on the target film and the control film. The diffraction pattern clearly shows the effect of the additive on the crystal structure of the perovskite film. Figure 4 As shown in the figure, in the Control film, the diffraction rings of the (001), (011) and (002) crystal planes are more diffusely distributed and the signals are weaker, indicating that the perovskite film has low crystallinity and disordered grain arrangement. At the same time, the wider diffraction rings show that there are more defects and inhomogeneities in the internal structure of the crystal, which is consistent with the AFM results. In contrast, the Target film shows clearer and stronger diffraction rings, especially the diffraction peak intensity on the (001), (011), (111) and (002) crystal planes is enhanced. This shows that the additive effectively promotes the orderly growth of the crystals and improves the orientation and crystallinity of the crystals. The stronger diffraction signals and more concentrated diffraction rings indicate that the grain arrangement of the Target film is more orderly and the crystallization quality is significantly better than that of the Control film.

[0035] Furthermore, in order to study the effects of crystallization-retarding additives on the surface potential distribution and carrier transport properties of perovskite films, the present invention characterized the Control film and the Target film using open circuit voltage scanning potential microscopy (KPFM) and conductive atomic force microscopy (c-AFM). Figure 5The surface potential distribution of the Control film and the Target film. The potential distribution of the Control film shows a large inhomogeneity, and the potential value range is concentrated around 350mV, indicating that there are significant potential fluctuations inside the perovskite film, which may be caused by the inhomogeneity between grains and the carrier aggregation caused by more grain boundary defects. In contrast, the Target film shows a more uniform potential distribution, and the potential fluctuation is significantly reduced. This shows that the additive regulates grain growth by delaying crystallization, effectively reducing grain boundary defects and local electric field distortion at the grain boundary, thereby optimizing the potential uniformity of the perovskite film.

[0036] Furthermore, the present invention also measures the current distribution of the control film and the target film by conductive atomic force microscopy at a voltage of 1.5 V. Figure 6 As shown in the figure, the local current distribution at the grain boundaries of the Control film shows a high degree of inhomogeneity, indicating that the charge migration behavior at the grain boundaries inside the perovskite film is quite different from that in the bulk phase, which reduces the charge transfer efficiency. In contrast, the Target film shows a more uniform current distribution, and most of the grain boundaries are not much different from the bulk phase. It can be seen that after the additive regulates the crystallization process, the grain size increases significantly, the number of grain boundaries decreases, and the defects at the grain boundaries are partially passivated, thereby improving the carrier transport capacity and uniformity of the perovskite film.

[0037] Furthermore, the present invention also conducted in-situ UV tests on the control film and the target film at a variable temperature of 20-100°C and SED tests and BED-C tests at a constant temperature of 100°C for different time periods to further study the growth of perovskite crystals. Figure 7 As shown in the in-situ UV test at a variable temperature of 20~100℃, the Target film changed the crystal dynamics of the perovskite precursor solution due to the introduction of the additive. The additive and Pb in the perovskite precursor solution 2+ or I - The interaction between the two promotes the rapid nucleation of perovskite, allowing the crystal to nucleate rapidly in the early stages. The crystal nucleation is faster, and the perovskite absorption peak appears in a shorter time. In addition, the introduction of additives regulates the growth process of perovskite crystals, making the crystal growth more orderly and slow, avoiding the formation of large particles, and controlling the relatively slow growth rate of the Target film crystals, making it take longer to reach the highest point of crystal maturation. After the crystal maturation is completed, the ultraviolet absorption intensity is stronger, indicating that the crystal quality is higher, the degree of disorder is lower, and higher quality thin film crystals are obtained. Therefore, due to the improvement of crystal quality and the increase of crystallinity, the Target film achieves better film uniformity, fewer grain boundary defects and better PbI2 distribution, and the ultraviolet absorption intensity is greatly improved.

