A method for preparing MAPbBr3 single crystal thin films by spin-coating dimethyl silicone oil in a spatially confined environment and its application.

Abstract

This invention relates to a method for preparing MAPbBr3 single-crystal thin films in a spatially confined environment with spin-coated dimethyl silicone oil and its application, belonging to the field of optoelectronic materials and devices technology. This invention discloses a method for preparing MAPbBr3 single-crystal thin films in a spatially confined environment with spin-coated dimethyl silicone oil, enabling in-situ preparation of MAPbBr3 single-crystal thin films. This invention aims to solve the following problems by introducing a dimethyl silicone oil layer as a top cover: (1) providing a superhydrophobic, low-adhesion interface to achieve easy and non-destructive peeling of the single-crystal thin film; (2) regulating solvent evaporation kinetics to ensure uniform and slow release of the precursor, obtaining a dense, pore-free single-crystal thin film; (3) creating a stable microenvironment in the atmospheric environment that isolates water and oxygen interference for the crystal growth interface; (4) regulating solvent diffusion kinetics to ensure continuous solute supply and avoid insufficient solute to form PbBr2 crystals; and (5) obtaining linearly polarized light emission with a polarization degree of 74%.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic materials and devices technology, and relates to a method for preparing MAPbBr3 single crystal thin films by spin-coating dimethyl silicone oil in a spatially confined environment and its application. Background Technology

[0002] Organic-inorganic metal halide perovskite crystals have attracted much attention as a new generation of optoelectronic materials due to their excellent intrinsic properties (such as wide absorption range, high extinction coefficient, long carrier diffusion length, and high carrier mobility). To realize their potential for excellent carrier transport performance while considering device performance and fabrication requirements, it is necessary to control the crystal thickness at an appropriate level to balance light absorption and carrier recombination loss. Therefore, the fabrication of perovskite single-crystal thin films with tunable thickness has become a key research direction in this field.

[0003] Among numerous preparation methods, the spatial confinement method has become the most commonly used strategy for preparing perovskite single-crystal thin films with controllable thickness due to its mild conditions, high versatility, and good compatibility with various traditional solution methods (such as inverse crystallization, cooling-induced crystallization, antisolvent vapor-assisted crystallization, and top-seeded solution growth). This method directly restricts the vertical growth direction of the crystal by confining the precursor solution within a geometrically restricted space formed by two substrates, thus successfully transforming bulk perovskite crystals into thin film form.

[0004] However, in addition to being highly sensitive to water and oxygen, perovskite single-crystal thin films also face three major bottlenecks: First, strong interfacial adhesion, which can easily lead to film tearing or even being carried away by the top cover plate during peeling off of rigid substrates; second, difficulty in mass transfer control, with uneven solvent evaporation and low ion transport efficiency in static confined spaces, easily resulting in defects such as pores and cracks; and third, poor environmental stability, with water and oxygen interfering with crystallization kinetics in humid environments, leading to disordered crystallization and quality degradation. Furthermore, the reliance on inert atmospheres or vacuum environments results in high equipment costs, complex operation, and difficulty in large-scale production. Therefore, how to simultaneously solve the problems of interfacial adhesion, mass transfer control, and environmental stability in open environments or under non-inert gas protection, and to prepare high-quality perovskite single-crystal thin films with consistent orientation and large grain size, remains a key technological bottleneck that urgently needs to be overcome in this field.

[0005] (2) Briefly describe the existing technical solutions related to this invention; Currently, existing technologies for preparing perovskite single-crystal thin films based on spatial confinement mainly revolve around the control of growth conditions within the confined space. Specifically, they can be summarized into the following three strategy directions: (1) Thickness control strategy, which achieves precise adjustment of film thickness by controlling the spacing between two substrates. A typical method is to use polytetrafluoroethylene film as a spacer. By selecting spacers of different thicknesses, single-crystal thin films with millimeter-level thicknesses can be obtained. To obtain thinner μm-level or even nm-level films, researchers further introduce external pressure by applying mechanical loads to the substrate to compress the confined space, thereby achieving fine control of film thickness from millimeter-level to nanometer-level. (2) Size expansion strategy, which aims to suppress random nucleation behavior to obtain large-area continuous single-crystal thin films, mainly using the seed crystal induction method. Specifically, by introducing pre-prepared perovskite seed crystals into the confined space, or by using a temperature gradient to artificially create supersaturated conditions at the top interface to induce crystal nucleus formation, non-uniform random nucleation can be effectively suppressed, thereby achieving the growth of large-area single-crystal thin films from millimeters to centimeters. In addition, substrate surface treatment is also used to control the nucleation position. For example, hydrophobic treatment is applied to one side of the substrate to increase the nucleation barrier, and hydrophilic treatment is applied to the other side to reduce the nucleation barrier, thereby achieving in-situ selective growth of the thin film on the target substrate; (3) Quality and structure optimization strategy: In order to maintain the continuous growth of the crystal and avoid size limitations caused by the consumption of precursors, a dynamic flow reaction system was developed. The system drives the precursor solution to continuously circulate in a confined space through a pump, constantly replenishing the consumed precursor ions, thereby supporting the continuous lateral growth of the crystal and finally obtaining a high-quality, large-size single crystal thin film.

