A structure regulation method of a two-dimensional bismuth-based perovskite material based on CVD growth

Abstract

This invention discloses a method for structural control of two-dimensional bismuth-based perovskite materials grown by CVD. By precisely controlling the mass transfer process of the precursor, single-crystal bismuth-based perovskite materials with a thickness ≤10nm and a lateral dimension ≥500μm are obtained, solving the problems of small single-crystal size and uncontrollable thickness of two-dimensional bismuth-based perovskite materials prepared by existing methods. The method includes the following steps: placing two precursor materials in two temperature zones of a dual-temperature zone tube furnace, using a mica substrate, introducing argon and hydrogen into the tube furnace, and heating the two temperature zones of the tube furnace to predetermined temperatures to allow the reaction to proceed, thereby obtaining large-size two-dimensional bismuth-based perovskite materials. The preparation process involved in this invention is simple, convenient to operate, and has good repeatability. By changing the temperature and carrier gas flow rate of the two temperature zones of the tube furnace, the thickness and morphology of the two-dimensional bismuth-based perovskite material can be controlled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of CVD growth of two-dimensional materials, and particularly relates to a structure regulation method of two-dimensional bismuth-based perovskite material based on CVD growth. BACKGROUND

[0002] Halide perovskite material is a new type of optoelectronic material, which has the characteristics of easy doping modification, simple preparation process, adjustable band gap (1.2-2.8 eV), excellent light absorption efficiency (~10 5 cm -1 ), high photoelectric conversion efficiency (~25.2%) and large diffusion length, which is superior to traditional two-dimensional materials, which makes the perovskite material achieve excellent performance in the field of optoelectronics, and has a broad application prospect in the fields of optoelectronic transistors, light-emitting diodes (LEDs) and lasers.

[0003] At present, the research on halide hybrid perovskite is focused on lead-based perovskite material, but the lead-based perovskite material is extremely unstable, and the product after decomposition will enter the soil or water with rainwater, which has great toxicity to animals and plants in the environment and human body, resulting in great challenges in economic cost, sustainability and environmental safety of lead-based perovskite material, which eliminates the possibility of large-scale commercial application, therefore, it is of great significance to develop lead-free hybrid perovskite material. Researchers have developed non-toxic or low-toxic metal elements Sn, Bi and Sb to replace Pb, among which bismuth-based perovskite material has higher stability and better potential performance. It has a stable Bi 3+ , and has the same electronic structure (both have 6s 2+ electron pairs) and similar ionic radius as Pb 2 , and is considered as a green perovskite material with great development potential. Therefore, it is of great scientific significance and broad application prospect to study the growth technology of large-size two-dimensional bismuth-based perovskite CVD.

[0004] In the prior art, the methods for preparing two-dimensional bismuth-based perovskites mainly include a liquid phase method and a confinement method. The liquid phase method needs to first dissolve a precursor in a good polar solvent, such as dimethyl sulfoxide (DMSO) or dimethylformamide (DMF), and then drop a proper amount of the solution into a poor solvent (such as n-hexane or toluene), so as to initiate the nucleation and growth of perovskite nanocrystals. It is mentioned in the paper "Research on Design, Structure Regulation and Photocatalytic Degradation of Tetracycline Performance of Bismuth-based Perovskite" (Li Danqing, Shaanxi University of Science and Technology) that a molten salt method, a sol-gel method and a hydrothermal method are used to synthesize bismuth-based perovskites, and the molten salt method, the sol-gel method and the hydrothermal method all belong to the liquid phase method. CN111285797A discloses a solvent-thermal method for preparing a bismuth-based perovskite material, and the solvent-thermal method also belongs to the liquid phase method. Although the method can be carried out in air and the synthesis device is simple, only nanocrystals with a size less than 1 μm can be obtained. The confinement method needs to artificially create a space with a height less than 100 nm, so that the crystal grows in the limited space, and a bismuth-based perovskite material with a specific thickness can be obtained. The transverse size of the limited space in the method is usually small, and the thickness distribution is extremely uneven, which is not suitable for large-scale production.

