Preparation method of perovskite single crystal slice

Abstract

The invention provides a preparation method of a perovskite single crystal slice, which comprises the following steps of: cooling and crystallizing a perovskite precursor solution in a supersaturated state at a high temperature, taking supernate of the solution after crystals are generated, continuously concentrating to the supersaturated state, and repeating the step of cooling and crystallizing, so as to obtain the large-size perovskite single crystal slice. Manufacturing a metal oxide anode layer on the substrate layer, transferring a perovskite active layer on the metal oxide anode layer, and manufacturing a metal cathode layer on the perovskite active layer; compared with the traditional bulk single crystal, the terahertz detector of the (NH4) 3Bi2I9 single crystal slice prepared by creatively using a mechanical stripping technology of the two-dimensional single crystal slice in the perovskite material has the advantage that the response speed is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronic detection, and particularly relates to a preparation and mechanical peeling method and application of a perovskite single crystal thin sheet. Background Art

[0002] Terahertz (THz) refers to electromagnetic waves with frequencies ranging from 0.1 to 10 THz. Due to its extremely rich spectral information, strong coherence, low photon energy, strong penetrability and other characteristics, it has attracted wide attention in the fields of military, communication, search and rescue, and biological and chemical substance identification. In the early 21st century, the international community listed THz-related technologies as "the top ten technologies that will change the future world". Comparatively speaking, the research on THz technology in China started relatively late, but after nearly a decade of development, it has also made great progress. In 2020, the IMT-2030 (6G) Industry Alliance established in China clearly put forward that the integrated research on THz sensing-communication will be an important theme direction for the development of future 6G networks.

[0003] At present, the working mechanisms of new THz detectors can be divided into two categories: 1) Nonlinear photocurrent effect detection mode; 2) Photothermal effect detection mode. The former device has good sensing performance for THz electromagnetic waves, but the demanding preparation process of the sensing material makes it difficult to achieve large-scale commercialization. Comparatively speaking, THz detectors based on the photothermal effect bring new options for the commercial application of THz detection technology. The principle of photothermal detection is the process in which the detector absorbs THz radiation, generates a temperature change, and then converts the heat into an electrical signal. Some teams at home and abroad have realized the preparation of THz thermoelectric effect detectors, such as the team of Professor Fuhrer in the United States and the team of Wang Jianlu in China. Although these explorations have achieved certain success, the two-dimensional materials used have a relatively high thermal conductivity, and the device sensitivity is poor, which limits the performance of the device. The preparation cost of high-quality two-dimensional materials is still relatively expensive, and there is still a certain distance from actual application.

[0004] In recent years, perovskite materials with the structure of ABX3 have attracted wide attention due to their excellent optoelectronic properties, simple preparation process, and chemical flexibility. At the same time, the thermal conductivity and thermal diffusivity of this material are two orders of magnitude lower than those of classical semiconductors such as Si, GaAs, and CZTS. Low heat conduction and low thermal diffusivity enable the perovskite material to generate a large temperature difference when absorbing the same amount of energy (radiation), thereby realizing an obvious photothermal effect. However, perovskite materials with the ABX3 structure often exhibit a three-dimensional bulk single crystal structure, and additional cutting and polishing processes are required to realize the preparation of single crystal thin sheets, with complex processes and high costs.

[0005] By introducing trivalent B-site ion Bi 3+ to replace Pb 2+, it is possible to achieve the growth of a layered perovskite lattice of the A3B2X9 structure in which atoms within the layer are bonded by strong covalent bonds and the layers are bonded by weak van der Waals forces. Therefore, thin films or even single-layer single-crystal flakes can be obtained by means of mechanical exfoliation. At the same time, compared with three-dimensional bulk single crystals, two-dimensional perovskite flakes have a shorter carrier diffusion length and a significantly improved carrier transport ability. However, at present, there is less research on the single-crystal growth process of the A3B2X9 structure. And due to the relatively rapid and difficult-to-control crystallization process of the cooling crystallization method, most research focuses on the inverse-temperature growth method using organic solvents such as DMF. Usually, perovskite materials in the A3B2X9 structure, such as CsX, BiX3 (X = I, Br, Cl), etc., have low solubility in organic solvents, which greatly limits the development of solution growth of A3B2X9. At the same time, there is a lack of research on two-dimensional perovskite single-crystal flakes obtained by mechanical exfoliation. Therefore, it is very important to design a suitable cooling crystallization process to achieve the preparation of high-quality large-size A3B2X9 single crystals, and to design two-dimensional perovskite single-crystal flakes through a reasonable mechanical exfoliation process to realize the preparation of terahertz detection devices. Summary of the Invention

[0006] Technical Problem: The purpose of the present invention is to provide a method for preparing a perovskite single-crystal flake, a method for mechanically exfoliating the single-crystal flake, and a method for preparing a photoelectric detection device.