[0006] The current state of development in this field is as follows: Organic-inorganic metal halide perovskite crystals, as a new generation of optoelectronic materials, have attracted much attention due to their excellent intrinsic properties (such as wide absorption range, high extinction coefficient, long carrier diffusion length, and high carrier mobility). To realize their potential for excellent carrier transport performance while considering device performance and fabrication requirements, it is necessary to control the crystal thickness at an appropriate level to balance light absorption and carrier recombination loss. Therefore, the fabrication of perovskite single-crystal thin films with adjustable thickness has become a key research direction in this field. Among many fabrication methods, the spatial confinement method has become the most commonly used strategy for fabricating perovskite single-crystal thin films with controllable thickness due to its mild conditions, strong universality, and good compatibility with various traditional solution methods (such as inverse temperature crystallization, cooling-induced crystallization, antisolvent vapor-assisted crystallization, and top seed crystal solution growth). This method directly restricts the vertical growth direction of the crystal by confining the precursor solution within a geometrically confined space formed by two substrates, thereby successfully transforming bulk perovskite crystals into thin film form. However, in addition to being highly sensitive to water and oxygen, perovskite single-crystal thin films also face three major bottlenecks: First, strong interfacial adhesion, which can easily lead to film tearing or even being carried away by the cover plate during peeling off of rigid substrates; second, difficulty in mass transfer control, with uneven solvent evaporation and low ion transport efficiency in static confined spaces, easily resulting in defects such as pores and cracks; and third, poor environmental stability, with water and oxygen interfering with crystallization kinetics in humid environments, leading to disordered crystallization and quality degradation. Furthermore, the reliance on inert atmospheres or vacuum environments results in high equipment costs, complex operation, and difficulty in large-scale production. Therefore, how to simultaneously solve the problems of interfacial adhesion, mass transfer control, and environmental stability in open environments or under non-inert gas protection, and to prepare high-quality perovskite single-crystal thin films with consistent orientation and large grain size, remains a key technological bottleneck that urgently needs to be overcome in this field.

[0007] Currently, existing technologies for preparing perovskite single-crystal thin films based on spatial confinement mainly revolve around the control of growth conditions within the confined space. Specifically, they can be summarized into the following three strategy directions: (1) Thickness control strategy, which achieves precise adjustment of film thickness by controlling the spacing between two substrates. A typical method is to use polytetrafluoroethylene film as a spacer. By selecting spacers of different thicknesses, single-crystal thin films with millimeter-level thicknesses can be obtained. To obtain thinner μm-level or even nm-level films, researchers further introduce external pressure by applying mechanical loads to the substrate to compress the confined space, thereby achieving fine control of film thickness from millimeter-level to nanometer-level; (2) Size expansion strategy, which aims to suppress random nucleation behavior to obtain large-area continuous single-crystal thin films, mainly using the seed crystal induction method. Specifically, by introducing pre-prepared perovskite seed crystals into the confined space, or by using a temperature gradient to artificially create supersaturated conditions at the top interface to induce crystal nucleus formation, non-uniform random nucleation can be effectively suppressed, thereby achieving the growth of large-area single-crystal thin films from millimeters to centimeters. In addition, substrate surface treatment is also used to control the nucleation location. For example, hydrophobic treatment is applied to one side of the substrate to increase the nucleation barrier, and hydrophilic treatment is applied to the other side to reduce the nucleation barrier, thereby achieving in-situ selective growth of the thin film on the target substrate; (3) Quality and structure optimization strategy: In order to maintain the continuous growth of the crystal and avoid size limitations caused by the consumption of precursors, a dynamic flow reaction system was developed. The system drives the precursor solution to continuously circulate in a confined space through a pump, constantly replenishing the consumed precursor ions, thereby supporting the continuous lateral growth of the crystal and finally obtaining a high-quality, large-size single crystal thin film.

[0008] Although significant progress has been made in the preparation of perovskite single-crystal thin films using spatial confinement methods, existing spatial confinement methods, especially for preparing high-quality perovskite single-crystal thin films in atmospheric environments, still have the following key bottlenecks, which directly correspond to the problems that this invention aims to solve: (1) Interface adhesion and film damage problems: In existing methods, the upper and lower substrates are mostly rigid materials (such as hydrophobic polyethylene terephthalate, trichloro(1H,1H,2H,2H-perfluorooctyl) silane). In order to achieve the transfer or device construction after film growth, it is usually necessary to perform complex surface modifications on the substrate (such as hydrophobization) or rely on the difference in interaction forces between the substrates. However, when removing the top cover plate, the perovskite crystal and the cover plate may still have strong adhesion due to van der Waals forces or chemical effects, which leads to the tearing of the crystal film surface during the peeling process, introducing a large number of defects and destroying its integrity. (2) Mass transfer limitations and defect formation: Static confined space severely limits solvent evaporation and long-range transport efficiency of precursor ions, easily leading to local concentration inhomogeneity and the formation of non-perovskite phases. Although dynamic flow systems improve mass transfer, they increase equipment complexity and cost. In addition, in atmospheric environments, uneven solvent evaporation is more likely to cause sudden changes in local supersaturation, thereby forming macroscopic defects such as pores and cracks in the film. (3) Atmospheric environment stability challenges: Existing strategies are mostly implemented in controlled atmospheres or glove boxes, which are not sufficiently adaptable to atmospheric environments (especially humidity). Water and oxygen in the atmosphere can seriously interfere with the crystallization kinetics of perovskite, leading to increased nonradiative recombination and decreased crystal quality. Existing methods lack simple means to provide a continuous and stable protective microenvironment for crystal growth in open environments. (4) Low polarization degree of linearly polarized light: Existing perovskite single crystal films prepared based on spatial confinement methods produce linearly polarized light with low polarization degree. To date, only two single-crystal thin films (CsPbBr3 and MAPbBr3) have been reported in the literature, with linear polarization degrees of 50% and 69%, respectively. In contrast, this invention, through optimized fabrication process (improving interfacial adhesion, suppressing mass transfer limitation, and enhancing atmospheric adaptability), successfully obtained a single-crystal thin film with a linear polarization degree of 74%, providing a superior technical solution for the fabrication of highly anisotropic single-crystal thin films.