[0038] Further, the present invention also provides Example 2, Example 3 and Example 4, wherein, compared with Example 1, Examples 2, 3 and 4 are the same except that the annealing time in step 5 is changed to 5s, 5min and 20min, and the other steps are unchanged. Adaptively, Comparative Examples 2, 3 and 4 are provided, and the annealing time in Comparative Examples 2, 3 and 4 is changed to 5s, 5min and 20min, and the other steps are unchanged. Figure 8 As shown, the Target films obtained in Examples 2, 3 and 4, and the Control films obtained in Comparative Examples 2, 3 and 4 were subjected to SED tests and BED-C tests. Fig. 9 As shown in the figure, in the SED test and BED-C test of the perovskite film at different annealing times, as the annealing time increases, the initial grains of the Control film are quite different, and heterogeneous crystallization occurs. In addition, due to the excessively fast growth rate, the growth difference between the grains is increased. In the subsequent cracking process, the voids cannot be completely eliminated, forming a PbI2 coating, and the perovskite crystal undergoes unstable recrystallization or decrystallization. At the same time, the appearance of black holes in the Control film in the BED-C mode indicates that voids or defective areas are formed during the annealing process. These areas may be caused by excessive deposition of PbI2 inside the crystal or the aggregation of defects. The formation of holes will affect the photoelectric conversion efficiency and long-term stability of the perovskite film. In the SED mode, the perovskite unit cell size of the Target film remains relatively stable as the annealing time increases. This phenomenon shows that the additive effectively regulates the growth process of the crystal, avoids excessive or uneven crystallization, and prevents the collapse or shrinkage of the crystal. In the BED-C mode, the Target film greatly reduced the appearance of black holes in the Control group. The passivation effect of the additive effectively prevented the formation of defects and maintained good stability during the annealing process, so that there were no obvious voids or defective areas in the crystal. Compared with the Control film, the PbI2 in the Target film migrated from the inside of the perovskite unit cell to the grain boundary for enrichment. The additive effectively regulated the precipitation distribution position of PbI2 in the perovskite crystal, enriching it at the grain boundary, thereby playing a role in passivating the grain boundary defects.

[0039] Furthermore, in order to explain the changes in the crystallization process, the present invention has proved through various characterizations that the additives have a strong interaction with the perovskite components. The additives can combine with the perovskite components to form an intermediate phase, slowing down the growth of the perovskite film crystals, thereby leading to different crystallization processes. The specific tests are as follows.

[0040] The present invention is carried out by mixing equimolar additives and FAI into DMSO- d 6 Experiment 1 of the reaction in solution, and mixing the additive and PbI2 in equal molar ratio into DMSO- d6 Experiment 2 of the reaction in solution. 1 H NMR liquid nuclear magnetic resonance characterization was used to study the effect of additives. Fig.10 a and 10b, the ─NH, ─NH2 and ─CH3 groups in the additive 1 The H signals are located at 9.68, 5.33-5.16 and 2.38 ppm, respectively, with an integration ratio of 1:4:3. 1 The H signals were located at 8.82 and 7.85 ppm, respectively, with an integration ratio of 4:1. 1 The H signals changed to 9.01, 8.68-8.64 and 7.91-7.80 ppm respectively. After the second experiment, the ─NH2, ─NH and ─CH3 groups in the additive 1 The H signals shifted to 9.65, 5.33-5.20, and 2.38 ppm, respectively. 1 H NMR liquid state nuclear magnetic resonance characterization data prove that the additives can form a new interaction with FAI and PbI2.

[0041] In addition, if Fig.11 The present invention uses XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared spectroscopy) to test the chemical composition and bonding changes of additives. Fig.11 As shown in a, in the XPS test of the Target film, Pb 4f The Pb 2+ The chemical environment of the 3d They move from 618.84 eV and 630.28 eV to 619.03 eV and 630.51 eV respectively. 1s Moving from 400.21 eV to 400.34 eV, I 3d and N 1s The shift of the XPS peaks toward higher binding energies reflects the decrease in charge density on these atoms and is attributed to the interaction between the additive and the perovskite. Fig.11 As shown in b, in the FTIR test, the frequency change of NH stretching vibration indicates that the hydrogen bonding environment on N has changed, N is involved in a stronger hydrogen bond, or its coordination environment has changed, and the C=N bond has also undergone electron redistribution or electrical changes in adjacent groups, which corresponds to the liquid NMR test results.

