Fluoropolymer-regulated mixed halide perovskite thin films, methods of making and applications thereof

Abstract

The present application relates to the technical field of mixed halide perovskite thin film, and particularly relates to a fluorine-containing polymer regulated mixed halide perovskite thin film, a preparation method and application thereof, which comprises the following steps: perovskite precursors are weighed according to a proportioning ratio, the perovskite precursors are dissolved in a first solvent to form a mixed solvent, amino acid ligands are added to form a perovskite precursor solution; fluorine-containing polymers of a first mass concentration are added to obtain a fluorine-containing polymer perovskite precursor solution; film forming treatment is performed on a substrate to form a liquid film, and then time-sharing annealing treatment is performed so that the liquid film is initiated by the fluorine-containing polymers to form a micron-level phase separation region, liquid-liquid separation occurs, and after cooling, a fluorine-containing polymer regulated mixed halide perovskite thin film is obtained. The fluorine-containing polymers initiate the liquid-liquid phase separation process in the perovskite thin film in situ, so that the halide ions are uniformly distributed in the thin film, the lattice stress in the perovskite crystallization process is reduced, and the quality of the mixed halide perovskite thin film is improved.

Description

Technical Field

[0001] This invention relates to the field of mixed halide perovskite thin film technology, and in particular to a mixed halide perovskite thin film controlled by a fluoropolymer, its preparation method and application. Background Technology

[0002] Solution-processable metal halide perovskite films are ideal light-emitting layer materials for fabricating next-generation high-efficiency and stable light-emitting diodes (PeLEDs) due to their advantages such as high color purity, wide color gamut, and low cost. In the three-dimensional perovskite ABX3 structure of metal halide, Cs occupies the A site. + HC(NH2)2 + (FA) + ) and CH3NH3 + (MA) + ), etc. The B-site ion is generally a divalent lead metal ion. The X-site is generally composed of a halogen (Cl...). - , and (etc.) occupy. By adjusting the types of mixed halogens, the spectrum from blue light to near-infrared light can be regulated, and the spectrum based on mixed halogen perovskites has a narrow half-width and high emission color purity.

[0003] However, in the solution-based preparation of halide perovskite materials, the perovskite crystallizes too rapidly from the precursor solution, and the crystallization process is difficult to control. This results in numerous defects within the solution-prepared perovskite. Particularly for mixed halide perovskite materials, the different halide ion compositions lead to significant lattice stress during crystallization. This results in numerous Ruddlesden-Popper (RP) type high-dimensional surface defects within the mixed halide perovskite. The presence of these surface defects leads to band edge defects in the perovskite, thereby affecting its luminescent properties. Summary of the Invention

[0004] To address at least one of the aforementioned technical problems, this invention proposes a fluoropolymer-controlled mixed halide perovskite thin film and its preparation method. By introducing fluoropolymers of different molecular weights into a mixed halide perovskite precursor solution, and during low-temperature annealing, the fluoropolymers initiate an in-situ liquid-liquid phase separation process within the perovskite thin film, resulting in a uniform distribution of halide ions within the film. This reduces the lattice stress during the perovskite crystallization process, improves the quality of the mixed halide perovskite thin film, and ultimately optimizes the performance of perovskite LED devices.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] The first aspect of this invention provides a method for preparing mixed halide perovskite thin films controlled by fluoropolymers, comprising the following steps:

[0007] S1, the perovskite precursor is weighed according to the proportion, dissolved in the first solvent to form a mixed solvent, and the amino acid ligand for guiding the oriented crystallization process of perovskite is added to the mixed solvent, heated and stirred to form a uniform and clear perovskite precursor solution;

[0008] S2, a first mass concentration of fluorine-containing polymer is added to the perovskite precursor solution to obtain a fluorine-containing polymer perovskite precursor solution;

[0009] S3, the fluorine-containing polymer perovskite precursor solution is subjected to film forming treatment on the substrate to form a liquid film, and then subjected to time-sharing annealing treatment to form a micron-sized phase separation region under the initiation of the fluorine-containing polymer, so that liquid-liquid separation occurs, and after cooling, a mixed halide perovskite thin film regulated by the fluorine-containing polymer is obtained.