[0009] To address the core challenges of existing spatial confinement methods for preparing perovskite single-crystal thin films in atmospheric environments, such as strong interfacial adhesion, difficulty in mass transfer control, poor environmental stability, and low linear polarization, this invention proposes a method for preparing MAPbBr3 single-crystal thin films in a spatially confined environment assisted by spin-coating dimethyl silicone oil. This method facilitates the formation of single crystals, yields crystals with low interfacial defect state density, few interfacial pores, and high repeatability. Moreover, the prepared MAPbBr3 perovskite single-crystal thin films exhibit an orange square flake shape and possess three-dimensional semiconductor optical properties, with a fluorescence emission wavelength of 550 nm, making them promising candidates for preparing perovskite single-crystal thin-film light-emitting diodes.

[0010] Therefore, it is necessary to continue researching a simple, efficient, and low-cost method for the controllable preparation of high-quality, large-size perovskite single-crystal thin films in an atmospheric environment. Summary of the Invention

[0011] In view of this, one objective of the present invention is to provide a method for preparing MAPbBr3 single crystal thin films by spin-coating dimethyl silicone oil in a spatially confined environment; a second objective of the present invention is to provide a MAPbBr3 single crystal thin film prepared by the method for preparing MAPbBr3 single crystal thin films by spin-coating dimethyl silicone oil in a spatially confined environment; and a third objective of the present invention is to provide an application of MAPbBr3 single crystal thin films in linearly polarized luminescence.

[0012] To achieve the above objectives, the present invention provides the following technical solution: 1. A method for preparing MAPbBr3 single-crystal thin films by spin-coating dimethyl silicone oil with spatial confinement, the method comprising the following steps: (1) Coating the lower substrate with poly(9-ethylenecarbazole): A poly(9-ethylenecarbazole) solution is dropped onto the surface of the pretreated ITO substrate, and after spin coating, it is annealed to obtain a lower substrate coated with poly(9-ethylenecarbazole). (2) Top cover plate coated with silicone oil: Dimethyl silicone oil solution is uniformly coated on the surface of another pretreated ITO substrate, and after spin coating, annealing is performed to obtain a top cover plate coated with dimethyl silicone oil. (3) Assemble the confined space: Cover the lower substrate coated with poly(9-ethylene carbazole) with a top cover plate coated with dimethyl silicone oil, wherein the surface of the top cover plate coated with dimethyl silicone oil is in contact with the poly(9-ethylene carbazole) surface of the lower substrate. Use dovetail clips to control the distance between the top cover plate and the lower substrate to be 10-100 μm, thus forming a confined growth space between the top cover plate and the lower substrate. (4) Precursor solution injection: The MAPbBr3 precursor solution is dropped into the confined growth space and the solution is spread throughout the confined growth space by capillary action to obtain the assembled sample. (5) Atmospheric environment growth: The assembled sample is placed on a heating stage in an atmospheric environment for crystal growth until the solvent is completely evaporated; (6) Separation and post-processing: After the solvent has completely evaporated, transfer it to the glove box environment, remove the dovetail clip, let it stand for 2 to 12 hours, and then separate the top cover plate. MAPbBr3 single crystal thin film can be prepared in situ on the lower substrate.

[0013] Preferably, in step (1), the pretreatment method of the substrate is as follows: the ITO substrate is ultrasonically cleaned with acetone, anhydrous ethanol, deionized water and acetone solution for 20 min each, then dried at 100 °C for 5 min, and finally placed in an ultraviolet-ozone cleaner for ozone treatment. The ITO substrate measures 14.9 × 15.1 mm. 2 ; In step (1), the spin coating speed is 4000 rpm and the time is 60 s; In step (1), the annealing temperature is 150 °C and the time is 15 min.

[0014] Preferably, in step (1), the poly(9-vinylcarbazole) solution is prepared by adding chlorobenzene to poly(9-vinylcarbazole) solid powder and stirring for at least 12 hours. The volume-to-mass ratio of the chlorobenzene and poly(9-ethylenecarbazole) solid powder is 2:12, mL:mg.

[0015] Preferably, in step (2), the dimethyl silicone oil solution is prepared by adding silicone oil to toluene and stirring for at least 12 hours, wherein the viscosity of the silicone oil at 25°C is 160±10 mPa.s, and the volume ratio of the silicone oil to toluene is 50:10, μL:mL; In step (2), the spin coating speed is 4000 rpm and the time is 60 s; In step (2), the annealing temperature is 120 °C and the time is 15 min.

[0016] Preferably, in step (4), the preparation method of the MAPbBr3 perovskite precursor solution is as follows: methyl ammonium bromide (MABr), lead bromide (PbBr2) and polyvinylpyrrolidone solid powder are mixed and then added to N,N-dimethylformamide solution, and stirred for no less than 12 h to obtain the MAPbBr3 perovskite precursor solution.

[0017] The polyvinylpyrrolidone has an Mw of 1,300,000; The mass-to-volume ratio of the solid powders of methylammonium bromide (MABr), lead bromide (PbBr2), and polyvinylpyrrolidone is 93.87:294.11:5:0.5, mg:mg:mg:mL.

[0018] Preferably, in step (5), the heating table has a heating rate of 5 ℃ / h, the relative humidity of the environment is 60~80%, and the temperature of the environment is 15~30 ℃; In step (5), the crystal is allowed to stand for 12 to 72 hours to allow the solvent to evaporate naturally during growth. 2. The MAPbBr3 single crystal thin film prepared by the above method.

[0019] 3. Applications of the above-mentioned MAPbBr3 single crystal thin films in online polarization luminescence The beneficial effects of this invention are as follows: This invention discloses a method for preparing MAPbBr3 single crystal thin films in situ using spin-coated dimethyl silicone oil-assisted spatial confinement. This invention aims to solve the following problems by introducing a dimethyl silicone oil layer as a top cover: (1) providing a superhydrophobic, low-adhesion interface to achieve easy and non-destructive peeling of the single crystal thin film; (2) regulating solvent evaporation kinetics to ensure uniform and slow release of the precursor, resulting in a dense, pore-free single crystal thin film; (3) creating a stable microenvironment in the atmosphere that isolates water and oxygen interference for the crystal growth interface; (4) regulating solvent diffusion kinetics to ensure continuous solute supply and avoid insufficient solute to form PbBr2 crystals; (5) obtaining linearly polarized light emission with a polarization degree of 74%.