[0005] It is mentioned in the paper "Preparation and Performance Research of Perovskite Resistive Random Access Memory with Different Dimensions" (Lin Jiaguang, Shaanxi University of Science and Technology) that a three-dimensional perovskite material is prepared by using a gas deposition method, but a single-temperature zone tube furnace is used, and the precursor is heated by preheating, so that the temperature fluctuation is large and accurate control cannot be achieved. It is mentioned in the paper "Research on Growth and Heterojunction Luminescence Characteristics of Two-dimensional TMDCs by DE CVD" (Zhang Wenyang, Chongqing University of Technology) that the type of substrate is changed and the size of two-dimensional material RMDCs is increased. Specifically, a larger size of TMDCs (MX2) is prepared on the surface of SiO2 by using a gas deposition method, but the size still has room for further improvement. Studies have shown that the type of substrate MX2 has a great influence on the size, growth time and quality. For example, mica with an atomic level flatness surface is often used to epitaxially grow MX2, but the atomic migration on the surface of mica is difficult, which is not conducive to the preparation of MX2 in a large range and a large area. It can be seen that in the prior art, mica is not suitable as a substrate for preparing large-size materials by using a gas deposition method.

[0006] In recent years, chemical vapor deposition (CVD) method is widely used in the preparation of various two-dimensional materials, such as molybdenum sulfide, graphene and boron nitride. But most of them are limited to binary compounds, and few reports use CVD method to grow ternary two-dimensional materials with a thickness of less than 10 nanometers and a lateral single crystal size of more than 200 microns. The reasons are as follows: 1. The preparation of ternary two-dimensional materials often uses multiple precursors. Different types of precursors have different diffusion processes on the substrate surface. It is necessary to match the types of multiple precursors so that they can effectively diffuse on the substrate surface to obtain large-size ternary two-dimensional materials. 2. If the product obtained has a specific stoichiometric ratio, the proportion of the volatilized precursor needs to be consistent with the stoichiometric ratio, and the complete reaction of the precursor needs to be ensured, so that pure phase product can be produced. If complete reaction cannot be ensured, the precursor will directly form a binary two-dimensional material on the substrate surface. 3. If large-size ternary single-crystal two-dimensional materials with controllable thickness are to be obtained, the physical and chemical properties of the precursor and the obtained product, the reaction diffusion rate and the reaction kinetics process need to be mastered. Under the condition that the obtained product is a pure phase material, the reaction chamber structure, the precursor distance, the precursor quality, the carrier gas flow, the reaction substrate distance, the heating step and the substrate type are optimized to ensure that the precursor can stably grow into a two-dimensional structure on the substrate. It cannot be obtained by limited variable attempts. The secret base two-dimensional material in the present application belongs to the all-inorganic perovskite system in ternary two-dimensional materials, and has excellent photoluminescence characteristics.

[0007] Therefore, it has important scientific significance and broad application prospect to study the structure regulation method of large-size two-dimensional bismuth-based perovskite material based on CVD growth. SUMMARY

[0008] In view of the above prior art, the purpose of the present application is to provide a structure regulation method of two-dimensional bismuth-based perovskite material based on CVD growth. The method of chemical vapor deposition (CVD) is used to precisely control the mass transfer behavior of two solid precursors in a double-temperature-zone tube furnace. Large-size two-dimensional bismuth-based perovskite material with controllable thickness is obtained on mica substrate by CVD method. The method has good repeatability, and plays an important role in the preparation and research of two-dimensional bismuth-based perovskite.

[0009] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0010] The first aspect of the present application provides a structure regulation method of two-dimensional bismuth-based perovskite material based on CVD growth, which comprises the following steps:

[0011] (1) Put the first precursor and the second precursor in temperature zone I and temperature zone II in the tube furnace respectively, and put the mica substrate in the downstream area of the second precursor. Argon and hydrogen are introduced, and the air in the tube furnace is exhausted;

[0012] (2) After the air in the tube furnace is purged, the tube furnace is heated and the flow rates of argon and hydrogen are adjusted to transport the first and second precursors to the substrate surface for reaction, thus obtaining the two-dimensional bismuth-based perovskite material.

[0013] Preferably, the first precursor is BiI3, and the second precursor is one of KI, CsI, or RbI.