[0007] Technical Solution: The present invention provides a method for preparing a perovskite single-crystal flake. The preparation method includes: subjecting a perovskite precursor solution in a supersaturated state at a high temperature to cooling crystallization, taking the supernatant of the solution after crystals are generated, continuing to concentrate it to a supersaturated state, and repeating the cooling crystallization step to obtain a large-size perovskite single-crystal flake.

[0008] The precursor solution is a perovskite material dissolved in an HI aqueous solution. Among them, the perovskite material is NH4I and Bi2O3.

[0009] The concentration of the HI aqueous solution is 45 - 47 wt%, and the molar ratio of the perovskite materials NH4I and Bi2O3 is 3:1 - 3.2:1.

[0010] For the supersaturated state, its temperature is 110 - 115 °C, and the open-air placement time is 30 - 60 min.

[0011] For the cooling crystallization, the high-temperature supersaturated solution is sealed and placed in an oven at 60 - 65 °C, and the crystallization time is 20 - 30 h.

[0012] When taking the supernatant of the solution, use a PTFE filter head with a pore size of 0.22 - 0.24 μm to transfer the solution to a clean container, heat and concentrate it to a supersaturated state, and repeat the cooling crystallization step. This time, the crystallization time is 100 - 200 h.

[0013] The present invention provides a method for mechanically exfoliating perovskite single crystal flakes. After wiping the surface solution of the perovskite single crystal grown in solution, it is pasted onto the crystal surface using tape, and by continuously folding it in half and using a new tape to stick to the mother tape, the material on the tape is continuously thinned and finally transferred onto a substrate.

[0014] The tape is 3M tape or blue film tape; the number of times of folding in half is 5 - 10 times, and the substrate is an ITO or FTO transparent electrode glass substrate.

[0015] The present invention provides a method for preparing a perovskite single crystal flake optoelectronic detection device. A metal oxide anode layer is fabricated on a base layer, a perovskite active layer is transferred onto the metal oxide anode layer, and a metal cathode layer is fabricated on the perovskite active layer.

[0016] The material of the base layer is transparent glass, the material of the metal oxide anode layer is one of ITO or FTO, the perovskite active layer is (NH4)3Bi2I9, and the metal cathode layer is Au.

[0017] Advantageous effects: The advantages of the present invention are as follows:

[0018] (1) The regulation strategy of the cyclic cooling crystallization method by taking the supernatant proposed in the present invention can avoid the problem of forming more fragmented crystals and twin crystals due to the too fast crystallization rate in the cooling crystallization method. Through the process method of cyclic crystallization and taking the supernatant, the potential nucleation sites in the perovskite solution can be removed to achieve the control of the number of solution crystal seeds during the perovskite crystallization process, and high-quality perovskite single crystal flakes with large size and low defects can be prepared.

[0019] (2) The mechanical exfoliation method used in the present invention continuously thins the material on the tape by continuously folding it in half and using a new tape to stick to the mother tape. Without using the traditional cutting and polishing methods, the preparation of perovskite single crystal flakes can be realized through a simple and low-cost process, avoiding the complication of the preparation process.

[0020] (3) In the terahertz detection device prepared by the present invention, the thickness of the perovskite active layer is significantly reduced, and the detection efficiency based on the photothermal effect is increased. For the terahertz optoelectronic detection device prepared by the present invention, the on-off ratio and rise and fall times are significantly improved compared with the standard device prepared by the prior art.

[0021] (4) The present invention is simple to operate and easy to control, providing a method for the preparation of perovskite single crystals by the cooling method and the further research of two-dimensional flake optoelectronic detectors. Description of the Drawings

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings. Among them:

[0023] Figure 1 It is the X-ray diffraction pattern of the (NH4)3Bi2I9 single crystal for the cyclic cooling crystallization of the present invention;

[0024] Figure 2 It is the cross-sectional scanning electron microscope image of the (NH4)3Bi2I9 bulk single crystal prepared by the present invention;

[0025] Figure 3 It is the physical image of the (NH4)3Bi2I9 two-dimensional single crystal thin sheet prepared by the present invention;

[0026] Figure 4 It is the cross-sectional scanning electron microscope image of the (NH4)3Bi2I9 two-dimensional thin sheet prepared by the present invention;

[0027] Figure 5 It is the terahertz time-domain analysis spectrum of the (NH4)3Bi2I9 bulk single crystal prepared by the present invention;

[0028] Figure 6 It is the time-current curve of the terahertz response of the detector device of the (NH4)3Bi2I9 bulk single crystal prepared by the present invention;

[0029] Figure 7 It is the time-current curve of the terahertz response of the detector device of the (NH4)3Bi2I9 two-dimensional thin sheet prepared by the present invention. Detailed Embodiments

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will provide a detailed description of the specific embodiments of the present invention in conjunction with the embodiments of the specification.