[0020] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0021] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 The contact angle of the MAPbBr3 precursor solution prepared in Example 1 on the surface of a dimethyl silicone oil film; Figure 2 This is a diagram showing the diffusion process of the MAPbBr3 precursor solution prepared in Example 1 within a confined space. Figure 3 The 2×3mm specimens were grown in an atmospheric environment using a dimethyl silicone oil-assisted spatial confinement method, as described in Example 1. 2MAPbBr3 perovskite single crystal thin film; Figure 4 The top cover plate that was peeled off after crystal growth was completed; Figure 5 The image shows the surface morphology of the MAPbBr3 perovskite single crystal thin film prepared in Example 1 under a scanning electron microscope. Figure 6 The steady-state absorption spectrum of the MAPbBr3 single-crystal thin film prepared in Example 1 is shown. Figure 7 The photoluminescence spectrum of the MAPbBr3 single-crystal thin film prepared in Example 1 is shown; Figure 8 The X-ray diffraction pattern of the MAPbBr3 single crystal thin film prepared in Example 1 is shown. Figure 9 Image a is a schematic diagram of the apparatus for testing the linear polarization degree of the MAPbBr3 single crystal thin film prepared in Example 1, and image b is the fluorescence intensity distribution of the MAPbBr3 single crystal thin film prepared in Example 1 at different angles. Figure 10 This invention describes the complete process of preparing MAPbBr3 perovskite single-crystal thin films in an atmospheric environment using a spin-coated dimethyl silicone oil-assisted spatial confinement method. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] The chemical reagents used in the in-situ preparation of MAPbBr3 single crystal thin films in the following examples were purchased from a procurement platform. The types, specifications, manufacturers, and proportions of various chemical reagents are shown in Table 1 below: Table 1. Types, specifications, manufacturers, and proportions of chemical reagents

[0024] Methylammonium bromide (MABr) and lead bromide (PbBr2) are both white solid powders and are precursors for the synthesis of MAPbBr3 perovskite. Additionally, MABr provides methylamine cations (MA... + ) and bromide ions (Br -PbBr2 provides lead ions (Pb²⁻) + ) and bromide ions (Br - Dissolving both in N,N-dimethylformamide at a stoichiometric ratio yields a MAPbBr3 perovskite precursor solution.

[0025] Example 1 A method for preparing MAPbBr3 single-crystal thin films by spin-coating dimethyl silicone oil with spatial confinement, the specific steps of which are as follows: Dimethyl silicone oil solution and poly(9-ethylenecarbazole) solution were spin-coated onto cleaned ITO substrates, serving as interface modification layers for the upper cover and lower substrate, respectively. The lower substrate was treated as follows: 70 μL of a 6 mg / mL poly(9-ethylenecarbazole) solution was dropped onto the pretreated ITO lower substrate surface, and spin-coated at 4000 rpm for 60 s. The upper cover was treated as follows: a dimethyl silicone oil solution prepared by mixing dimethyl silicone oil and toluene at a volume ratio of 1:200 was uniformly coated onto the ITO surface of the upper cover, and spin-coated at 4000 rpm for 60 s.

[0026] (2) The spin-coated substrate is placed on a pre-set heating table for annealing. The annealing conditions for poly(9-ethylenecarbazole) film are 150 °C for 15 minutes and for dimethyl silicone oil film are 120 °C for 15 minutes.

[0027] (3) After annealing, the upper cover plate and the lower substrate are assembled. The upper cover plate coated with dimethyl silicone oil film is placed on the lower substrate coated with poly(9-ethylene carbazole) layer. Pressure is applied by dovetail clamps to form a confined growth space with a spacing of 10-100 μm.

[0028] (4) Using a syringe, add MAPbBr3 precursor solution to the gap in the confined growth space, and use capillary action to inject the solution and fill the entire confined space.

[0029] (5) The sample after injecting the precursor was placed on a temperature-controlled heating stage for growth at a rate of 5 °C / hour. After reaching 50 °C, the temperature was kept constant. As the temperature gradually increased, the N,N-dimethylformamide solvent slowly evaporated, and the precipitation and growth of crystals could be observed.

[0030] (6) After the growth is complete, carefully separate the top cover plate to obtain a MAPbBr3 perovskite single crystal film on the bottom substrate.