[0014] Preferably, in step (1), the mass ratio of the first precursor to the second precursor is (0.1-1.0):(0.5-3.0).

[0015] In step (1), the volatilization temperature of the first precursor is lower than that of the second precursor. The volatilization temperature of the second precursor is similar to that of the deposition temperature of the two-dimensional bismuth-based perovskite material. Therefore, the first precursor is placed in the upstream temperature zone I of the dual-temperature tube furnace, and the second precursor and the substrate are placed in the downstream temperature zone II.

[0016] Preferably, in step (1), the mica substrate is a freshly peeled fluorine-gold mica substrate.

[0017] Fluorophyllite is a layered material with a surface roughness of less than 0.1 nm, which is much smaller than the surface roughness of existing substrate materials such as SiO2 / Si substrates, soda-lime glass substrates, and sapphire substrates. In addition, freshly peeled fluorophyllite substrates have no dangling bonds on the substrate surface, which is conducive to the diffusion of precursor molecules on the substrate surface, thereby reducing the nucleation density and increasing the grain size.

[0018] Preferably, in step (1), the first precursor is located at the center of the tubular furnace temperature zone I, and the second precursor is located at the center of the tubular furnace temperature zone II.

[0019] Preferably, the distance between the mica substrate and the second precursor is 5-30 mm.

[0020] Preferably, the temperature of zone I in the tubular furnace is 250-350℃, and the temperature of zone II is 370-500℃.

[0021] The temperature range of zone II in the tube furnace is conducive to the growth of large-sized two-dimensional bismuth-based perovskite single crystals with a thickness of ≤10nm. Specifically, when the growth temperature is higher than the upper limit of zone II, the desorption phenomenon on the substrate surface is intensified, which will cause the thickness of the grown two-dimensional bismuth-based perovskite single crystal to increase. When the growth temperature is lower than the lower limit of zone I, the second precursor is not easy to volatilize, while the first precursor can volatilize. Therefore, the final product will be bismuth iodide crystal, rather than two-dimensional bismuth-based perovskite single crystal.

[0022] Preferably, in step (1), the flow rate of argon is 10-30 sccm and the flow rate of hydrogen is 5-15 sccm.

[0023] Preferably, in step (2), the flow rate of argon is 100-300 sccm and the flow rate of hydrogen is 20-50 sccm.

[0024] In step (2), argon is used as a diluent gas and hydrogen is used as a reducing gas.

[0025] Before the two temperature zones of the tube furnace reach their designated temperatures, the flow rates of argon and hydrogen are kept low. This serves to purge the air from the furnace and prevent the precursor from being prematurely transported to the substrate surface, which could lead to premature nucleation and uncontrollable final nucleation density. Once the tube furnace reaches its designated temperature, the flow rates of argon and hydrogen are increased. This allows the precursor to be transported to the substrate surface along with the carrier gas, where it reacts and deposits to form a two-dimensional bismuth-based perovskite material.

[0026] Preferably, in step (2), after the reaction is completed, the heating of the tubular furnace is immediately turned off, and the furnace body is slid away from the precursor to prevent residual heat from causing the precursor to volatilize.

[0027] Preferably, in step (2), the reaction time is 60-240 min.

[0028] In a second aspect, the present invention provides a two-dimensional bismuth-based perovskite material, wherein the chemical formula of the two-dimensional bismuth-based perovskite material is X3Bi2I9 (X = K, Cs or Rb).

[0029] Preferably, when the morphology of the obtained two-dimensional bismuth-based perovskite material is planar, its size is 100-1000 μm and its thickness is 5-50 nm; when the morphology of the obtained two-dimensional bismuth-based perovskite material is nanowire-shaped, its length is 200-2000 μm, its width is 2-10 μm and its height is 50-100 nm.

[0030] The morphology of the two-dimensional bismuth-based perovskite material is related to the mass of the first and second precursors, the temperature of zone I and zone II of the tube furnace, and the carrier gas flow rate. By adjusting the mass of the first and second precursors, the temperature of zone I and zone II of the tube furnace, and the carrier gas flow rate, the mass transfer process of the precursors can be changed, thereby obtaining two-dimensional bismuth-based perovskite materials with different morphologies.