[0031] In the present invention, the raw materials involved are all ordinary commercially available without special instructions.

[0032] The full names and abbreviations of the chemical substances involved in the present invention are shown in Table 1 as follows:

[0033] Table 1 Corresponding full names and abbreviations of chemical substances

[0034]

[0035]

[0036] Example 1

[0037] This embodiment provides a method for preparing bulk single crystals of (NH4)3Bi2I9 using a cyclic crystallization strategy.

[0038] Solution preparation

[0039] The specific steps are as follows: 4 g of NH4I and 10 g of Bi2O3 are mixed and dissolved in 50 mL of a 45 - 47 wt% HI aqueous solution, and stirred at room temperature for 3 h until the solution is clear and completely dissolved. The molar ratio of the perovskite materials NH4I and Bi2O3 is 3:1 - 3.2:1.

[0040] Crystal growth

[0041] Filter the solution, take the filtrate, and place the filtrate open - mouthed on a hot stage at 110 - 115 °C and continuously heat until suspended broken crystals appear on the surface of the solution. Then add 2 mL of HI aqueous solution, seal the container and let it stand for 2 min, and quickly transfer it to an oven at 60 - 65 °C. After 24 h, when the potential nucleation sites are basically precipitated, take out the solution from the oven, filter the solution using a 0.22 - 0.24 μm PTFE filter head, and transfer the filtrate to a clean container. Repeat the process of placing it open - mouthed on the hot stage at 110 - 115 °C until suspended broken crystals appear, add 2 mL of HI aqueous solution, seal the container and let it stand for 2 min, and quickly transfer it to an oven at 60 - 65 °C until (NH4)3Bi2I9 single crystals with a size of about 1 - 3 cm are formed.

[0042] After the single crystal preparation is completed, perform X - ray diffraction testing on it. As Figure 1 shown, the test angle range is 5° - 90°, the interval between adjacent scans is 0.02°, and the residence time at each scan point is 0.1 s. It can be seen that the measured diffraction peak distribution of (NH4)3Bi2I9 conforms to the XRD distribution in the literature.

[0043] In addition, perform scanning electron microscope characterization on the cross - section of the bulk single crystal of (NH4)3Bi2I9. As Figure 2 shown, it can be seen that there is an obvious layered arrangement at the cross - section, which proves the feasibility of preparing two - dimensional single crystal flakes by mechanical exfoliation of the (NH4)3Bi2I9 bulk single crystal.

[0044] Example 2

[0045] Based on Example 1, this embodiment provides a method for preparing two - dimensional single crystal flakes of (NH4)3Bi2I9 using a mechanical exfoliation method.

[0046] Place the (NH4)3Bi2I9 bulk single crystal prepared in Example 1 on a blue film tape or 3M tape. By continuously folding it in half and using a new tape to stick to the mother tape, repeat folding in half about 10 times, and single crystal flakes of (NH4)3Bi2I9 can be obtained on the tape. The physical picture is as Figure 3 shown. Stick the tape on the ITO glass and soak it in toluene. After 30 minutes, take out the single crystal flakes from toluene and wait for the toluene on the surface to volatilize naturally, then the single crystal flakes are successfully transferred to the ITO glass.

[0047] After the two-dimensional single crystal flakes are prepared, characterize the cross-section of the single crystal flakes by scanning electron microscopy, as Figure 4 shown. It can be seen that the thickness of the single crystal flakes is about 10 μm.

[0048] Example 3

[0049] Based on Example 2, this example prepares a terahertz photodetector of (NH4)3Bi2I9 two-dimensional single crystal flakes.

[0050] First, characterize whether the (NH4)3Bi2I9 material itself absorbs terahertz light through terahertz time-domain analysis spectroscopy, as Figure 5 shown. It can be found that this perovskite material has a relatively obvious absorption in the terahertz band. Then, by means of vacuum coating, evaporate Au metal electrodes on the (NH4)3Bi2I9 single crystal flakes to prepare a vertical structure photodetector of ITO / (NH4)3Bi2I9 single crystal flakes / Au, and test its time-current curve of terahertz response at a terahertz wavelength of 0.1 THz, as Figure 6 shown.