[0010] Preferably, the general formula of the perovskite in S1 is ABX3; wherein the A-site ion is one or more of cesium ion, formamidinium ion and methylamine ion; the B-site ion is lead ion and / or tin ion; the X-site ion is one or more of chloride ion, bromide ion and iodide ion; the amino acid ligand is one or more of glycine, serine, arginine, histidine, cysteine and methionine; and the first solvent includes one or more of N,N-dimethylformamide, dimethyl sulfoxide and N-methyl pyrrolidone.

[0011] Preferably, the molar mass ratio of the amino acid ligand to the perovskite precursor, calculated based on the molar amount of the B-site ion in the perovskite precursor, is (0.05-0.2):1.

[0012] Preferably, the fluorine-containing polymer includes one or more of poly(perfluoroalkyl ethylene), poly(vinylidene fluoride), ethylene-tetrafluoroethylene copolymer, perfluoroalkoxy resin, poly(trifluorochloroethylene), fluorine-containing polyimide, fluorine-containing polyurethane, amorphous fluoropolymer and perfluoropolyether, and the molecular weight of the fluorine-containing polymer ranges from 0.6W to 100W.

[0013] Preferably, the ratio of the fluorine-containing polymer to the perovskite precursor, calculated based on the total mass of the perovskite precursor components, is (0.02-0.06):1.

[0014] Preferably, the film forming treatment includes one or more of spin coating, blade coating and drop coating.

[0015] Preferably, the time-sharing annealing includes low-temperature annealing and high-temperature annealing, the low-temperature annealing temperature is 40-100℃, and the low-temperature annealing time is 1-20 minutes; the high-temperature annealing temperature is 100-130℃, and the high-temperature annealing time is 1-200 minutes.

[0016] The second aspect of the present application provides a thin film prepared by the method for preparing a mixed halide perovskite thin film regulated by a fluorine-containing polymer according to the first aspect.

[0017] The third aspect of the present application provides an application of the thin film according to the second aspect in a semiconductor light-emitting material or a photovoltaic device.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] In the present application, different molecular weight fluorine-containing polymers are introduced into a mixed halide perovskite precursor solution. The high electronegativity (4.0) of fluorine atoms in the fluorine-containing polymer forms strong polar sites in the polymer chain. This electrostatic anchoring effect can stabilize the perovskite crystal nucleus and inhibit the disordered growth in the initial stage of crystallization. Moreover, the fluorine-containing side chain (such as -CF3, -CF2-) endows the polymer with low surface energy characteristics, which can spontaneously migrate to the gas-liquid interface in the solution state and form a dynamic self-assembled layer. This characteristic allows the polymer to continuously regulate the surface tension of the perovskite precursor solution during the film formation process, promoting the lateral uniform growth of perovskite grains. The strong interaction between the polar C-F bond in the fluoropolymer network and the polar solvent in the perovskite precursor is conducive to the retention of the polar solvent in the intermediate phase of the perovskite in the time-sharing annealing process, allowing the uniform diffusion of ion components in the film. At the same time, the polymer matrix finally exists in the grain boundary position of the perovskite thin film, which can limit the growth of perovskite grains and improve the film-forming property of the film, ultimately obtaining a perovskite thin film with uniform perovskite grain size and no pinholes. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a flow chart of the method for preparing a mixed halide perovskite thin film regulated by a fluorine-containing polymer.

[0021] Figure 2 It is an analysis diagram of the crystallization of the perovskite thin film in the present application. Among them, Figure 2 a is a CsPbI 3-x Br x X-ray diffraction pattern of the thin film after annealing at 90℃ for 10 minutes; Figure 2 b is the X-ray diffraction pattern of the perovskite thin film after annealing at 120℃ for 5 minutes.

[0022] Figure 3 It is a liquid-liquid phase separation process characterization diagram of the mixed halide CsPbI 3-x Br x thin film in the present application. Among them, Figure 3 a, Figure 3 c, Figure 3 e, respectively, are the atomic force microscope images of the perovskite thin film added with different molecular weight PVDF after annealing at 90℃ for 5 minutes. Figure 3 b,Figure 3 d, Figure 3 fAtomic force microscopy images of perovskite films with different molecular weight PVDF after annealing at 90℃ for 10 minutes, respectively.