[0031] The beneficial effects of this invention are:

[0032] This invention employs two solid sources as precursors, controlling their volatilization behavior at two independent temperatures. This allows for precise control of the mass transfer behavior of the precursors on the substrate surface. Combined with a special heating process, the nucleation density of the target product is significantly reduced. After long-term stable growth, a large-size two-dimensional bismuth-based perovskite is finally obtained on a mica substrate. When the morphology of the obtained two-dimensional bismuth-based perovskite material is planar, its size is 100-1000 μm and its thickness is 5-50 nm. When the morphology of the obtained two-dimensional bismuth-based perovskite material is nanowire-shaped, its length is 200-2000 μm, its width is 2-10 μm, and its height is 50-100 nm. Attached Figure Description

[0033] Figure 1 Optical images of the product obtained in Example 1 of this invention ( Figure 1 a) and XRD test results ( Figure 1 b)

[0034] Figure 2 AFM image of the product obtained in Example 1 of this invention ( Figure 2 a) and XPS test results ( Figure 2 b- Figure 2 d);

[0035] Figure 3 The optical properties of the product obtained in Example 2 of this invention Figure 3 a) and AFM images ( Figure 3 b and Figure 3 c)

[0036] Figure 4 Optical images of the product obtained in Example 3 of this invention;

[0037] Figure 5 Optical images of the product obtained in Example 4 of this invention;

[0038] Figure 6 : Schematic diagram of the reaction apparatus of the present invention. Detailed Implementation

[0039] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0040] As described in the background section, existing methods for synthesizing bismuth-based perovskite materials mainly include liquid-phase methods and confinement methods. While the liquid-phase method can be carried out in air and has a simple synthesis apparatus, it can only produce nanocrystals with a size of less than 1 μm. The bismuth-based perovskite materials prepared by the confinement method have small lateral dimensions and extremely uneven thickness distribution, making them unsuitable for large-scale production.

[0041] Based on this, the present invention provides a method for structural control of two-dimensional bismuth-based perovskite materials grown by CVD, comprising the following steps:

[0042] (1) Under normal pressure, place 0.1-1.0g of the first precursor BiI3 powder in the center of temperature zone I of the dual-temperature tube furnace, and place 0.5-3.0g of the second precursor XI (X=K, Cs or Rb) powder in the center of temperature zone II of the dual-temperature tube furnace. Place the fluorophlogopite substrate as a substrate downstream of the second precursor at a distance of 5-30mm from the second precursor. Introduce argon and hydrogen gas with a flow rate of 10-30sccm and a flow rate of 5-15sccm to purge the air in the dual-temperature tube furnace.

[0043] (3) After the air in the dual-temperature tube furnace is exhausted, heat the dual-temperature tube furnace to make the temperature of temperature zone I reach 250-350℃ and the temperature of temperature zone II reach 370-500℃. Adjust the argon flow rate to 100-300 sccm and the hydrogen flow rate to 20-50 sccm so that the first and second precursors can volatilize and be transported to the surface of the fluorine-phlogopite substrate for reaction for 60-240 min. After the reaction is completed, immediately turn off the heating of the dual-temperature tube furnace and slide the furnace body away from the precursor to prevent the residual heat from volatilizing the precursor, thus obtaining a large-size two-dimensional bismuth-based perovskite material.

[0044] The chemical formula of the two-dimensional bismuth-based perovskite material is X3Bi2I9 (X = K, Cs, or Rb). If its morphology is planar, its single crystal size is 100-1000 μm and its thickness is 5-50 nm. If its morphology is nanowire-shaped, its length is 200-2000 μm, its width is 2-10 μm, and its height is 50-100 nm.

[0045] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be described in detail below with reference to specific embodiments.

[0046] The test materials used in the embodiments of this invention are all conventional test materials in the art and can be purchased through commercial channels.

[0047] In this invention, the dual-temperature tube furnace is model SK-G05123K-2-420-HS.