[0051] Example 4

[0052] To verify the beneficial effects of the present invention, this example provides a terahertz photodetector of (NH4)3Bi2I9 bulk single crystal. Conduct a comparative test with the detection device prepared in Example 3 of the present invention, and compare the test results by means of scientific demonstration to verify the real effects of this method.

[0053] The difference between this example and Example 3 is that:

[0054] This example does not use the mechanical exfoliation process. Directly evaporate Au electrodes on both sides of the (NH4)3Bi2I9 prepared by the solution method, and test its time-current curve of terahertz response at a terahertz wavelength of 0.1 THz, as Figure 7 shown.

[0055] The remaining steps and preparation processes are the same as those in Example 1.

[0056] The prepared photovoltaic device was compared with the photovoltaic device prepared in Example 1, and the results are shown in Table 1.

[0057] Table 1 Comparison of terahertz responses of bulk single crystals and two-dimensional thin single crystal devices

[0058]

[0059] As can be seen from Table 1, for the same (NH4)3Bi2I9 single crystal, the terahertz detection performance of the two-dimensional single crystal thin film is significantly improved compared to the bulk single crystal.

[0060] In summary, the optimized cyclic crystallization cooling growth method proposed in the present invention promotes the precipitation of potential nucleation sites in the solution through cyclic crystallization, achieving the reduction of the nucleation site density in the solution, slowing down the solution cooling crystallization rate, and realizing the preparation of large-sized (NH4)3Bi2I9 bulk single crystals. At the same time, the present invention innovatively uses the mechanical exfoliation technology of two-dimensional single crystal thin flakes in perovskite materials. The terahertz detector prepared from the (NH4)3Bi2I9 single crystal thin flakes has a significantly improved response speed compared to traditional bulk single crystals.

[0061] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A method for preparing a perovskite single crystal thin sheet, characterized in that: The preparation method includes: cooling and crystallizing the perovskite precursor solution in a supersaturated state at a high temperature, taking the supernatant of the solution after crystals are formed, continuing to concentrate it to a supersaturated state, and repeating the cooling and crystallization steps to obtain large-size perovskite single-crystal flakes.

2. The method for preparing a perovskite single crystal thin sheet according to claim 1, wherein: The precursor solution is a perovskite material dissolved in an HI aqueous solution, where the perovskite material is NH4I and Bi2O3.

3. The method for preparing a perovskite single crystal thin sheet according to claim 2, characterized in that: The concentration of the HI aqueous solution is 45-47 wt%, and the molar ratio of the perovskite materials NH4I and Bi2O3 is 3:1-3.2:

1.

4. The preparation method of the perovskite single crystal thin sheet according to claim 1, characterized in that: For the supersaturated state, the temperature is 110-115 °C, and the open placement time is 30-60 min.

5. The preparation method of the perovskite single crystal thin sheet according to claim 1, wherein: For the cooling and crystallization, the high-temperature supersaturated solution is sealed and placed in an oven at 60-65 °C, and the crystallization time is 20-30 h.

6. The method for preparing a perovskite single crystal thin sheet according to claim 1 or 5, characterized in that: For taking the supernatant of the solution, a PTFE filter head with a pore size of 0.22-0.24 μm is used to transfer the solution to a clean container, heat and concentrate it to a supersaturated state, and repeat the cooling and crystallization steps. This time, the crystallization time is 100-200 h.

7. A mechanical exfoliation method for a perovskite single crystal thin sheet prepared by the method according to claim 1, characterized in that: The mechanical peeling method of the perovskite single-crystal flake is: wipe the surface solution of the perovskite single crystal grown in the solution, stick the tape to the crystal surface, and continuously fold it and use a new tape to stick to the mother tape to continuously thin the material on the tape and finally transfer it to the substrate.

8. The mechanical exfoliation method of the perovskite single crystal thin sheet according to claim 7, characterized in that: The tape is 3M tape or blue film tape; the number of folding times is 5-10 times, and the substrate is an ITO or FTO transparent electrode glass substrate.

9. A method for preparing a perovskite single crystal thin film for a photodetector by using the method according to any one of claims 1-7, characterized in that: A metal oxide anode layer is fabricated on the base layer, a perovskite active layer is transferred on the metal oxide anode layer, and a metal cathode layer is fabricated on the perovskite active layer.

10. The method for preparing a photoelectric detection device according to claim 9, wherein: The material of the base layer is transparent glass, the material of the metal oxide anode layer is one of ITO or FTO, the perovskite active layer is (NH4)3Bi2I9, and the metal cathode layer is Au.

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