[0023] Figure 4 CsPbI 3-x Br x Film phase and morphology analysis. Among them, Figure 4 aCsPbI 3-x Br x X-ray diffraction pattern of the film after annealing at 90℃ for 10 minutes. Figure 4 bX-ray diffraction pattern of perovskite film without adding PVDF after annealing at 120℃ for 5 minutes. Figure 4 c- Figure 4 eAtomic force microscopy images of perovskite films without adding PVDF after annealing at 90℃ for 2 minutes, 90℃ for 5 minutes and 90℃ for 10 minutes, respectively.

[0024] Figure 5 Atomic force microscopy images and particle size statistics of mixed halogen CsPbI 3-x Br x in the present application with different molecular weight PVDF. Among them, Figure 5 aAtomic force microscopy image of perovskite film with 40W PVDF added; Figure 5 bParticle size statistics of perovskite film with 40W PVDF added; Figure 5 cAtomic force microscopy of perovskite film with 53W PVDF added; Figure 5 dParticle size statistics of perovskite film with 53W PVDF added.

[0025] Figure 6 LED device performance chart of mixed halogen CsPbI 3-x Br x in the present application with different molecular weight PVDF. Among them, Figure 6 aCurrent density-voltage curve of LED device. Figure 6 bPerformance curve of luminance-voltage of LED device. Figure 6 cExternal quantum efficiency-voltage curve of LED device.

[0026] Figure 7 CsPbI 3-x Br x Film phase and morphology analysis. Among them, Figure 7 aCsPbI 3-x Br xX-ray diffraction patterns of the thin films after annealing. Figure 7 b and Figure 7 c are atomic force micrographs of the perovskite thin film with only PVDF added after annealing for 5 minutes and 10 minutes at 90 °C. Figure 7 d is a transmission electron micrograph of the perovskite thin film with only PVDF added. Figure 7 e and Figure 7 f is a characterization of the internal lattice plane defects of the perovskite thin film with only PVDF added.

[0027] Figure 8 CsPblBr with amino acid and PVDF additives without temporal annealing 3-x Br x Thin film phase and morphology analysis. Figure 8 a is CsPblBr without temporal annealing 3-x Br x X-ray diffraction patterns of the thin films after annealing. Figure 8 b and Figure 8 c is CsPblBr without temporal annealing 3-x Br x Atomic force micrographs of the thin films after annealing for 5 minutes and 10 minutes at 110 °C. Figure 8 d is CsPblBr without temporal annealing 3-x Br x Transmission electron micrograph of the thin film. Figure 8 e and Figure 8 f is CsPblBr without temporal annealing 3-x Br x Characterization of the internal lattice plane defects of the thin film.

[0028] Figure 9 CsPblBr with only amino acid added with temporal annealing 3-x Br x Thin film phase and morphology analysis. Among them, Figure 9 a and Figure 9 b is CsPblBr with only amino acid added 3-x Br x X-ray diffraction patterns of the thin films after annealing at 90 °C and 120 °C. Figure 9 c- Figure 9 e is CsPblBr with only amino acid added 3-x Br x Atomic force micrographs of the thin films after annealing at 90 °C for 2 minutes, 5 minutes and 10 minutes. Figure 9 f is CsPblBr without temporal annealing 3-x Br x Transmission electron micrograph of the thin film. Figure 9 g and Figure 9 h is CsPblBr without temporal annealing 3-x Brx Characterization of lattice internal plane defects of thin films.

[0029] Figure 10 Mixed halide CsPbI3 induced by inhomogeneous halogen distribution 3-x Br x Schematic diagram of internal plane defects of perovskite. Wherein, Figure 10 a is atomically resolved CsPbI3 3-x Br x Spherical aberration electron microscopy of thin films. Figure 10 b is a dose analysis of the spherical aberration electron microscopy at the plane defect site for identifying halide ion species. Figure 10 c is the halide ion arrangement at the defect site obtained from Figure 10 b results. Figure 10 d is mixed halide CsPbI3 3-x Br x Schematic diagram of lattice plane defect formation in thin films.

