Preparation method and application of pure-phase two-dimensional halogen perovskite epitaxial homogeneous / heterojunction material

Abstract

The invention discloses a preparation method and application of a pure-phase two-dimensional halogen perovskite epitaxial homogeneous / heterojunction material. The method comprises the following steps: 1) synthesizing a two-dimensional lead-based or tin-based halide perovskite bulk crystal; 2) screening out single crystals from the blocky crystals obtained in the step 1), mechanically stripping and transferring the single crystals to a substrate, and purifying to remove a 3D phase; and 3) preparing an epitaxial growth solution, dripping chlorobenzene and the epitaxial growth solution on the substrate obtained in the step 2) at the same time for epitaxial growth to obtain an epitaxial heterojunction or homojunction material with a pure-phase epitaxial domain, or dripping chlorobenzene and the epitaxial growth solution at the same time on the prepared epitaxial heterojunction material for epitaxial growth to realize preparation of a multi-domain heterostructure. The method is used under different n values, epitaxial heterojunctions and ultra-narrow epitaxial heterojunctions with large lattice mismatch can be constructed, and epitaxial superlattices with high periods can be synthesized; and a high-quality photoelectric device can be obtained in combination with a Van der Waals transfer technology, and the method has an extremely high application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of two-dimensional halogen perovskite materials, and relates to a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material, a preparation method and application thereof. Background Art

[0002] Existing studies have shown that in-plane epitaxial two-dimensional heterojunctions have good structural controllability, flexible integration, precise chemical and electronic structure, high carrier mobility, etc., which makes it have broad prospects for the development of electronics, and it is also a material platform for discovering novel physical phenomena. However, there are currently a series of important challenges in the two-dimensional halogen perovskite epitaxial heterojunction, such as: First, there is a lack of reliable and universal methods to synthesize epitaxial heterojunctions with high purity two-dimensional halogen perovskites. Second, when the lattice mismatch of the two materials is >5%, the interface is usually difficult to maintain, making the epitaxial domain a polycrystalline material, so there is a lack of reliable methods to synthesize highly lattice-mismatched epitaxial heterojunctions. Third, there is no reliable method to achieve epitaxial superlattices with well-defined chemical structures and multi-heterojunctions with ultra-narrow epitaxial domains (width less than 50nm). Fourth, there is a lack of effective methods to realize electronic devices of in-plane two-dimensional halogen perovskite epitaxial single crystal heterojunctions.

[0003] Based on this, the present invention provides a method for preparing high-quality two-dimensional halogen perovskite materials that can obtain high phase purity epitaxial single crystal materials. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies in the prior art and provide a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material and a preparation method thereof. The method can not only produce a heterojunction, but can also be used for homojunction preparation, and can obtain a high-quality pure phase epitaxial domain single crystal structure, which has excellent application prospects.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a phase-pure two-dimensional halogen perovskite epitaxial homo / heterojunction material comprises the following steps:

[0007] 1) Synthesis of two-dimensional lead-based or tin-based halide perovskite bulk crystals using slow cooling crystallization method (L)2A n- 1B n X 3n+1 , wherein L is an organic ligand, which can be one or more of BA, PEA, 1T, 2T, 3T, etc., A is an organic small cation, which can be one or more of MA, FA, EA, etc., B is Pb or Sn, X is one or more of I, Br or Cl, and n is a positive integer such as 1, 2, or 3...;

[0008] 2) selecting single crystals from the bulk crystals obtained in 1), and mechanically exfoliating the single crystals to obtain two-dimensional halide perovskite sheets, transferring the two-dimensional halide perovskite sheets to a substrate, and then purifying the obtained two-dimensional halide perovskite sheets to remove the 3D phase therein, thereby obtaining two-dimensional halide perovskite single crystal sheets with high phase purity;

[0009] 3) Equipped for growing (L')2A' n-1 B' n X' 3n+1 wherein L' is an organic ligand, which can be one or more of BA, PEA, 1T, 2T, 3T, etc., A' is an organic small cation, which can be one or more of MA, FA, EA, etc., B' is Pb or Sn, X is one or more of I, Br or Cl, and n is a positive integer such as 1, 2, or 3 ...; chlorobenzene and the epitaxial growth solution are simultaneously dripped onto the pure phase single crystal (L) 2A obtained in 2) n-1 B n X 3n+1 The epitaxial growth is achieved on the substrate to obtain the (L)2A with pure phase in the epitaxial domain. n-1 B n X 3n+1 -(L')2A' n-1 B' n X' 3n+1 Epitaxial heterojunction or homojunction material, or simultaneously dropping chlorobenzene and the epitaxial growth solution on the prepared epitaxial heterojunction material for epitaxial growth, to achieve the preparation of multi-domain heterostructure.