[0042] Furthermore, in the PL test, if Fig.12As shown in the figure, the intensity of the Target film is significantly enhanced compared to the Control film, indicating that the additive effectively passivates the defects in the perovskite film, reduces the non-radiative recombination process, and improves the efficiency of radiative recombination. Therefore, more electron-hole pairs release energy through luminescence, resulting in an increase in PL intensity. Enhanced luminescence intensity usually indicates an increase in the probability of radiative recombination in the material and a decrease in non-radiative recombination pathways.

[0043] Furthermore, the present invention performs TRPL testing to study the recombination dynamics of carriers. The TRPL decay curve can be described by two time constants (τ1 and τ2), τ1 corresponds to a fast recombination process, and τ2 corresponds to a slower recombination process, which is usually related to carrier recombination in bulk materials, especially to bulk radiation recombination paths. Fig.13 As shown, τ1 in the Target film becomes smaller while τ2 increases, indicating that with the introduction of additives, the bulk defect states of the perovskite film are effectively passivated, non-radiative recombination is reduced, resulting in carriers being able to remain in the material for a longer time, ultimately improving the overall performance of the perovskite solar cell device.

[0044] Secondly, in order to further study the distribution of additives in perovskite films and their regulatory effects on the distribution of PbI2, the present invention uses time-of-flight secondary ion mass spectrometry (TOF-SIMS) technology to systematically characterize the component distribution of the Target film. Fig.14 As shown, the additives are distributed throughout the perovskite system, but the distribution intensity has a certain gradient characteristic.

[0045] Specifically, the additives are relatively more distributed in the upper and lower interface regions of the perovskite film (e.g. Fig.15 The signal intensity of the additive near the electron transport layer of the perovskite film is higher, indicating that the additive is partially enriched on the upper surface of the perovskite film. The additive enriched on the upper interface passivates the non-radiative recombination defects on the upper surface, such as I - Vacant or unsaturated FA + , improving the interface quality and carrier transport efficiency. The signal intensity of the additive is highest at the bottom of the perovskite film near the hole transport layer, and the additive enrichment at the lower interface is significantly higher than that at the upper interface. The distribution characteristics of the additive indicate that the additive is preferentially enriched in the contact area between the perovskite and the hole transport layer during the crystallization process. This may be attributed to the dynamic chemical reaction in the precursor solution during the crystal growth process. The additive is enriched by the FA + or I -The formation of coordination bonds delays the rapid nucleation of the lower interface nucleus and promotes the orderly crystal growth. The gradient distribution of the additive at the upper and lower interfaces significantly improves the defect passivation ability of the additive at the upper and lower interfaces of the perovskite film. Under the action of the additive, the distribution of PbI2 in the Target film has achieved significant stability and uniformity. The PbI2 signal intensity is evenly distributed throughout the bulk of the perovskite film, avoiding the aggregation of PbI2 clusters in the bulk phase, and there is no obvious local concentration difference. The distribution of PbI2 shows that the additive delays the crystallization rate and regulates the crystallization kinetics, so that PbI2 can be dispersed in a more uniform manner throughout the perovskite film during the growth of the perovskite film.