[0030] Figure 11 Lattice characterization of perovskite thin films without plane defects regulated by liquid-liquid phase separation. Wherein, Figure 11 a and Figure 11 b is CsPbI3 3-x Br x Lattice characterization of thin films. Figure 11 c is a schematic diagram of homogenizing halide ions by liquid-liquid phase separation and eliminating plane defects. DETAILED DESCRIPTION

[0031] In order for those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application.

[0032] All raw materials of the present application have no special restrictions on their sources, and can be purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0033] The raw materials used in the present application have no special restrictions on their purity, and the present application preferably has analytical purity or conventional purity in the field of perovskite material preparation.

[0034] All materials of the present application have conventional grades and abbreviations in the art, and each grade and abbreviation is clear and explicit in its related field of use. Those skilled in the art can purchase or prepare them by conventional methods according to the grade, abbreviation and corresponding use.

[0035] All the processes and their abbreviations in the present application are the conventional abbreviations in the field, and each abbreviation is clear and explicit in the field of its relevant use, and the skilled person in the field can understand the conventional process steps according to the abbreviation.

[0036] In the following examples, the methods used are conventional methods in the field unless otherwise specified, and the materials, reagents, detection devices, etc. used can be obtained from commercial channels.

[0037] Please refer to Figure 1 The fluorine-containing polymer regulated mixed halide perovskite film preparation method shown in the figure comprises the following steps:

[0038] S1, according to the proportion, the perovskite precursor is weighed, dissolved in the first solvent to form a mixed solvent, and the amino acid ligand for guiding the perovskite oriented crystallization process is added to the mixed solvent, heated and stirred at 60°C for one hour to form a uniform and clear perovskite precursor solution.

[0039] It should be noted that the general formula of the perovskite is ABX3; wherein the A-site ion is one or more of cesium ion, formamidinium ion and methylamine ion; the B-site ion is lead ion and / or tin ion; the X-site ion is one or more of chloride ion, bromide ion and iodide ion; the amino acid ligand is one or more of glycine, serine, arginine, histidine, cysteine and methionine, etc. The first solvent includes one or more of N,N-dimethylformamide, dimethyl sulfoxide and N-methyl pyrrolidone.

[0040] In this embodiment, an electronic balance is used to weigh the perovskite precursor and the amino acid ligand, wherein the perovskite precursor includes cesium iodide (CsI, Xi'an Baolai, anhydrous grade, purity 99.99%), cesium bromide (CsBr, Xi'an Baolai, anhydrous grade, purity 99.99%), lead iodide (PbI2, Xi'an Baolai, anhydrous grade, purity 99.99%), lead bromide (PbBr2, Xi'an Baolai, anhydrous grade, purity 99.99%); the amino acid ligand uses arginine (L-Arg, Aladdin, anhydrous grade, 99.8%). In this embodiment, the molar mass ratio of cesium iodide, cesium bromide, lead iodide, lead bromide and arginine is 0.12 mmol:0.025 mmol:0.037 mmol:0.06 mmol, and the first solvent uses N,N-dimethylformamide (DMF, Sigma-Aldrich, 99.8%).

[0041] It can be understood that the amino acid ligand contains functional groups such as amino and carboxyl groups, which can coordinate with the B-site metal ions (such as Pb 2+ , Sn 2+) form coordination bonds. This coordination can stabilize the perovskite structure and reduce the density of internal defect states. For example, amino acid ligands bind to uncoordinated metal ions on the perovskite surface, reducing surface dangling bonds, suppressing carrier recombination at the surface, and improving material stability and carrier transport performance.

[0042] At the same time, during the crystallization of the perovskite precursor solution, the amino acid ligand can act as a template or directing agent. It can affect the growth direction, size and morphology of perovskite grains. For example, by interacting with perovskite precursor ions, it promotes grain growth along specific crystal planes, forming uniformly oriented and sized grains, optimizing film quality, and thus improving the performance of perovskite devices such as solar cells and light-emitting diodes.

[0043] In addition, the amino acid ligand can also modify the interface between the perovskite and other functional layers such as the electron transport layer and the hole transport layer. Its functional groups can interact with the interface material, improving the interface contact, enhancing the extraction and transport efficiency of carriers at the interface, and reducing the charge load at the interface, thus improving the overall performance of the device.