[0031] Example 2 A method for preparing MAPbBr3 single-crystal thin films by spin-coating dimethyl silicone oil with spatial confinement, the specific steps of which are as follows: (1) ITO substrate pretreatment: The ITO substrate (14.9 × 15.1 mm) was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, deionized water and acetone solution. 2 Each of the pretreated ITO substrates is dried for 20 minutes at 100 °C for 5 minutes, and then placed in an ultraviolet-ozone cleaning machine for ozone treatment to obtain the pretreated ITO substrate. (2) Coating the lower substrate with poly(9-ethylenecarbazole): A poly(9-ethylenecarbazole) solution (chlorobenzene is added to poly(9-ethylenecarbazole) solid powder at a volume mass ratio of 2:12, mL:mg, and stirred for no less than 12h to obtain a poly(9-ethylenecarbazole) solution) is added dropwise to the surface of the pretreated ITO substrate. After spin coating (4000 rpm, 60 s), the substrate is annealed (150 ℃, 15 min) to obtain a lower substrate coated with poly(9-ethylenecarbazole). (3) Coating the top cover plate with silicone oil: uniformly coat the surface of another pretreated ITO substrate with dimethyl silicone oil solution (the dimethyl silicone oil solution is prepared by adding silicone oil (viscosity of 160±10 mPa.s at 25℃) to toluene at a volume ratio of 50:10, μL:mL and stirring for no less than 12h), spin coat (speed of 4000 rpm, time of 60 s), and then anneal (temperature of 120 ℃, time of 15 min) to obtain the top cover plate coated with dimethyl silicone oil; (4) Assemble the confined space: Cover the lower substrate coated with poly(9-ethylene carbazole) with a top cover plate coated with dimethyl silicone oil, wherein the surface of the top cover plate coated with dimethyl silicone oil is in contact with the poly(9-ethylene carbazole) surface of the lower substrate. Use dovetail clips to control the distance between the top cover plate and the lower substrate to be 10 μm, thus forming a confined growth space between the top cover plate and the lower substrate. (5) Precursor solution injection: The MAPbBr3 precursor solution (the preparation method of the MAPbBr3 precursor solution is as follows: methyl ammonium bromide (MABr), lead bromide (PbBr2) and polyvinylpyrrolidone solid powder with Mw=1.300,000 are mixed according to the mass-volume ratio of 93.87:294.11:5:0.5, mg:mg:mg:mL and then N,N-dimethylformamide solution is added and stirred for no less than 12h to obtain the MAPbBr3 perovskite precursor solution) is added dropwise to the confined growth space. The solution is spread throughout the confined growth space by capillary action to obtain the assembled sample; (6) Atmospheric environment growth: The assembled sample is placed on a heating table in an atmospheric environment (heating rate of 5℃ / h, relative humidity of the environment of 60%, and temperature of the environment of 15℃) for crystal growth until the solvent is completely evaporated. (7) Separation and post-processing: After the solvent has completely evaporated, transfer it to the glove box environment, remove the dovetail clip, let it stand for 2 hours, and then separate the top cover plate. MAPbBr3 single crystal thin film can be prepared in situ on the lower substrate.

[0032] Example 3 A method for preparing MAPbBr3 single-crystal thin films by spin-coating dimethyl silicone oil with spatial confinement, the specific steps of which are as follows: (1) ITO substrate pretreatment: The ITO substrate (14.9 × 15.1 mm) was ultrasonically cleaned sequentially with acetone, anhydrous ethanol, deionized water and acetone solution. 2 Each of the pretreated ITO substrates is dried for 20 minutes at 100 °C for 5 minutes, and then placed in an ultraviolet-ozone cleaning machine for ozone treatment to obtain the pretreated ITO substrate. (2) Coating the lower substrate with poly(9-ethylenecarbazole): A poly(9-ethylenecarbazole) solution (chlorobenzene is added to poly(9-ethylenecarbazole) solid powder at a volume mass ratio of 2:12, mL:mg, and stirred for no less than 12h to obtain a poly(9-ethylenecarbazole) solution) is added dropwise to the surface of the pretreated ITO substrate. After spin coating (4000 rpm, 60 s), the substrate is annealed (150 ℃, 15 min) to obtain a lower substrate coated with poly(9-ethylenecarbazole). (3) Coating the top cover plate with silicone oil: uniformly coat the surface of another pretreated ITO substrate with dimethyl silicone oil solution (the dimethyl silicone oil solution is prepared by adding silicone oil (viscosity of 160±10 mPa.s at 25℃) to toluene at a volume ratio of 50:10, μL:mL and stirring for no less than 12h), spin coat (speed of 4000 rpm, time of 60 s), and then anneal (temperature of 120 ℃, time of 15 min) to obtain the top cover plate coated with dimethyl silicone oil; (4) Assemble the confined space: Cover the lower substrate coated with poly(9-ethylene carbazole) with a top cover plate coated with dimethyl silicone oil, wherein the surface of the top cover plate coated with dimethyl silicone oil is in contact with the poly(9-ethylene carbazole) surface of the lower substrate, and the distance between the top cover plate and the lower substrate is controlled to be 100 μm with dovetail clips, thus forming a confined growth space between the top cover plate and the lower substrate. (5) Precursor solution injection: The MAPbBr3 precursor solution (the preparation method of the MAPbBr3 precursor solution is as follows: methyl ammonium bromide (MABr), lead bromide (PbBr2) and polyvinylpyrrolidone solid powder with Mw=1.300,000 are mixed according to the mass-volume ratio of 93.87:294.11:5:0.5, mg:mg:mg:mL and then N,N-dimethylformamide solution is added and stirred for no less than 12h to obtain the MAPbBr3 perovskite precursor solution) is added dropwise to the confined growth space. The solution is spread throughout the confined growth space by capillary action to obtain the assembled sample; (6) Atmospheric environment growth: The assembled sample is placed on a heating table in an atmospheric environment (heating rate of 5℃ / h, relative humidity of the environment of 80%, and temperature of the environment of 30℃) for crystal growth until the solvent is completely evaporated. (7) Separation and post-processing: After the solvent has completely evaporated, transfer it to the glove box environment, remove the dovetail clip, let it stand for 12 hours and then separate the top cover plate to obtain MAPbBr3 single crystal thin film in situ on the lower substrate.

[0033] Performance testing Figure 1 The contact angle of the MAPbBr3 precursor solution prepared in Example 1 on the surface of a dimethyl silicone oil film. From... Figure 1 It can be seen that the contact angle of the MAPbBr3 precursor solution on the surface of the dimethyl silicone oil film is 68°, which is moderate. This moderate contact angle indicates that the dimethyl silicone oil layer has both good hydrophobic barrier properties and wetting and spreading ability, which is a key interfacial factor that enables the precursor solution to diffuse rapidly in a confined space.