[0046] In order to further study the regulatory effect of additives on the energy level structure of perovskite films, ultraviolet photoelectron spectroscopy (UPS) was used to characterize the work function (WF), the highest energy level of the valence band (EVBM), and the lowest energy level of the conduction band (ECBM) of the control film and the target film. Fig.16 Combining UPS data and band gap (Eg = 1.56 eV) information, the energy level structure diagram of the Control film and the Target film was constructed, as shown in Fig.17 As shown, the effect of crystallization regulation on the energy level distribution of the film is revealed. Specifically, the WF = 5.12 eV of the Target film is higher than that of the Control film WF = 4.94 eV. Compared with the Control film, the VBM and CBM of the Target film shifted from 5.99 eV and 4.43 eV to 5.91 eV and 4.35 eV, respectively, indicating that the additive optimizes the energy band arrangement and reduces the possibility of carrier recombination, thereby improving the photoelectric performance of the perovskite film.

[0047] Furthermore, in order to study the effect of additives on the stability of perovskite films, the present invention firstly uses X-ray photoelectron spectroscopy (XPS) to characterize the chemical shift changes of Pb, I and N in the Control film prepared freshly (Control-Fresh) and after aging for 10 days (Control-10 Days), as well as the chemical shift changes of Pb, I and N in the Target film prepared freshly (Target-Fresh) and after aging for 10 days (Target-10 Days). Combined with the XPS data, the chemical environment changes of the elements in the Control film and the Target film are compared to explore the mechanism of action of additives in improving the stability of perovskite films. Fig.18 As shown in the figure, after aging for 10 days, the Pb 4fThe peak position of the binding energy obviously shifted toward the high binding energy direction, with a shift of about +0.3 eV compared to the freshly prepared Control film, indicating that the Control film was exposed to oxygen and moisture in the environment, resulting in chemical degradation. 4f The binding energy shifted slightly to +0.1 eV, indicating that Pb 2+ The chemical environment is more stable. Due to the passivation effect of the additives at the grain boundaries and interfaces, the intrusion of external moisture and oxygen is prevented, and the degradation phenomenon is significantly suppressed. Fig.18 As shown, after aging, the control film 3d The peak position shifted significantly to +0.9 eV, indicating that I - The chemical environment of the - When exposed to the external environment, it reacts with moisture or oxygen to form chemical byproducts (such as HI or I2), causing the control film to degrade and causing I - The binding energy increases. After aging, the Target film, I 3d The positive shift amplitude of the peak position was significantly reduced, indicating that the additive had an - The chemical environment of the additive plays a stabilizing role. The interface passivation and crystallization regulation of the additive form a protective barrier at the grain boundary, inhibiting the I - Direct contact with the external environment, thus reducing the possibility of chemical reactions. 1s The signal mainly comes from FA + Cations, whose chemical shifts can reflect the degradation of organic components. Fig.18 As shown, after aging, the control film has 1s The binding energy shows a significant positive shift of about +0.6 eV, indicating that FA + The cations are partially degraded under the action of moisture. 1s The peak position changes very little, about +0.2 eV, indicating that the additive effectively passivates the grain boundary defects in the delayed crystallization process, reduces the degradation rate of organic components, and the passivation effect further enhances the chemical stability of the film.

[0048] Furthermore, the present invention uses scanning electron microscopy (SEM) to characterize the freshly prepared (Fresh) and aged for 7 days (7Days) Control film, and the freshly prepared (Fresh) and aged for 7 days (7 Days) Target film, and uses SED mode (surface morphology) and BED-C mode (composition distribution) to analyze the morphological changes and PbI2 enrichment behavior of the film. Fig.19As shown in the figure, the surface morphology of the aged Control film is significantly degraded in the SED mode (Control-SED-7 Days), the grain structure becomes irregular, and many holes appear at the grain boundaries, indicating that the film has been severely degraded under the action of environmental humidity and oxygen. In the BED-C mode (Control-BED-C-7 Days), the bulk clustering phenomenon of PbI2 is further aggravated, and a large number of PbI2 clusters are concentrated inside the unit cell. The uneven distribution of PbI2 leads to an increase in the number of grain boundary defects, which significantly reduces the stability of the film. In the SED mode (Target-SED-7 Days), the grain structure of the aged Target film remains basically intact, the grain boundaries are still regular, and only slight degradation occurs on the surface. This shows that the additive significantly improves the stability of the film in moisture and oxygen environments. In the BED-C mode (Target-BED-C-7 Days), the enrichment of PbI2 distribution grain boundary clusters is significantly reduced compared with the Control film. This further indicates that the additive forms a protective barrier by interfacial passivation and optimizing PbI2 distribution, preventing moisture and oxygen from attacking the grain boundaries and significantly inhibiting the structural degradation of the film during aging.