[0044] S2, a first mass concentration of fluorine-containing polymer is added to the perovskite precursor solution to obtain a fluorine-containing polymer perovskite precursor solution.

[0045] It should be noted that the fluorine-containing polymer in the present embodiment includes one or more of polyperfluoroethylene propylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, perfluoroalkoxy resin, polytrifluorochloroethylene, fluorine-containing polyimide, fluorine-containing polyurethane, amorphous fluoropolymer, and perfluoropolyether. The ratio of the fluorine-containing polymer to the perovskite precursor is (0.02-0.06):1 based on the total mass of the perovskite precursor components. In the present embodiment, the fluorine-containing polymer is a polyvinylidene fluoride (PVDF) solution, and the first mass concentration is 4%wt.

[0046] S3, the fluorine-containing polymer perovskite precursor solution is subjected to film formation treatment on the substrate to form a liquid film, and then subjected to time-sharing annealing treatment to form a micron-sized phase separation region under the initiation of the fluorine-containing polymer, resulting in liquid-liquid separation, and obtaining a fluorine-containing polymer-regulated mixed halide perovskite thin film after cooling.

[0047] It should be noted that the film formation treatment includes one or more of spin coating, blade coating and drop coating. The time-sharing annealing includes low-temperature annealing and high-temperature annealing. The low-temperature annealing temperature is 40-100°C, and the low-temperature annealing time is 1-20 minutes; the high-temperature annealing temperature is 100-130°C, and the high-temperature annealing time is 1-200 minutes.

[0048] Specifically, in the present embodiment, the fluorine-containing polymer perovskite precursor solution is spin-coated at a speed of 8000 revolutions per second for 50 seconds, and then annealed at 90℃ for 10 minutes and at 120℃ for 5 minutes in time annealing.

[0049] The experimental instruments used in the present embodiment for spin-coating and heating annealing of the fluorine-containing polymer perovskite precursor solution include a Jiangsu Leibo spin coater, a German IkA magnetic heating stirrer, a Suzhou Weige nitrogen glove box, and a Japanese Hamamatsu fluorescence quantum yield instrument.

[0050] It can be understood that, in the present embodiment, the high electronegativity (4.0) of the fluorine atom in the fluorine-containing polymer forms a strong polar site in the polymer chain, and this electrostatic anchoring effect can stabilize the perovskite crystal nucleus and inhibit the initial disordered growth of the crystal. Moreover, the fluorine-containing side chain (such as -CF3, -CF2-) endows the polymer with low surface energy characteristics, and the polymer can spontaneously migrate to the gas-liquid interface to form a dynamic self-assembled layer in the solution state. This characteristic allows the polymer to continuously adjust the surface tension of the perovskite precursor solution during film formation, promoting the lateral uniform growth of perovskite grains. The strong interaction between the polar C-F bond in the fluoropolymer network and the polar solvent in the perovskite precursor is conducive to the retention of the polar solvent in the perovskite intermediate phase during the time annealing process, allowing the ion components in the film to diffuse uniformly. At the same time, the polymer matrix ultimately exists at the grain boundary position of the perovskite film, which can limit the growth of perovskite grains and improve the film-forming properties of the film, ultimately obtaining a perovskite film with uniform perovskite grain size and no pinholes.

[0051] In addition, the traditional anti-solvent film formation relies on the rapid extraction effect of toluene / chlorobenzene, which is easy to cause the instantaneous supersaturation precipitation of perovskite. In the present embodiment, the fluorine-containing polymer regulates the volatilization kinetics of the precursor solution, allowing the solvent (such as DMF / DMSO) to volatilize in a gradient, inducing the gradual crystallization of perovskite and forming a dense and pinhole-free film structure. Omitting the use of anti-solvent not only eliminates the emission of volatile organic solvents, but also avoids the side reactions of anti-solvents with perovskite precursors.

[0052] The following will be described in detail Figures 2 to 7 Specifically, in the present embodiment, the fluorine-containing polymer PVDF with different molecular weights is added to regulate the liquid-liquid phase separation process of the mixed halide perovskite intermediate phase. At the same time, the liquid-liquid phase separation process of the perovskite intermediate phase is indeed explained at the macroscopic scale. The present application uses X-ray diffraction to test the phase of the film, and uses atomic force microscopy to explore the liquid film morphology evolution during low-temperature annealing.