[0010] In the above technical scheme, further, the slow cooling crystallization method specifically includes the following: adding relevant precursors and solvents according to the formula of the required synthetic two-dimensional halide perovskite material and storing them in a sealed container, heating to 90-100°C to completely dissolve the precursor in the solvent to obtain a clear precursor solution, then cooling the precursor solution to room temperature at a controlled rate, collecting the precipitated crystals and drying them, and storing them in an anhydrous environment.

[0011] Furthermore, in step 2), the bulk crystals obtained in 1) are mechanically exfoliated through iterative cycles of tape attachment and separation to form crystal flakes on the tape surface, and the tape with the crystal flakes is attached to a clean substrate, and heat-treated to promote close bonding between the wafer and the substrate. The temperature of the heating treatment can generally be 40 to 100°C. This step ensures that a large number of crystals are effectively transferred to the substrate, which is beneficial to subsequent large-scale epitaxy. High-quality two-dimensional halide perovskite sheets are prepared by mechanical exfoliation. Compared with 3D halide perovskites, 2D halide perovskites are easy to exfoliate and are more conducive to producing high-quality single crystals. After removing the tape, a substrate with pure phase single crystals attached is obtained.

[0012] Further, the purification treatment is to rinse or soak the two-dimensional halide perovskite sheet on the obtained substrate with a co-solvent of a weak polar solvent and isopropanol in a volume ratio of 1:50, and repeat it multiple times to remove the 3D phase therein. The weak polar solvent can generally be a weak polar solvent such as chlorobenzene (CB), toluene, dichlorobenzene, p-xylene, etc. In this step, the hydrophobicity of the organic ligand and the solubility difference between 2D and 3D perovskites are fully utilized to eliminate the 3D phase, thereby ensuring that the seed crystal has extremely high phase purity and maintaining a consistent plate thickness for subsequent kinetic Wulff-shaped epitaxial growth.

[0013] Furthermore, the preparation method of the epitaxial growth solution is as follows:

[0014] According to the (L')2A' n-1 B n X' 3n+1 The corresponding raw materials B'X', L'·HX' and A'X' when n>1 are dissolved in a co-solvent of a strong polar solvent / weak polar solvent to form a precursor stock solution, which is then diluted with a co-solvent of a weak polar solvent / acetonitrile to obtain an epitaxial growth solution.

[0015] Furthermore, the volume ratio of the strong polar solvent to the weak polar solvent in the strong polar solvent / weak polar solvent co-solvent is 1:0.1 to 1:2, and the volume ratio of the weak polar solvent to acetonitrile in the weak polar solvent / acetonitrile co-solvent is 2.5:0.5 to 2.5:1.5. Among them, the strong polar solvent is usually dimethylformamide, dimethyl sulfoxide or other strong polar solvents of similar polarity, and the weak polar solvent is usually chlorobenzene, toluene, dichlorobenzene, p-xylene and other similar weak polar solvents; the dosage ratio of B'X', L'·HX', A'X', and the co-solvent of the strong polar solvent / weak polar solvent can usually be 3-100 μmol: 10-150 μmol: 0-125 μmol: 1-4 ml, and the volume ratio of the precursor stock solution to the co-solvent of the weak polar solvent / acetonitrile can usually be 10-50: 1; when M' is Sn, tin powder is additionally added to the precursor stock solution to protect the divalent Sn cation.

[0016] Furthermore, the volume ratio of chlorobenzene to the epitaxial growth solution is 0.1:1 to 8:1, and the temperature during the epitaxial growth is 70 to 110°C, and the spontaneous nucleation of by-products is avoided by controlling the epitaxial growth time. When n=1 in the epitaxial structure domain, the epitaxial growth is controlled to be no longer than 5 minutes, and when n>1, the epitaxial growth is controlled to be no longer than 3 minutes, and the larger the n value, the shorter the epitaxial growth time is controlled.