[0049] Furthermore, the present invention continuously monitors the optical appearance changes and X-ray diffraction (XRD) spectra of the Control film and the Target film for 10 days to compare and analyze the stability of the Control film and the Target film in a humid environment. Combined with the film morphology and crystal structure evolution trend, the inhibitory effect of the crystallization control strategy on film degradation is further explored. Fig. 20 As shown, the color of the Control film gradually faded with the increase of aging time, from the original black to light yellow. On the 8th day, obvious yellow areas appeared in the film, indicating that the perovskite had undergone significant degradation and formed a perovskite yellow phase. By the 10th day, the Control film almost completely turned yellow, indicating that the perovskite layer had lost its structural integrity in a humid environment. During the same aging time, the color of the Target film remained stable. Even on the 10th day, the film remained black, and no obvious yellow phase was generated. The stability of the optical appearance shows that the additive significantly improved the film's anti-degradation ability through crystallization regulation, effectively delaying the aging process of the perovskite layer. As shown Fig.21As shown, the XRD spectrum shows that as the aging time of the Control film increases, the characteristic peak of the perovskite at 14.1°, corresponding to the 001 crystal plane, gradually weakens, indicating that the perovskite crystal structure has degraded. At the same time, the characteristic diffraction peak of PbI2 at 12.6° increases significantly with time. This shows that the decomposition of perovskite into PbI2 in the Control film is the main pathway of its degradation. In contrast, the characteristic peak of the perovskite of the Target film remains stable in intensity after 10 days of aging, and no obvious attenuation is observed. This shows that the passivation effect of the additive in the film effectively inhibits the decomposition of the perovskite crystal.

[0050] Finally, the present invention performs performance tests on the obtained Target device and Control device. Under the simulated AM 1.5G solar radiation intensity, Fig. 22 As shown in a, the energy conversion efficiency (PCE) of the Target device reaches a maximum of 25.05%, and the open circuit voltage (V OC ) reaches a maximum of 1.159V, the fill factor (FF) reaches a maximum of 83.13%, and the short-circuit current density (J SC ) up to 25.99 mA cm -2 , while the PCE of the Control device reaches a maximum of 22.93%, V OC The maximum value reaches 1.141V, the maximum FF reaches 78.88%, and the J SC The maximum value reaches 25.47mA cm -2 In comparison, the performance of Target devices is significantly enhanced. Fig. 22 As shown in b, the JSC calculated from the external quantum efficiency (EQE) curves of the Control device and the Target device are 24.19 mA cm -2 and 24.26 mA cm -2 In addition, the present invention also analyzes the performance parameters of 20 Target devices prepared by Example 1 and 20 Control devices prepared by Comparative Example 1, such as Fig.23 As shown in the figure, after being modified by additives, the average PCE of the perovskite solar cell device increased from 22.28% to 24.61%. It can be seen that it is precisely because of the regulation of the crystallization rate of the perovskite film by the additives that the crystal growth process is optimized, the crystal defect density is reduced, and the quality of the perovskite film is significantly improved, thereby significantly improving the performance parameters of the perovskite solar cell device and enhancing the photoelectric conversion performance of the perovskite solar cell device.