[0053] Specifically, in the present embodiment, the fluorine-containing polymer PVDF used has a molecular weight of 18W, 40W and 53W, Figure 2 The crystallization of the perovskite film prepared in the present embodiment during annealing. Figure 3Characterization of the liquid-liquid phase separation process of perovskite thin films.

[0054] like Figure 2 As shown, the perovskite film exhibits a diffraction peak at approximately 4° during low-temperature annealing at 90°C. With further high-temperature annealing, the intermediate phase structure disappears, accompanied by the appearance of perovskite crystallization diffraction peaks. The low-angle diffraction peaks only exist during low-temperature annealing, indicating that the film phase obtained under low-temperature annealing is the intermediate metastable phase of perovskite.

[0055] like Figure 3 As shown, the atomic force microscopy results reveal a continuous liquid-liquid phase separation process occurring inside the film. With increasing annealing time at low temperatures, the crystal domains inside the perovskite film are observed to gradually divide into smoother and smaller domains, which is attributed to phase segregation behavior induced by the fluoropolymer.

[0056] Meanwhile, as the molecular weight of the polymer increases, the degree of phase separation becomes more pronounced. During liquid-liquid phase separation, halide ions inside the gel membrane undergo rapid and uniform distribution.

[0057] Figure 4 For the comparative thin film examples, property analysis was performed. During low-temperature annealing, low-angle diffraction peaks appeared in the perovskite thin films without PVDF. However, these diffraction peaks did not disappear after further high-temperature annealing. No gradual segmentation of regions was observed during the low-temperature annealing process, indicating that phase separation did not occur in the sample without the fluoropolymer.

[0058] Figure 5 The grain size change of the perovskite film after the addition of fluoropolymers is shown. Because the fluoropolymers are distributed at the grain boundaries, they encapsulate the perovskite grains during grain growth, thus limiting their growth. Therefore, the perovskite film with added fluoropolymers exhibits a more uniform grain size distribution and better film formation properties. Furthermore, the grain distribution becomes even more uniform with increasing molecular weight of the fluoropolymer.

[0059] Figure 6 Mixed halogen CsPbI with added PVDF of different molecular weights 3-x Br x - LED device performance diagram. (For example...) Figure 6As shown in FIG. 8a, with the increase of the molecular weight of PVDF, the current density of the perovskite LED device does not decrease significantly, which indicates that the addition of high molecular weight PVDF does not adversely affect the transport performance of the device. It can be found that with the increase of the molecular weight of PVDF, the brightness of the LED device increases and the efficiency of the device improves, which is because with the increase of the molecular weight of PVDF, the defect state density of the perovskite thin film decreases, which reflects that the increase of the degree of phase separation is beneficial to improve the performance of the device.

[0060] The following will be described in combination with Figures 8-11 Further, the synergistic effect of the fluorine-containing polymer, the amino acid and the time-sharing annealing process in the present application is described. The synergistic effect cooperatively regulates the homogenization of halogen ions in the system, and further eliminates the high-latitude plane defects in the halogen perovskite lattice.

[0061] Figure 7 CsPbI 3-x Br x Film phase and morphology analysis, wherein, Figure 7 CsPbI 3-x Br x X-ray diffraction pattern of the film after annealing. Figure 7 b and Figure 7 c is the atomic force microscopy of the perovskite film only added with PVDF after annealing for 5 minutes and 10 minutes at 90°C. Figure 7 d is the transmission electron microscopy of the perovskite film only added with PVDF. Figure 7 e and Figure 7 f is the characterization of the internal lattice defects of the perovskite film only added with PVDF.

[0062] From Figure 7 It can be seen that for the CsPbI 3-x Br x Sample only added with polymer, due to the lack of crystallization regulation and time-sharing annealing regulation of amino acid, the film does not undergo liquid-liquid phase separation process, and the crystallinity of the film is poor and the internal defects of the lattice are more. As shown in Figure 7 a, the perovskite film only added with polymer has poor crystallinity, which reflects that the polymer cannot regulate the crystallization process of the perovskite film. As shown in Figure 7 b and Figure 7 c, under the continuous temperature annealing, the grain morphology of the perovskite film does not change significantly, which reflects that the addition of polymer only cannot regulate the liquid-liquid phase separation process of the mixed halogen perovskite film.