[0017] Furthermore, in step 3), the diluted epitaxial growth solution is diluted again by 5 to 15 times, and then the resulting solution is dropped onto the growth substrate. The epitaxial growth process is limited to 1 minute and is quickly terminated before the solvent is completely evaporated, so that an ultra-narrow epitaxial domain can be obtained on the growth substrate.

[0018] The epitaxial growth method of the present invention can prepare homojunctions and heterojunctions, and can be applied to materials with high or low n values. In particular, the method of the prior art can only synthesize epitaxial heterojunctions with n=1, and is not applicable to epitaxial heterojunctions with high n values. When n exceeds 1, the common situation in the prior art is that two-dimensional halogen perovskites with different n values ​​coexist with three-dimensional phases. This mixed phase coexistence is a major obstacle to studying its photoelectric properties. Therefore, in order to meet this fundamental challenge, the present invention develops a kinetic Wulff-shaped heteroepitaxial growth method to achieve the preparation of epitaxial homojunctions and heterojunctions of two-dimensional halogen perovskites with a certain n value. In addition, the material obtained based on the method of the present invention can be directly used to construct devices. Since the size of the heterojunction materials synthesized by the methods in the prior art is often small, it is not conducive to direct device testing, and the method of the present invention can construct heterojunction materials of suitable size and realize device construction for the first time. All electronic devices of the present invention are manufactured based on heterostructures grown on silicon dioxide / silicon substrates. Mainly, van der Waals assembly technology is used to assemble graphite and h-BN thin film heterostructure devices. The fabrication of the device mainly includes sequentially transferring a graphite sheet, an h-BN sheet, and another graphite sheet on the obtained heterostructure. The graphite sheet is used as an electrode to conduct current in the tin domain and the lead domain, respectively, while the h-BN sheet is used as an insulating layer to avoid current leakage. This device structure ensures that the electronic properties at the tin / lead interface are measured. The electrical property measurement in the present invention is carried out on the probe of the Keithley2450 meter. During the electrical measurement, the IV curve was measured in a voltage range of -10V to 10V. The material of the present invention has a considerable rectification ratio, reliable rectification behavior, a relatively high rectification ratio, and repeatability of switching under electrical input and optical input conditions, highlighting the application capabilities of two-dimensional halogen perovskite epitaxial heterojunctions in optical isolators, low-power switches, and controlling unidirectional current in solar cells.

[0019] The beneficial effects of the present invention are:

[0020] The present invention has successfully developed a method for dynamic Wulff epitaxial growth and successfully constructed (3T)2MA with high phase purity. n-1 Pb n I 3n+1 -(3T)2MA n-1 Sn n I 3n+1(n=1,2,3) epitaxial heterojunction and other materials, which has never been achieved before. At the same time, the method of the present invention can construct an epitaxial heterojunction with a lattice mismatch greater than >11%, and the epitaxial domain can maintain a single crystal state. In addition, the present invention realizes and proves for the first time an ultra-narrow epitaxial heterojunction with an epitaxial width of less than 50nm, which is impossible to achieve with previous growth methods. Combined with multiple epitaxial growth techniques, it can successfully synthesize epitaxial superlattices with high periods and clear chemical structures; the method of the present invention is combined with van der Waals transfer technology to successfully realize high-quality two-dimensional halogen perovskite epitaxial heterostructure optoelectronic devices for the first time, which exhibits considerable rectification ratios and reliable electrical switching behaviors under optical / electrical input. The method of the present invention has extremely high application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 (3T)2MA2Pb3I in the present invention 10 Optical images, fluorescence images, powder XRD, and PL data graphs before and after crystal purification.

[0022] Figure 2 Optical and fluorescence images of epitaxially grown two-dimensional halogen perovskite homo- and heterojunctions (n=1) are presented, with XRD and PL data diagrams, including (3T)2SnI4-(3T)2SnI4 homojunction, (3T)2PbBr4-(3T)2SnI4, (3T)2PbCl4-(3T)2SnI4, and (3T)2PbCl4-(3T)2PbI4 heterojunctions (lattice mismatch greater than >11%).

[0023] Figure 3 For large-scale (3T)2MA n-1 Pb n I 3n+1 -(3T)2MA n-1 Sn n I 3n+1 (n=1,2,3) Optical and fluorescence images of epitaxial heterojunctions, as well as XRD and PL data plots.