[0048] Example 1: Preparation of two-dimensional bismuth-based perovskite materials

[0049] (1) Under normal pressure, place 0.1g of the first precursor BiI3 powder in the center of temperature zone I of the dual-temperature tube furnace, place 0.5g of the second precursor CsI powder in the center of temperature zone II, place the fluorinated phlogopite substrate downstream of CsI, 5mm away from CsI, and introduce argon and hydrogen into the dual-temperature tube furnace. The flow rate of argon is 30sccm and the flow rate of hydrogen is 15sccm to purge the oxygen in the dual-temperature tube furnace.

[0050] (2) After the oxygen in the dual-temperature tube furnace is purged, the temperature of the dual-temperature tube furnace is increased to 250°C in temperature zone I and 370°C in temperature zone II. The argon flow rate is adjusted to 100 sccm and the hydrogen flow rate is adjusted to 20 sccm. The first precursor BiI3 powder and the second precursor CsI powder are volatilized to react on the surface of the fluorinated phlogopite substrate for 240 min. After the reaction is completed, the heating of the dual-temperature tube furnace is immediately turned off and the furnace body is slid away from the precursor to prevent the residual heat from continuing to volatilize the precursor, thus obtaining the two-dimensional bismuth-based perovskite material.

[0051] Figure 1 a is an optical image of the two-dimensional bismuth-based perovskite material obtained in this embodiment. Figure 1 As can be seen from a, it is dart-shaped with a diameter of 1000μm. Figure 1 b represents the XRD test results of the two-dimensional bismuth-based perovskite material prepared in this embodiment. Figure 1 The three peaks 101, 202, and 404 in b indicate that the product is Cs3Bi2I9 and that the product has a consistent out-of-plane orientation.

[0052] Figure 2 a is the AFM image of the two-dimensional bismuth-based perovskite material prepared in this embodiment. Figure 2 As can be seen, the thickness of the obtained two-dimensional bismuth-based perovskite material with the chemical formula Cs3Bi2I9 is ​​only 7 nm. Figure 2 b- Figure 2 d represents the XPS test result of the two-dimensional bismuth-based perovskite material prepared in this embodiment, derived from... Figure 2 b- Figure 2 The curve d yields the molar ratios of elements in the two-dimensional bismuth-based perovskite material: Cs:Bi:I = 3.14:1.92:9.78. Figure 1 The XRD results are consistent.

[0053] Example 2: Preparation of two-dimensional bismuth-based perovskite materials

[0054] (1) Under normal pressure, place 0.2g of the first precursor BiI3 powder in the center of temperature zone I of the dual-temperature tube furnace, place 0.8g of the second precursor CsI powder in the center of temperature zone II, place the fluorinated phlogopite substrate downstream of CsI, 10mm away from CsI, and introduce argon and hydrogen into the dual-temperature tube furnace. The flow rate of argon is 20sccm and the flow rate of hydrogen is 10sccm to purge the oxygen in the tube furnace.

[0055] (2) After the oxygen in the dual-temperature tube furnace is purged, the temperature of the dual-temperature tube furnace is increased to 280°C in temperature zone I and 450°C in temperature zone II. The argon flow rate is adjusted to 200 sccm and the hydrogen flow rate is adjusted to 50 sccm. The first precursor BiI3 powder and the second precursor CsI powder are volatilized to react on the surface of the fluorinated phlogopite substrate for 200 min. After the reaction is completed, the heating of the dual-temperature tube furnace is immediately turned off and the furnace body is slid away from the precursor to prevent the residual heat from continuing to volatilize the precursor, thus obtaining the two-dimensional bismuth-based perovskite material.

[0056] Figure 3 a is an optical image of the two-dimensional bismuth-based perovskite material obtained in this embodiment. Figure 3 As can be seen, the obtained two-dimensional bismuth-based perovskite material exhibits a nanowire-like structure with a length of up to 2000 μm. Figure 3 b and Figure 3 c is the AFM image of the two-dimensional bismuth-based perovskite material prepared in this embodiment. Figure 3 b and Figure 3 As can be seen from c, the width of the obtained nanowire-shaped two-dimensional bismuth-based perovskite material is 2 μm and the height is 92 nm.