[0063] As shown in Figure 7 d, it can be seen from the transmission electron microscopy of the film that the above perovskite film presents a polycrystalline morphology like cobblestone. As shown in Figure 7 e andFigure 7 Further atomically resolved spherical aberration corrected TEM we found that there are more interplanar defects in the lattice of the mixed halide perovskite which did not undergo liquid-liquid phase separation. Further zoom in the defect site lattice, we found that the interplanar defects are formed by the misorientation of the lead halide octahedral atomic layers, which is the insertion of a shale type of cesium halide lattice in the normal lattice.

[0064] Figure 8 CsPbI 3-x Br x Thin film phase and morphology analysis. Figure 8 a CsPbI 3-x Br x Thin film X-ray diffraction pattern after annealing. Figure 8 b and Figure 8 c CsPbI 3-x Br x Thin film atomic force microscopy after annealing at 110°C for 5 minutes and 10 minutes. Figure 8 d CsPbI 3-x Br x Thin film transmission electron microscopy. Figure 8 e and Figure 8 f CsPbI 3-x Br x Thin film characterization of interplanar defects in the lattice.

[0065] From Figure 8 We can conclude that for perovskite films that did not undergo time-of-flight annealing, there are also a large number of interplanar defects in the lattice due to the absence of a liquid-liquid phase separation process. The perovskite film with the addition of amino acids has good crystallinity. However, at a sustained high temperature, the perovskite film has already had good crystallinity, and during the continuous annealing process, no significant liquid-liquid phase separation process occurs in the film. The results of transmission electron microscopy reflect the characteristics of the polycrystalline film. Further results of atomically resolved spherical aberration corrected TEM reflect that there are more interplanar defects in the lattice of the mixed halide perovskite which did not undergo liquid-liquid phase separation. This reflects that the perovskite film without using time-of-flight annealing process also has a large number of interplanar defects in the film.

[0066] Figure 9 CsPbI 3-x Br x Thin film phase and morphology analysis. Among them, Figure 9 a and Figure 9 b CsPbI 3-x Br xX-ray diffraction patterns of the thin film after annealing at 90℃ and 120℃. Figure 9 c- Figure 9 e represents CsPbI with only added amino acids. 3-x Br x Atomic force microscopy images of the thin film after annealing at 90°C for 2 minutes, 5 minutes, and 10 minutes. Figure 9 f represents the CsPbI₂ without time-division annealing. 3-x Br x Transmission electron microscope image of the thin film. Figure 9 g and Figure 9 h represents CsPbI₂ without time-division annealing. 3-x Br x Characterization of surface defects within the crystal lattice of thin films.

[0067] from Figure 9 It can be seen that for perovskite films with only amino acids added, despite using a time-separated annealing process, no liquid-liquid phase separation occurs during crystallization due to the absence of polymer additives, and numerous surface defects exist within the crystal lattice. The perovskite film with added amino acids exhibits better crystallinity. However, under sustained high-temperature annealing, because the perovskite film already possesses good crystallinity, no significant liquid-liquid phase separation occurs within the film during continuous annealing. Transmission electron microscopy results indicate that this film exhibits characteristics of a polycrystalline film. Further atomic-level aberration-corrected electron microscopy results reveal numerous surface defects within the crystal lattice. This indicates that perovskite films without added polymers also possess a large number of surface defects.

[0068] Figure 10 To induce mixed halogen CsPbI due to uneven halogen distribution 3-x Br x Schematic diagram of internal defects in perovskite crystals.

[0069] from Figure 10 It can be seen that the formation of internal surface defects in perovskite lattices is related to CsPbI. 3-x Br x The uneven distribution of halide ions during thin film crystallization is related. For example... Figure 10 a. Using aberration-corrected electron microscopy dosimetry, we found that the distribution of halide ions at defect sites is highly uneven, indicating that surface defects are closely related to the uneven distribution of halide ions during the crystallization of mixed halogens. For example... Figure 10 b, in CsPbI 3-x Br x During thin film crystallization, lattice strain caused by uneven halogen distribution leads to numerous defects in perovskite crystallization. Therefore, to avoid mixed halides CsPbI 3-x Br x The formation of surface defects in perovskite thin films is crucial for promoting the uniform mixing of halide ions.