[0024] Figure 4It is a high-period multi-heterojunction (3T)2MAPb2I7-(3T)2MASn2I7-(3T)2MAPb2I7, (3T)2MAPb2I7-(3T)2MASn2I7-(3T)2MAPb2I7-(3T)2MASn2I7, (3T)2MASn2I7-(3T)2MAPb2I7-(3T)2MASn2I7 , optical and fluorescence images of {(3T)2MASn2I7-(3T)2MAPb2I7}×3-(3T)2MASn2I7 and optical and SEM images of ultra-narrow epitaxial heterojunctions (3T)2PbI4-(3T)2SnI4-(3T)2PbI4 and (3T)2SnI4-(3T)2PbI4-(3T)2SnI4 with an epitaxial width of less than 50nm.

[0025] Figure 5 Schematic diagram and example diagram of the (3T)2MAPb2I7-(3T)2MASn2I7 heterostructure optoelectronic device constructed for the first time in the present invention, as well as data diagrams of its high rectification ratio and its use as a low-power electrical switch and optical switch.

[0026] Figure 6 This is the data diagram of the (3T)2PbI4-(3T)2SnI4 heterostructure constructed for the first time in the present invention as a low-power electrical switch and optical switch. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific examples, but the present invention is not limited to the following examples. The methods involved are conventional methods unless otherwise specified. The raw materials involved can be obtained from public commercial channels unless otherwise specified.

[0028] Example 1

[0029] 1) Bulk crystal preparation

[0030] Using the slow cooling crystallization method, 0.0047mmol 3T·HI, 0.015mmol MAI, 0.05mmol metal salt PbI, 0.2mL HI, 0.1mL H3PO2, and 1.5mL IPA were added into a sealed container and heated to 90°C to obtain a clear precursor solution. The precursor solution was then cooled to room temperature at a controlled rate of 1°C / h. The precipitated crystals were collected and dried and stored in an anhydrous environment. The obtained block crystals (3T)2MA2Pb3I 10 The optical images, fluorescence images, PL data, and powder XRD are shown in Figure 2. Figure 1 As shown in a1 to a4.

[0031] The slow cooling crystallization method is a conventional method for preparing two-dimensional halide perovskite bulk crystal materials, and the following operations can usually be used: according to the formula of the desired two-dimensional halide perovskite material, the relevant precursor and solvent are added and stored in a sealed container, heated to 90-100°C, so that the precursor is completely dissolved in the solvent to obtain a clear precursor solution, and then the precursor solution is cooled to room temperature at a controlled rate of usually several degrees Celsius per hour or even lower (such as 1°C / h in the embodiment of the present application), the precipitated crystals are collected and dried, and stored in an anhydrous environment. Some of the two-dimensional halide perovskite bulk crystal materials involved in the embodiments of the present application are prepared by this method, and the corresponding raw materials and materials are shown in Table 1, wherein the metal salt is the corresponding halide salt corresponding to the metal (lead or tin) and the halogen atom in the material.

[0032] Table 1

[0033]

[0034] 2) Stripping and crystal purification

[0035] The bulk crystal obtained in 1) is subjected to mechanical exfoliation through iterative cycles of tape attachment and detachment to obtain a two-dimensional halogen perovskite flake. The tape with the flake is attached to a clean substrate and heated at 60°C to promote close bonding between the wafer and the substrate, after which the tape is gently peeled off. Compared with three-dimensional halogen perovskites, two-dimensional halogen perovskite flakes are easy to peel off, thereby obtaining high-quality single crystals. Figure 1 As can be seen from b1 to b4, although the exfoliated two-dimensional halide perovskite flakes have a single PL emission, the powder XRD results show the presence of a three-dimensional phase component ( Figure 1 Considering the hydrophobicity of 3T organic ligands and the difference in solubility between 2D and 3D halide perovskites in polar solvents, a co-solvent of moderately polar chlorobenzene and isopropanol (volume ratio of 1:50) was used to selectively remove (3T)2MA2Pb3I 10 The three-dimensional phase in the single crystal. The exfoliated thin slice was washed with the co-solvent, and after three washes, the three-dimensional phase was removed, which was confirmed by PXRD and PL spectra ( Figure 1 c4), thereby ensuring that the seed crystal has extremely high phase purity and consistent n value, which can be used for subsequent Wulff-type epitaxial growth.