[0034] Figure 2 This is a diagram showing the diffusion process of the MAPbBr3 precursor solution prepared in Example 1 within a confined space. From... Figure 2 As can be seen, the lower substrate is poly(9-ethylenecarbazole) modified glass, and the upper cover is dimethyl silicone oil modified glass, with a gap of 10–100 μm. Under capillary action, the solution propagates rapidly, completing diffusion in just 7.05 s, indicating that the silicone oil-modified interface effectively reduces flow resistance. This advantage facilitates the rapid and uniform spreading of the precursor solution on a large-area substrate, laying the foundation for the fabrication of large-size single-crystal thin films.

[0035] Figure 3 The 2×3mm specimens were grown in an atmospheric environment using a dimethyl silicone oil-assisted spatial confinement method, as described in Example 1. 2 MAPbBr3 perovskite single-crystal thin films. From Figure 3It can be clearly seen that there is an orange rectangular MAPbBr3 perovskite single crystal film between the two ITO glasses, indicating that the preparation method of MAPbBr3 perovskite single crystal film of the present invention can effectively suppress random nucleation and promote the lateral growth of crystals, thereby obtaining a perovskite single crystal film with larger size and continuity.

[0036] Figure 4 This is the top cover plate that was peeled off after crystal growth was complete. Figure 4 As can be seen, there are almost no residual crystals on the top cover plate, indicating that the coated dimethyl silicone oil layer can effectively reduce the interfacial adhesion between the perovskite crystals and the top cover plate, and can achieve non-destructive separation of the crystals.

[0037] Figure 5 This is a surface morphology image of the MAPbBr3 perovskite single-crystal thin film prepared in Example 1, obtained using a scanning electron microscope. Figure 5 It can be seen that the MAPbBr3 perovskite single crystal film prepared in Example 1 has no obvious grain boundaries, indicating that it is a single crystal and the crystal surface is smooth and dense, without obvious pores, cracks and peeling damage, which confirms the stress buffering and non-destructive separation effect of the silicone oil layer used in the preparation method of the present invention.

[0038] Figure 6 The steady-state absorption spectrum of the MAPbBr3 single-crystal thin film prepared in Example 1 is shown. From Figure 6 As can be seen, a flat absorption plateau is observed in the visible light wavelength range, with a steep band edge cutoff and no exciton absorption peak characteristics, confirming that the method of the present invention can prepare high-quality single-crystal thin films.

[0039] Figure 7 The photoluminescence spectrum of the MAPbBr3 single-crystal thin film prepared in Example 1 is shown. Figure 7 It can be seen that the emission peak of the MAPbBr3 single crystal thin film prepared in Example 1 is located at 550 nm, corresponding to the band-edge emission of MAPbBr3, and the full width at half maximum (FWHM) is 18.52 nm. The narrow FWHM and symmetrical emission peak shape indicate that the prepared thin film has high crystallinity, low defect density and good compositional uniformity.

[0040] Figure 8 The X-ray diffraction pattern of the MAPbBr3 single-crystal thin film prepared in Example 1 is shown. Figure 8 It can be seen that only the (h00) crystal plane family of equally spaced diffraction peaks appear in the X-ray diffraction pattern, such as Figure 8 The (100), (200), and (300) crystal planes shown in the figure do not exhibit diffraction signals from other crystal planes. This periodic diffraction characteristic indicates that the MAPbBr3 single crystal film prepared by the method of the present invention is a high-quality single crystal with a cubic phase structure and a space group of Pm3m.

[0041] Figure 9 Image a is a schematic diagram of the apparatus for testing the linear polarization degree of the MAPbBr3 single-crystal thin film prepared in Example 1, and image b is the fluorescence intensity distribution of the MAPbBr3 single-crystal thin film prepared in Example 1 at different angles. Figure 9 As can be seen, a 405 nm laser is used as the excitation source to excite the MAPbBr3 single-crystal thin film sample; a linear polarizer is used to control the transmission direction of the emitted light; a 532 nm filter is used to block the 405 nm excitation light while allowing the 550 nm characteristic fluorescence emitted by the sample to pass through; and a silicon probe of the power meter is used to receive the transmitted fluorescence signal. The degree of linear polarization is calculated based on the fluorescence intensity recorded by the silicon probe at different angles, and the calculation formula is as follows: , Indicates the maximum fluorescence intensity. Indicates the minimum fluorescence intensity. From Figure 9 The linear polarization degree of the MAPbBr3 single crystal thin film prepared in Example 1 can be calculated to be 74%.

[0042] Figure 10 The complete process for preparing MAPbBr3 perovskite single crystal thin films in an atmospheric environment based on the spin-coating dimethyl silicone oil-assisted spatial confinement method of the present invention specifically includes the following steps: (1) spin-coating dimethyl silicone oil solution and poly(9-ethylenecarbazole) solution onto a clean ITO substrate, respectively, as interface modification layers for the upper cover plate and the lower substrate; (2) performing annealing treatment to remove residual solvents in the film and promote the densification and stabilization of the film structure; (3) assembling the confinement space and using dovetail clamps to... Pressure is applied to the upper cover plate coated with dimethyl silicone oil and the lower substrate coated with poly(9-ethylenecarbazole) to form a confined growth space with a spacing of 10-100 μm; (4) the MAPbBr3 precursor solution is injected and spread throughout the confined space by capillary action; (5) temperature-controlled growth is carried out by placing the sample after the precursor is injected on a temperature-controlled heating stage to grow crystals and obtain a single crystal film in the confined space; (6) the upper cover plate is separated, that is, a MAPbBr3 perovskite single crystal film is obtained in situ on the lower substrate.