[0057] Example 3: Preparation of two-dimensional bismuth-based perovskite materials

[0058] (1) Under normal pressure, the precursors were prepared with two ratios of BiI3:CsI = 0.1g:0.5g and 0.55g:0.5g. The BiI3 powder was placed in the center of temperature zone I of the dual-temperature tube furnace, and the CsI powder was placed in the center of temperature zone II. The fluorinated mica substrate was placed downstream of CsI and 15 mm away from CsI. Argon and hydrogen were introduced into the dual-temperature tube furnace at a flow rate of 15 sccm and a flow rate of 8 sccm to purge the oxygen in the dual-temperature tube furnace.

[0059] (2) After the oxygen in the dual-temperature tube furnace is purged, the temperature of the dual-temperature tube furnace is increased to 400°C in temperature zone I and 400°C in temperature zone II. The argon flow rate is adjusted to 300 sccm and the hydrogen flow rate is adjusted to 40 sccm. The first precursor BiI3 powder and the second precursor CsI powder are volatilized to react on the surface of the fluorinated phlogopite substrate for 60 min. After the reaction is completed, the heating of the dual-temperature tube furnace is immediately turned off and the furnace body is slid away from the precursor to prevent the residual heat from continuing to volatilize the precursor, thus obtaining the two-dimensional bismuth-based perovskite material.

[0060] Figure 4 This is an optical image of the two-dimensional bismuth-based perovskite material obtained in this embodiment. Figure 4 Two-dimensional bismuth-based perovskite materials were prepared when the ratio of the first precursor BiI3 to the second precursor CsI was 0.1 g to 0.5 g. As can be seen from the figure, the two-dimensional bismuth-based perovskite materials exhibit a dart-shaped appearance. Figure 4 Two-dimensional bismuth-based perovskite material was prepared by mixing the first precursor BiI3 with the second precursor CsI at a ratio of 0.55g. As can be seen from the figure, the two-dimensional bismuth-based perovskite material presents an equilateral triangle shape.

[0061] As can be seen from this embodiment, the structure of two-dimensional bismuth-based perovskite materials can be controlled by changing the mass ratio of the first precursor and the second precursor.

[0062] Example 4: Preparation of two-dimensional bismuth-based perovskite materials

[0063] (1) Under normal pressure, place 0.8g of the first precursor BiI3 powder in the center of temperature zone I of the dual-temperature tube furnace, place 2.0g of the second precursor CsI powder in the center of temperature zone II, place the fluorinated phlogopite substrate downstream of CsI at a distance of 20mm from CsI, and introduce argon and hydrogen into the dual-temperature tube furnace. The flow rate of argon is 15sccm and the flow rate of hydrogen is 8sccm to purge the oxygen in the dual-temperature tube furnace.

[0064] (2) After the oxygen in the dual-temperature tube furnace is purged, the temperature of the dual-temperature tube furnace is increased to 350°C in temperature zone I and 500°C in temperature zone II. The argon flow rate is adjusted to 250 sccm and the hydrogen flow rate is adjusted to 25 sccm. The first precursor BiI3 powder and the second precursor CsI powder are volatilized to react on the surface of the fluorinated phlogopite substrate for 80 min. After the reaction is completed, the heating of the dual-temperature tube furnace is immediately turned off and the furnace body is slid away from the precursor to prevent the residual heat from continuing to volatilize the precursor, thus obtaining the two-dimensional bismuth-based perovskite material.

[0065] Example 5: Preparation of two-dimensional bismuth-based perovskite materials

[0066] 1) Under normal pressure, place 1.0g of the first precursor BiI3 powder in the center of temperature zone I of the dual-temperature tube furnace, place 3.0g of the second precursor CsI powder in the center of temperature zone II, place the fluorinated phlogopite substrate downstream of CsI at a distance of 30mm from CsI, and introduce argon and hydrogen into the dual-temperature tube furnace at a flow rate of 10sccm and a flow rate of 5sccm to purge the oxygen from the dual-temperature tube furnace.

[0067] (2) After the oxygen in the dual-temperature tube furnace is purged, the temperature of the dual-temperature tube furnace is increased to 350°C in temperature zone I and 500°C in temperature zone II. The argon flow rate is adjusted to 250 sccm and the hydrogen flow rate is adjusted to 25 sccm. The first precursor BiI3 powder and the second precursor CsI powder are volatilized onto the surface of the fluorinated phlogopite substrate and reacted for 60 min. After the reaction is completed, the heating of the dual-temperature tube furnace is immediately turned off and the furnace body is slid away from the precursor to prevent the residual heat from continuing to volatilize the precursor, thus obtaining the two-dimensional bismuth-based perovskite material.