[0036] The same method can be used to peel and purify other bulk crystals obtained in Table 1 for subsequent epitaxial growth, which will not be described in detail in the subsequent embodiments. The epitaxial growth method of the present invention is well applicable to materials with different n values. The following embodiments illustrate epitaxial growth with different n values ​​respectively:

[0037] Example 2

[0038] Epitaxial growth of two-dimensional halide perovskite homo- and heterojunctions (n=1):

[0039] 1. Preparation of epitaxial growth solution

[0040] 1). For epitaxial growth of (3T)2SnI4 domains: 20 μmol of SnI2 and 20 μmol of 3T·HI were dissolved in 2 mL of dimethylformamide / chlorobenzene co-solvent (1:1 by volume) to prepare a precursor stock solution. The (3T)2SnI4 epitaxial growth solution was prepared by further diluting the stock solution (120 μL) with chlorobenzene / acetonitrile co-solvent (2.5:1 by volume, 3.5 mL).

[0041] 2) For epitaxial (3T)2PbI4 domains: 13μmol of PbI2 and 20μmol of 3T·HI were dissolved in 2mL of dimethylformamide / chlorobenzene co-solvent (volume ratio of 1:1) to prepare a precursor stock solution. The stock solution (120μL) was further diluted with chlorobenzene / acetonitrile co-solvent (volume ratio of 1.8:1, 2.8mL) to prepare the (3T)2PbI4 epitaxial growth solution.

[0042] Note: Tin powder (~50 mg) was added to the precursor stock solution in 1) above to protect the divalent Sn cations.

[0043] 2. Epitaxial Growth

[0044] 1). (3T)2SnI4-(3T)2SnI4 homogeneous structure: 60μL CB and 20μL diluted (3T)2SnI4 epitaxial growth solution were dropped onto a substrate (attached with a (3T)2SnI4 thin film after peeling and purification) placed in a capless glass bottle, and epitaxial growth was achieved under heating conditions of 70°C to obtain a (3T)2SnI4-(3T)2SnI4 homogeneous structure.

[0045] 2). (3T)2PbI4-(3T)2SnI4 heterostructure: 60μL CB and 20μL diluted (3T)2SnI4 epitaxial growth solution were dropped onto a substrate (attached with a (3T)2PbI4 thin film after peeling and purification) placed in a capless glass bottle, and epitaxial growth was achieved under heating at 70°C to obtain a (3T)2PbI4-(3T)2SnI4 heterostructure.

[0046] 3). (3T)2PbBr4-(3T)2SnI4 heterostructure. 70μL CB and 20μL diluted (3T)2SnI4 epitaxial growth solution were dropped onto a substrate (attached with a (3T)2PbBr4 flake after peeling and purification) placed in a capless glass bottle, and epitaxial growth was achieved at 80°C to obtain a (3T)2PbBr4-(3T)2SnI4 heterostructure.

[0047] 4). (3T)2PbCl4-(3T)2SnI4 heterostructure. 60μL CB and 15μL diluted (3T)2SnI4 epitaxial growth solution were dropped onto a substrate (attached with a (3T)2PbCl4 flake after peeling and purification) placed in a capless glass bottle, and epitaxial growth was achieved at 70°C to obtain a (3T)2PbCl4-(3T)2SnI4 heterostructure.

[0048] 5). (3T)2PbCl4-(3T)2PbI4 heterostructure. 5μL CB and 10μL diluted (3T)2PbI4 epitaxial growth solution were dropped onto a substrate (attached with a (3T)2PbCl4 flake after peeling and purification) placed in a capless glass bottle, and epitaxial growth was achieved at 110°C to obtain a (3T)2PbCl4-(3T)2PbI4 heterostructure.

[0049] For these heterostructures (n=1), complete evaporation of the solvent typically required ~30 min. To avoid spontaneous nucleation of byproducts, the heteroepitaxial growth was interrupted after ~5 min.

[0050] The optical and fluorescence images of (3T)2SnI4-(3T)2SnI4 homojunction, (3T)2PbBr4-(3T)2SnI4 heterojunction, (3T)2PbCl4-(3T)2SnI4 heterojunction, and (3T)2PbCl4-(3T)2PbI4 heterojunction are shown in Figure 2. Figure 2 The XRD and PL data are shown in a, b, c, and d. Figure 2 As shown in e and f. It can be seen that the method of the present invention can not only successfully produce homojunction and heterojunction structures, but also can successfully construct heterojunction structures with large lattice mismatch (lattice mismatch can reach more than 11%), and the epitaxial domain can maintain a single crystal state. The optical and fluorescence images, powder XRD, and PL data of the (3T)2PbI4-(3T)2SnI4 heterojunction are shown in Figure 1. Figure 3 As shown in a, b, and c.