[0051] Furthermore, the present invention conducted a stability test on a perovskite solar cell device under conditions of simulated continuous sunlight radiation. Fig.24As shown, the stable power output (SPO) of the device was measured by an IT monitor at the maximum power point (Mapping). During the 300-second illumination period, the Target device maintained a stable PCE at 23.71%, while the PCE of the Control device continued to drop to 20.91%. Due to the synergistic effects of the hydrophobicity of the additive, defect passivation, and directional enrichment at the PbI2 grain boundaries, the long-term stability of the Target device is significantly improved compared to the Control device. Fig.25 As shown in the figure, the unpackaged Target device still maintains 93% of its initial PCE after 1000 hours in a dark, 25°C, and 30% to 40% relative humidity environment. In contrast, under the same conditions, the PCE of the Control device drops to 75%, which shows that the stability of the Target device is much higher than that of the Control device.

[0052] Furthermore, the present invention also uses dark current (Dark JV) to test the effect of additives on perovskite solar cell devices, such as Fig.26 As shown, the dark current of the Target device is significantly lower than that of the Control device, indicating that the impact of leakage current can be reduced.

[0053] Furthermore, the present invention prepares two hole devices with and without additives introduced into the perovskite layer, namely, ITO / 4PADCB / PVSK / PSS:PEDOT / Ag device, which is also a perovskite solar cell device, mainly used for space-confined charge current (SCLC) test. Compared with ITO / 4PADCB / PVSK / PCBM;C60 / BCP / Ag device, there are differences in the preparation of buffer layer and electron transport layer, but it is well known in the art and will not be elaborated here. Fig. 27 As shown, the TFL cutoff potential is advanced from 1.07 V to 0.89 V. The results also confirm that the internal defects are filled due to the introduction of additives and the directional enrichment of PbI2 at the grain boundaries.

[0054] Further, in order to explore the effect of the content of methyl hydrazinothiohydrazinecarboxylate hydroiodide in step 4 on the cell efficiency of the perovskite solar cell device, the present invention provides Examples 5 and 6. Compared with Example 1, except that the additive content in step 4 is changed to 0.1 mg and 0.5 mg, the remaining steps remain unchanged. It can be understood that the additive content in Comparative Example 1 is changed to 0 mg. The cell efficiency of the perovskite solar cell devices of Example 1, Example 5, Example 6 and Comparative Example 1 is measured. As shown in the following table, the cell efficiency of the perovskite solar cell introduced with the additive can be improved, and when the additive content is 0.3 mg, the cell efficiency is the highest.

[0055]

[0056] Further, in order to explore the effect of the second spin coating speed in step 5 on the cell efficiency of the perovskite solar cell device, the present invention provides Examples 7 and 8. Compared with Example 1, except that the second spin coating speed in step 5 is changed to 3000rpm and 4000rpm, the other steps remain unchanged. Adaptively, Comparative Examples 5 and 6 are also provided. Compared with Comparative Example 1, except that the second spin coating speed in step 5 is changed to 3000rpm and 4000rpm, the other steps remain unchanged. The cell efficiency of the perovskite solar cell devices of Example 1, Example 7, Example 8 and Comparative Example 1, Comparative Example 5 and Comparative Example 6 is measured. As shown in the following table, the cell efficiency of the perovskite solar cell introduced with the additive can be improved, and the cell efficiency is the highest when the second spin coating speed is 3500rpm.

[0057]

[0058] Further, in order to explore the effect of the annealing time in step 5 on the cell efficiency of the perovskite solar cell device, the present invention provides Examples 9 and 10. Compared with Example 1, except that the annealing time in step 5 is changed to 20min and 40min, the other steps remain unchanged. Adaptively, Comparative Examples 7 and 8 are also provided. Compared with Comparative Example 1, except that the annealing time in step 5 is changed to 20min and 40min, the other steps remain unchanged. The cell efficiency of the perovskite solar cell devices of Example 1, Example 9, Example 10 and Comparative Example 1, Comparative Example 7 and Comparative Example 8 is measured. As shown in Table 3, the cell efficiency of the perovskite solar cell introduced with the additive can be improved, and the cell efficiency is the highest when the annealing time in step 5 is 30min.