[0043] Therefore, the method for preparing MAPbBr3 single crystal thin films by spin-coating dimethyl silicone oil in a confined space disclosed in this invention has the following advantages: (a) The experimental method is simple and effective, requiring only a conventional spin coater and heating stage; (b) It can be carried out in an atmospheric environment without the need for inert atmosphere protection, significantly reducing equipment costs; (c) The precursor solution diffuses rapidly in the confined space, achieving uniform spreading in just 7.05 s; (d) The prepared perovskite single crystal thin film is of high quality, with XRD showing periodic diffraction peaks of (100), (200), and (300), confirming a cubic phase (Pm3m) single crystal structure; (e) The prepared perovskite single crystal thin film has a smooth and dense surface, free from pores, cracks, and peeling marks; (f) The single crystal thin film has excellent optical properties, with a photoluminescence spectrum half-width of only 18.52 nm and an emission peak at 550 nm. nm, with a steep absorption band edge; (g) achieved non-destructive separation between the top cover plate and the single crystal film, with almost no crystal residue on the surface of the top cover plate after peeling, resulting in a high yield.

[0044] In view of the shortcomings of the existing spatial confinement method for preparing perovskite single crystal thin films, the preparation method of the present invention can solve the following problems: (1) Regarding the problem that "it must be carried out in an inert atmosphere or vacuum environment": the process of growing MAPbBr3 perovskite single crystal thin films in the present invention can be carried out in an atmospheric environment (relative humidity 60~80%, temperature 15~30 ℃). The growth process does not require vacuum equipment or high-purity nitrogen protection. The silicone oil layer forms a dense and hydrophobic physical barrier at the crystal growth interface, effectively isolating water and oxygen interference; (2) Regarding the problem that "the top cover plate is difficult to peel off, which easily leads to film tearing and crystal being taken away": the present invention provides a superhydrophobic and low adhesion interface by coating the top cover plate with a dimethyl silicone oil layer, realizing the non-destructive separation of the single crystal thin film and the top cover plate. After peeling, there are almost no crystal residues on the surface of the top cover plate, and the film is intact; (3) Regarding the problem of "uneven solvent evaporation in static confinement, which easily forms pores and cracks": In this invention, the silicone oil layer regulates the solvent evaporation kinetics to ensure that the precursor solution is uniformly and slowly released in the confined space; (4) Regarding the problem of "slow diffusion and uneven spreading of the precursor solution": In this invention, the dimethyl silicone oil layer reduces the interfacial flow resistance, and the precursor solution only needs 7.05 s to complete diffusion in the 10-100 μm gap confined space; (5) Regarding the problem of "local solute depletion easily forms impurities": In this invention, the silicone oil layer regulates the solvent diffusion kinetics to ensure a continuous supply of precursor ions and avoids the formation of impurities caused by local solute depletion; (6) Regarding the problem of "poor photoelectric performance of the prepared film in the atmospheric environment": The MAPbBr3 perovskite single crystal film prepared in this invention has high crystal quality and low defect density, and the half-peak width of the fluorescence spectrum is only 18.52 nm with a steep absorption band edge, showing excellent photoelectric performance and structural stability.

[0045] Similarly, the MAPbBr3 perovskite single crystal films prepared in Examples 2 and 3 were tested. Their performance was basically similar to that of the MAPbBr3 perovskite single crystal film prepared in Example 1. They had low interface defect state density, few interface pores, and high repeatability. Moreover, the prepared MAPbBr3 perovskite single crystal film exhibited an orange square flake shape and three-dimensional semiconductor optical properties. Its fluorescence emission wavelength was at 550 nm, which is expected to be used to prepare perovskite single crystal film light-emitting diodes.

[0046] The specific effects that can be achieved by the present invention are: (1) The experimental process for preparing MAPbBr3 perovskite single crystal thin film in the present invention is simple. The ITO lower substrate with poly(9-ethylenecarbazole) layer spin-coated and the ITO upper cover plate with dimethyl silicone oil layer spin-coated are assembled to form a confined space. The precursor solution is injected through capillary action and grown in the atmospheric environment. The entire process can be completed in an atmospheric environment at room temperature, without the need for a vacuum or high-purity nitrogen environment; (2) The required chemical reagents are few in number and widely available: the main reagents include methylammonium bromide, lead bromide, polyvinylpyrrolidone, N,N-dimethylformamide, poly(9-vinylcarbazole), chlorobenzene, dimethyl silicone oil, and toluene, all of which can be purchased from various chemical reagent platforms; (3) The precursor solution diffuses quickly in confined space: in a 10-100μm gap, the precursor solution can be uniformly spread through capillary action in just 7.05s; (4) The single crystal produced by this method has high quality and high yield: the X-ray diffraction pattern shows periodic diffraction peaks of (100), (200), and (300), confirming that it is a cubic phase (Pm3m) single crystal structure with no impurity crystal signal; (5) The surface of the single crystal film synthesized by this method is smooth and dense: the scanning electron microscope image shows no pores, no cracks, and no peeling marks. Compared with the polycrystalline or rough films grown in the atmospheric environment in the prior art, the present invention achieves high-quality dense single crystal films; (6) it achieves non-destructive separation of the top cover plate and the single crystal film: thanks to the superhydrophobic and low adhesion properties of the dimethyl silicone oil layer, there are almost no crystal residues on the surface of the top cover plate after peeling, and the single crystal film is intact and undamaged, overcoming the problem of easy damage during peeling in the prior art; (7) the prepared MAPbBr3 perovskite single crystal film has excellent optical properties: the steady-state absorption spectrum shows a flat absorption plateau and steep band edge cutoff characteristics; the photoluminescence spectrum shows that the emission peak is located at 550 nm and the half-peak width is only 18.52 nm, indicating extremely low defect density and high crystal quality; (8) the prepared MAPbBr3 perovskite single crystal film is in the shape of an orange square sheet with a fluorescence emission wavelength of 550 nm, which is expected to be applied to perovskite single crystal film light-emitting diodes; (9) the method is suitable for the preparation of large-area single crystal films: the silicone oil layer of the top cover plate reduces the interfacial flow resistance and supports the rapid and uniform spreading of the precursor solution on a large-area substrate, providing a technical basis for large-scale production. (10) The MAPbBr3 perovskite single crystal thin film prepared by this method has a polarization degree of 74% for linearly polarized emission.