[0051] Example 3

[0052] Epitaxial growth of 2D halide perovskite heterojunctions (n>1):

[0053] 1. Preparation of epitaxial growth solution

[0054] 1). For epitaxial growth of (3T)2MASn2I7 domains: 30 μmol of SnI2, 20 μmol of 3T·HI and 30 μmol of MAI were dissolved in 2 mL of dimethylformamide / chlorobenzene co-solvent (volume ratio of 1:1) to prepare a precursor stock solution. The stock solution (120 μL) was further diluted with chlorobenzene / acetonitrile co-solvent (volume ratio of 2.5:1, 3.5 mL) to prepare the (3T)2MASn2I7 epitaxial growth solution.

[0055] 2). For epitaxial (3T) 2MA2Sn3I 10 Domain: 90 μmol SnI2, 20 μmol 3T·HI and 60 μmol MAI were dissolved in 2 mL of dimethylformamide / chlorobenzene cosolvent (volume ratio 1:1) to prepare a precursor stock solution. The stock solution (120 μL) was further diluted with chlorobenzene / acetonitrile cosolvent (volume ratio 2.5:1, 3.5 mL) to prepare (3T)2MA2Sn3I 10 Epitaxial growth solution.

[0056] 3) For epitaxial (3T)2MAPb2I7 domains: 25 μmol of PbI2, 20 μmol of 3T·HI and 40 μmol of MAI were dissolved in 2 mL of dimethylformamide / chlorobenzene co-solvent (volume ratio of 1:1). The stock solution (120 μL) was further diluted with chlorobenzene / acetonitrile co-solvent (volume ratio of 1.5:1, 2.5 mL) to prepare the (3T)2MAPb2I7 epitaxial growth solution.

[0057] Note: Tin powder (~50 mg) was added to the precursor stock solutions of 1) and 2) to protect the divalent Sn cations.

[0058] 2. Epitaxial Growth

[0059] 1) (3T)2MAPb2I7-(3T)2MASn2I7 heterostructure. 60 μL CB and 30 μL diluted (3T)2MASn2I7 epitaxial growth solution were dropped onto a substrate (attached with a (3T)2MAPb2I7 flake after exfoliation and purification) placed in a capless glass bottle, and epitaxial growth was carried out at 80 °C. In order to avoid the spontaneous nucleation of by-products (i.e., two-dimensional halide perovskites or three-dimensional perovskites with different n values), the heteroepitaxial growth was interrupted halfway (growth for 2-3 minutes).

[0060] 2)(3T)2MA2Pb3I 10 -(3T)2MA2Sn3I 10 Heterostructure. 80 μL CB and 20 μL diluted (3T)2MA2Sn3I 10The epitaxial growth solution is dropped onto the substrate (attached with the (3T)2MA2Pb3I2O3 after stripping and purification) placed in a capless glass bottle. 10 The epitaxial growth was carried out at 80° C. In order to avoid the spontaneous nucleation of by-products (i.e., two-dimensional halide perovskites or three-dimensional perovskites with different n values), the heteroepitaxial growth was interrupted halfway (growth time 1-2 minutes).

[0061] Figure 3 d~f and g~i are (3T)2MAPb2I7-(3T)2MASn2I7 heterostructure and (3T2MA2Pb3I 10 -(3T)2MA2Sn3I 10 From the optical and fluorescence images, powder XRD and PL data of the heterostructures, it can be seen that the method of the present invention not only successfully synthesizes heterostructures with different n values, but also has high phase purity. At the same time, a large number of heterostructures can be obtained at one time, which can be prepared on a large scale.