[0070] Figure 11 Lattice characterization of surface-defect-free perovskite thin films regulated by liquid-liquid phase separation. Figure 11 a and Figure 11 b is CsPbI 3-x Br x Lattice characterization of thin films. Figure 11 c is a schematic diagram illustrating the process of separating and homogenizing halide ions in the liquid-liquid phase, thereby eliminating surface defects.

[0071] from Figure 11 It can be seen that for samples using a time-series annealing process with the simultaneous addition of polymers and amino acids, the liquid-liquid phase separation process in the film facilitates the homogenization of halide ions. Specifically, the surface defects inside the optimized mixed halide perovskite film are effectively eliminated, demonstrating the role of the liquid-liquid phase separation process in homogenizing halide ions. This, in turn, reduces the lattice stress during the perovskite crystallization process, ultimately achieving a perovskite film without surface defects.

[0072] It should be noted that the thin films prepared by the method of the present invention can be applied to fields such as semiconductor light-emitting materials or photovoltaic devices.

[0073] This invention introduces a fluoropolymer into a mixed halide perovskite precursor solution to improve the quality of the mixed halide perovskite film. During low-temperature annealing, the fluoropolymer can initiate in-situ liquid-liquid phase separation within the perovskite film, which is beneficial for the uniform distribution of halide ions within the film. This not only reduces the lattice stress during perovskite crystallization but also effectively reduces film defects, thereby improving the quality of the mixed halide perovskite film and ultimately optimizing the performance of perovskite LED devices.

[0074] The above description is a specific implementation of the embodiments of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a mixed halide perovskite thin film controlled by a fluoropolymer, characterized in that, Includes the following steps: S1. Weigh the perovskite precursor according to the ratio, dissolve it in the first solvent to form a mixed solvent, and add an amino acid ligand to the mixed solvent to guide the perovskite orientation crystallization process. Heat and stir to form a uniform and clear perovskite precursor solution. S2, add a first mass concentration of fluorinated polymer to the perovskite precursor solution to obtain a fluorinated polymer perovskite precursor solution, wherein the fluorinated polymer is polyvinylidene fluoride; S3, a fluorinated polymer perovskite precursor solution is formed on a substrate to form a liquid film, and then time-separated annealing is performed to make the liquid film form a micron-scale phase separation region under the initiation of the fluorinated polymer, resulting in liquid-liquid separation. After cooling, a mixed halide perovskite thin film regulated by fluorinated polymer is obtained. The perovskite in S1 has the general formula ABX3; Wherein, the A-site ion is one or more of cesium ion, formamidinium ion, and methylamine ion; the B-site ion is lead ion and / or tin ion; the X-site ion is one or more of chloride ion, bromide ion, and iodide ion; the amino acid ligand is one or more of glycine, serine, arginine, histidine, cysteine, and methionine; and the first solvent includes one or more of N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone. Based on the molar amount of B-site ions in the perovskite precursor, the molar mass ratio of the amino acid ligand to the perovskite precursor is (0.05-0.2):1; the molecular weight range of the fluoropolymer is 0.6W-100W; the time-sequential annealing includes low-temperature annealing and high-temperature annealing, the low-temperature annealing temperature is 40-100℃, and the low-temperature annealing time is 1-20 minutes; the high-temperature annealing temperature is 100-130℃, and the high-temperature annealing time is 1-200 minutes.

2. The method for preparing mixed halide perovskite thin films controlled by fluoropolymers according to claim 1, characterized in that, The ratio of the fluoropolymer to the perovskite precursor is calculated based on the total mass of the perovskite precursor components, and the mass ratio of the two is (0.02-0.06):

1.

3. The method for preparing mixed halide perovskite thin films controlled by fluoropolymers according to claim 1 or claim 2, characterized in that, The film-forming process includes one or more of spin coating, blade coating, and drop coating.

4. A thin film prepared by the method for preparing mixed halide perovskite thin films controlled by fluoropolymers as described in any one of claims 1-3.

5. The application of the thin film as described in claim 4 in semiconductor light-emitting materials or photovoltaic devices.

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