[0047] Furthermore, the experimental method in this invention is simple and easy to operate, requiring only a conventional spin coater and heating stage, without the need for complex equipment; the success rate of single-crystal thin films is high, and high-quality MAPbBr3 perovskite single-crystal thin films are easily formed. On the other hand, this experiment does not require nitrogen or a vacuum; it can be carried out entirely in a normal atmospheric environment (relative humidity 60%~80%, temperature 15℃~30℃), where the silicone oil layer provides a stable microenvironment isolated from water and oxygen for crystal growth. Third, this invention achieves non-destructive separation of the top cover plate and the single-crystal thin film, overcoming the problems of easy damage during peeling and easy crystal removal in existing technologies, significantly improving the yield. Fourth, the precursor solution in this invention diffuses rapidly in the confined space (only 7.05 s), spreading uniformly, ensuring the preparation of large-area continuous single-crystal thin films. Fifth, using the experimental method in this invention, MAPbBr3 perovskite single-crystal thin films with smooth and dense surfaces, free of pores and cracks, high crystal quality, and excellent optical properties can be prepared. X-ray diffraction revealed a cubic single-crystal structure with a photoluminescence spectrum of only 18.52 nm and a steep absorption band edge. Due to its excellent three-dimensional semiconductor physical properties and good environmental adaptability, this material exhibits fluorescence emission wavelengths at 550 nm, high crystal quality, low defect density, and 74% linear polarization, making it highly suitable for perovskite single-crystal thin-film light-emitting diodes and other optoelectronic devices. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing MAPbBr3 single-crystal thin films by spin-coating dimethyl silicone oil in a spatially confined environment, characterized in that, The method includes the following steps: (1) Coating the lower substrate with poly(9-ethylenecarbazole): A poly(9-ethylenecarbazole) solution is dropped onto the surface of the pretreated ITO substrate, and after spin coating, it is annealed to obtain a lower substrate coated with poly(9-ethylenecarbazole). (2) Top cover plate coated with silicone oil: Dimethyl silicone oil solution is uniformly coated on the surface of another pretreated ITO substrate, and after spin coating, annealing is performed to obtain a top cover plate coated with dimethyl silicone oil. (3) Assemble the confined space: Cover the lower substrate coated with poly(9-ethylene carbazole) with a top cover plate coated with dimethyl silicone oil, wherein the surface of the top cover plate coated with dimethyl silicone oil is in contact with the poly(9-ethylene carbazole) surface of the lower substrate. Use dovetail clips to control the distance between the top cover plate and the lower substrate to be 10-100 μm, thus forming a confined growth space between the top cover plate and the lower substrate. (4) Precursor solution injection: The MAPbBr3 precursor solution is dropped into the confined growth space and the solution is spread throughout the confined growth space by capillary action to obtain the assembled sample. (5) Atmospheric environment growth: The assembled sample is placed on a heating stage in an atmospheric environment for crystal growth until the solvent is completely evaporated; (6) Separation and post-processing: After the solvent has completely evaporated, transfer it to the glove box environment, remove the dovetail clip, let it stand for 2 to 12 hours, and then separate the top cover plate. MAPbBr3 single crystal thin film can be prepared in situ on the lower substrate.

2. The method according to claim 1, characterized in that, In step (1), the pretreatment method of the ITO substrate is as follows: the ITO substrate is ultrasonically cleaned with acetone, anhydrous ethanol, deionized water and acetone solution for 20 min each, then dried at 100 °C for 5 min, and finally placed in an ultraviolet-ozone cleaner for ozone treatment. The ITO substrate measures 14.9 × 15.1 mm. 2 ; In step (1), the spin coating speed is 4000 rpm and the time is 60 s; In step (1), the annealing temperature is 150 °C and the time is 15 min.

3. The method according to claim 1, characterized in that, In step (1), the poly(9-vinylcarbazole) solution is prepared by adding chlorobenzene to poly(9-vinylcarbazole) solid powder and stirring for at least 12 hours. The volume and mass ratio of the chlorobenzene and poly(9-ethylenecarbazole) solid powder are 2:12 and mL:mg, respectively.

4. The method according to claim 1, characterized in that, In step (2), the dimethyl silicone oil solution is prepared by adding silicone oil to toluene and stirring for at least 12 hours. The viscosity of the silicone oil at 25°C is 160±10 mPa.s, and the volume ratio of silicone oil to toluene is 50:10, μL:mL. In step (2), the spin coating speed is 4000 rpm and the time is 60 s; In step (2), the annealing temperature is 120 °C and the time is 15 min.

5. The method according to claim 1, characterized in that, In step (4), the preparation method of the MAPbBr3 perovskite precursor solution is as follows: Mix methylammonium bromide (MABr), lead bromide (PbBr2) and polyvinylpyrrolidone solid powder, add N,N-dimethylformamide solution, and stir for no less than 12h to obtain the MAPbBr3 perovskite precursor solution. The polyvinylpyrrolidone has an Mw of 1,300,000; The mass-to-volume ratio of the solid powders of methylammonium bromide (MABr), lead bromide (PbBr2), and polyvinylpyrrolidone is 93.87:294.11:5:0.5, mg:mg:mg:mL.

6. The method according to claim 1, characterized in that, In step (5), the heating rate of the heating table is 5℃ / h, the relative humidity of the environment is 60~80%, and the temperature of the environment is 15~30℃. In step (5), the crystal is allowed to stand for 12 to 72 hours to allow the solvent to evaporate naturally during growth.

7. The MAPbBr3 single crystal thin film prepared by the method according to any one of claims 1 to 6.

8. The application of the MAPbBr3 single crystal thin film of claim 8 in online polarization luminescence.

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