[0059]

[0060] The above is a description of the technical solution provided by the present invention. For those skilled in the art, according to the ideas of the embodiments of the present invention, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A perovskite solar cell, characterized in that: The method comprises a conductive substrate layer, a hole transport layer, a perovskite layer, an electron transport layer, a buffer layer and an electrode in the direction of the evaporation thickness. The perovskite layer contains methyl hydrazinethiohydrazone formate hydroiodide for modifying the perovskite. The structural formula of methyl hydrazinethiohydrazone formate hydroiodide is The general structural formula of the perovskite is ABX3, wherein A is a metal cation and / or an alkylammonium salt, B is a divalent metal cation, and C is a halogen anion; and A includes NH2CHNH2 + , the B includes Pb 2+ , the C includes I - , so that the perovskite contains components FAI and PbI2.

2. The perovskite solar cell according to claim 1, characterized in that The A also includes Cs + , K + , Rb + and / or CH3NH3 + , the B also includes Cu 2+ 、Ni 2+ 、Co 2+ 、Cd 2+ ,Ge 2+ and / or Sn 2+ , the X also includes Br - and / or Cl - .

3. A method for preparing a perovskite solar cell as claimed in claim 1 or 2, characterized in that: The preparation method comprises: Step S1: Cleaning cleaning the conductive substrate to obtain a conductive base layer; Step S2: preparing a hole transport layer Using 4PADCB solution to spin-coat and anneal the cleaned conductive substrate to obtain a first thin film; Step S3: preparing a first precursor solution Dissolving solid AX and solid BX2 in a mixed solvent of DMF and DMSO to prepare a first precursor solution; wherein AX includes FAI and BX2 includes PbI2; Step S4: preparing a second precursor solution Adding an additive, methyl hydrazinothiohydrazine hydroiodide solid, to the prepared first precursor solution, stirring to allow a full reaction, to obtain a second precursor solution; Step S5: preparing a perovskite layer Spin coating the second precursor solution on the first film, and before the spin coating process is completed, dropwise add CB anti-solvent, and then anneal to obtain a second film; Step S6: preparing an electron transport layer PCBM and C 60 Dissolved in a mixed solvent of CB and IPA, and spin-coated on the second film, and then evaporated C 60 , obtaining a third film; Step S7: preparing a buffer layer Vapor-depositing BCP on the third film to obtain a fourth film; Step S8: preparing electrodes An electrode is evaporated on the fourth film to finally obtain a perovskite solar cell device containing methyl hydrazinothiohydrazinecarboxylate hydroiodide as an additive.

4. The preparation method according to claim 3, characterized in that: In step S4, the first precursor solution is Xml, and the solid of methyl hydrazinothiohydrazine hydroiodide is Ymg, wherein X:Y is 10:(1-5).

5. The preparation method according to claim 3, characterized in that: In step S5, the annealing temperature is 100° C. and the annealing time is 20 to 40 minutes.

6. The preparation method according to claim 3, characterized in that: In step S5, two different spin coating speeds are used for spin coating, wherein the first spin coating speed is 1000 rpm, and the spin coating time is 10 s; the second spin coating speed is 3000-4000 rpm, and the spin coating time is 35 s.

7. The preparation method according to claim 3, characterized in that: In step S3, the molar ratio of AX solid to BX2 solid is 1:(1-1.4).

8. The preparation method according to claim 3, characterized in that: In step S2, the volume fraction ratio of DMF is X, and the volume fraction ratio of DMSO is Y, wherein X is 75% to 100%, and Y=1-X.

9. The preparation method according to claim 3, characterized in that: The evaporation rate in step S8 is 0.2-1.0 Å / s.

10. The preparation method according to claim 3, characterized in that: Step S3 specifically includes: Weigh 15 mg MACl, 21.24 mg CsI, 13.27 mg MAI, 4.25 mg MABr, 241.1 mg FAI, 14.02 mg PbBr2, and 787.77 mg PbI2, and dissolve them in a mixed solvent of DMF and DMSO, wherein the volume fraction ratio of DMF to DMSO is 4:1.

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