[0068] Comparative Example 1: Preparation of two-dimensional bismuth-based perovskite materials using SiO2 / Si substrate as a substrate

[0069] (1) Under normal pressure, place 0.1g of the first precursor BiI3 powder in the center of temperature zone I of the dual-temperature tube furnace, place 0.5g of the second precursor CsI powder in the center of temperature zone II, place the mica substrate downstream of CsI, 5mm away from CsI, and introduce argon and hydrogen into the dual-temperature tube furnace. The flow rate of argon is 30sccm and the flow rate of hydrogen is 15sccm to purge the oxygen in the dual-temperature tube furnace.

[0070] (2) After the oxygen in the dual-temperature tube furnace is purged, the temperature of the dual-temperature tube furnace is increased to 250°C in temperature zone I and 370°C in temperature zone II. The argon flow rate is adjusted to 100 sccm and the hydrogen flow rate is adjusted to 20 sccm. The first precursor BiI3 powder and the second precursor CsI powder are volatilized to the surface of the mica substrate and reacted for 240 min. After the reaction is completed, the heating of the dual-temperature tube furnace is immediately turned off and the furnace body is slid away from the precursor to prevent the residual heat from continuing to volatilize the precursor, thus obtaining the two-dimensional bismuth-based perovskite material.

[0071] Figure 5 Optical images of the two-dimensional bismuth-based perovskite material prepared for this comparative example are shown. Figure 5 As can be seen, the two-dimensional bismuth-based perovskite material exhibits a nanowire shape with a length of approximately 300 μm, and the nanowires have a deep contrast and considerable thickness. This is because the SiO2 / Si substrate surface has numerous dangling bonds and trenches, which hinder the diffusion of precursor molecules.

[0072] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for controlling the structure of two-dimensional bismuth-based perovskite materials grown by CVD, characterized in that, Includes the following steps: (1) Place the first precursor and the second precursor in temperature zone I and temperature zone II of the tube furnace respectively, place the mica substrate in the downstream region of the second precursor, and introduce argon and hydrogen to purge the air in the tube furnace. Wherein, the first precursor is BiI3, and the second precursor is one of KI, CsI or RbI; the flow rate of argon is 10-30 sccm, and the flow rate of hydrogen is 5-15 sccm; the first precursor is located in the center of the tube furnace temperature zone I, the second precursor is located in the center of the tube furnace temperature zone II, and the distance between the mica substrate and the second precursor is 5-30 mm. (2) After the air in the tube furnace is exhausted, heat the tube furnace so that the temperature of zone I in the tube furnace is 250-350℃ and the temperature of zone II is 370-500℃. Adjust the argon flow rate to 100-300 sccm and the hydrogen flow rate to 20-50 sccm. Transport the first precursor and the second precursor to the surface of the mica substrate for reaction. After the reaction is completed, immediately turn off the heating of the tube furnace and slide the furnace body to a position away from the precursor to prevent the residual heat from causing the precursor to volatilize, and obtain two-dimensional bismuth-based perovskite material. When the morphology of two-dimensional bismuth-based perovskite materials is planar, their size is 100-1000 μm and their thickness is 5-50 nm; when the morphology of two-dimensional bismuth-based perovskite materials is nanowire-like, their length is 200-2000 μm, their width is 2-10 μm, and their height is 50-100 nm.

2. The method for structural control of two-dimensional bismuth-based perovskite materials as described in claim 1, characterized in that, In step (1), the mass ratio of the first precursor to the second precursor is (0.1-1.0):(0.5-3.0).

3. The method for structural control of two-dimensional bismuth-based perovskite materials as described in claim 1, characterized in that, In step (1), the mica substrate is a fluorinated gold mica substrate.

4. The method for structural control of two-dimensional bismuth-based perovskite materials as described in claim 1, characterized in that, In step (2), the reaction time is 60-240 min.

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