[0062] Example 4

[0063] Epitaxial growth of two-dimensional halide perovskite multi-heterojunctions:

[0064] On the basis of the grown (3T)2MAPb2I7-(3T)2MASn2I7 heterostructure, 40μL CB and 50μL diluted (3T)2MAPb2I7 epitaxial growth solution were added to start the further epitaxial growth process. This step produced a (3T)2MAPb2I7-(3T)2MASn2I7-(3T)2MAPb2I7 multi-domain heterostructure, as shown in Figure 4 Then, 60 μL CB and 40 μL diluted (3T)2MASn2I7 epitaxial growth solution were added simultaneously to epitaxially grow the (3T)2MASn2I7 layer as the outermost layer, as shown in FIG. Figure 4 This method can also be used to construct double-domain and multi-domain heterostructures with (3T)2MASn2I7 as the starting domain. By repeating this continuous process, more complex heterostructures were synthesized, such as (3T)2MASn2I7-(3T)2MAPb2I7-(3T)2MASn2I7 heterostructures. Figure 4 In c, {(3T)2MASn2I7-(3T)2MAPb2I7}×3-(3T)2MASn2I7 multiple heterostructures, such as Figure 4 Middle d. The temperature was maintained at 75 °C throughout the growth cycle to ensure optimal conditions for epitaxial growth.

[0065] Example 5

[0066] Ultra-narrow multi-heterostructures:

[0067] The (3T)2PbI4 crystal sheets after peeling and purification were obtained on the substrate. Subsequently, 40μL CB and 20μL diluted (3T)2PbI4 epitaxial growth solution (prepared in Example 2) were dropped on the substrate and then heated at 80°C to cause the solvent to evaporate. After 20 minutes of heating, the solvent was completely evaporated, and a large number of rectangular (3T)2PbI4 flakes appeared on the substrate. In order to obtain ultra-narrow (3T)2SnI4 domain width, the initially diluted (3T)2SnI4 epitaxial growth solution (prepared in Example 2) was diluted ten times again with chlorobenzene / acetonitrile co-solvent (volume ratio of 2.5:1), and the duration of epitaxial growth was shortened. 20μL of further diluted (3T)2SnI4 epitaxial growth solution was dropped on the growth substrate to start the epitaxial growth of ultra-narrow (3T)2SnI4 domains. The epitaxial growth process was limited to about 1 minute and terminated quickly before the solvent was completely evaporated. Subsequently, 40 μL of CB and 30 μL of the diluted (3T)2PbI4 epitaxial growth solution (prepared in Example 2) were sequentially added to the same substrate, and then heated at 80° C. After the solvent was completely evaporated, a large number of (3T)2PbI4-(3T)2SnI4-(3T)2PbI4 multi-heterostructures with ultra-narrow (3T)2SnI4 domains were obtained. Similarly, this method can also be used to obtain (3T)2SnI4-(3T)2PbI4-(3T)2SnI4 multi-heterostructures with ultra-narrow (3T)2PbI4 domains, such as Figure 4 As shown in e and f.

[0068] Example 6

[0069] Research on optoelectronic devices based on the synthetic materials of this invention:

[0070] exist Figure 5As shown, the transferred h-BN and graphite sheets are combined to build a device for the (3T)2MAPb2I7-(3T)2MASn2I7 heterostructure. One of the electrodes is made by transferring a piece of exfoliated graphite directly to the (3T)2MASn2I7 domain at the periphery of the heterostructure, while the other electrode needs to contact only the (3T)2MAPb2I7 domain inside the heterostructure. However, the lead domain is surrounded by the (3T)2MASn2I7, i.e., the tin domain, in the heterostructure, which makes the preparation of the other electrode challenging. To solve this problem, the present invention uses an h-BN sheet as an insulating layer to cover one side of the heterostructure, and then transfers another piece of exfoliated graphite to the side to make the graphite contact the lead domain, which helps to inject charge directly from the graphite electrode into the lead domain without leaking current to the tin domain. The heterostructure devices with different n values ​​were fabricated by the same method. The IV test results of heterostructures with different n values ​​showed that when the n value was 1-3, the rectification ratios of the Pb-Sn epitaxial heterostructure were approximately 1000, 1000, and 20, respectively. Figure 5 In addition, an input alternating voltage was applied to the (3T)2MAPb2I7-(3T)2MASn2I7 heterostructure device (n=2), and the output current signal was recorded using a probe station. The heterostructure was in the on state (I=7nA) under forward bias (10V), and completely blocked (off state, I~-17pA) under reverse bias (-10V), as shown in Figure 2. Figure 5 As shown in d. Figure 6 As shown in Figure 2, the n=1 heterostructure also has similar electrical rectification characteristics. In addition, considering their stable reverse saturation current, these heterostructures (n=1 and 2) are stable under periodic pulsed light (580 nm and 0.6 mW / cm 2 , Figure 5 Middle e, Figure 6 b) also exhibits stable switching behavior under illumination. The relatively high rectification ratio and the repeatability of switching under both electrical and optical input conditions highlight the application of 2D halide perovskite epitaxial heterostructures in optical isolators, low-power switches, and controlling unidirectional current in solar cells.

[0071] The above-described embodiments are only some of the preferred solutions of the present invention, but they are not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material, characterized in that: These include: 1) Synthesis of two-dimensional lead-based or tin-based halide perovskite bulk crystals using slow cooling crystallization method (L)2A n-1 B n X 3n+1 , wherein L is an organic ligand selected from one or more of BA, PEA, 1T, 2T, and 3T, A is an organic small cation selected from one or more of MA, FA, and EA, B is Pb or Sn, X is one or more of I, Br, or Cl, and n is a positive integer; 2) selecting single crystals from the bulk crystals obtained in 1), and mechanically exfoliating the single crystals to obtain two-dimensional halide perovskite sheets, transferring the two-dimensional halide perovskite sheets to a substrate, and then purifying the obtained two-dimensional halide perovskite sheets to remove the 3D phase therein, thereby obtaining two-dimensional halide perovskite single crystal sheets with high phase purity; 3) Equipped for growing (L')2A' n-1 B' n X' 3n+1 wherein L' is an organic ligand selected from one or more of BA, PEA, 1T, 2T, and 3T, A' is an organic small cation selected from one or more of MA, FA, and EA, B' is Pb or Sn, X' is one or more of I, Br, or Cl, and n is a positive integer; simultaneously dropping chlorobenzene and the epitaxial growth solution onto the pure phase single crystal (L)2A obtained in 2) n-1 B n X 3n+1 The epitaxial growth is achieved on the substrate to obtain the (L)2A with pure phase in the epitaxial domain. n-1 B n X 3n+1 -(L')2A' n-1 B' n X' 3n+1 Epitaxial heterojunction or homojunction material, or simultaneously dropping chlorobenzene and the epitaxial growth solution on the prepared epitaxial heterojunction material for epitaxial growth, to achieve the preparation of multi-domain heterostructure.

2. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 1, characterized in that: The slow cooling crystallization method specifically includes the following steps: adding relevant precursors and solvents according to the formula of the desired two-dimensional halide perovskite material and storing them in a sealed container, heating to 90-100°C to completely dissolve the precursor in the solvent to obtain a clear precursor solution, then cooling the precursor solution to room temperature at a controlled rate, collecting the precipitated crystals, drying them, and storing them in an anhydrous environment.

3. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 1, characterized in that: In step 2), the block crystal obtained in 1) is mechanically exfoliated through iterative cycles of tape attachment and detachment to form a crystal flake on the tape surface. The tape with the crystal flake is attached to a clean substrate and heated to promote close bonding between the chip and the substrate.

4. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 1, characterized in that: The purification treatment is as follows: the two-dimensional halide perovskite sheet on the obtained substrate is rinsed or soaked with a co-solvent of a weak polar solvent and isopropanol in a volume ratio of 1:50, and the process is repeated multiple times to remove the 3D phase therein.

5. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 1, characterized in that: The preparation method of the epitaxial growth solution is as follows: According to (L')2A' n-1 B' n X' 3n+1 The corresponding raw materials B'X', L'·HX' and A'X' when n>1 are dissolved in a co-solvent of a strong polar solvent / weak polar solvent to form a precursor stock solution, which is then diluted with a co-solvent of a weak polar solvent / acetonitrile to obtain an epitaxial growth solution.

6. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 5, characterized in that: The volume ratio of the strong polar solvent to the weak polar solvent is 1:0.1 to 1:2, and the volume ratio of the weak polar solvent to acetonitrile is 2.5:0.5 to 2.5:1.

5.

7. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 1, characterized in that: The volume ratio of the chlorobenzene to the epitaxial growth solution is 0.1:1 to 8:

1. During the epitaxial growth, the temperature is controlled to be 70 to 110°C, and the spontaneous nucleation of by-products is avoided by controlling the epitaxial growth time: when n=1 in the epitaxial structure domain, the epitaxial growth is controlled to be no longer than 5 minutes; when n>1, the epitaxial growth is controlled to be no longer than 3 minutes; the larger the n value, the shorter the epitaxial growth time.

8. The method for preparing a pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material according to claim 1, characterized in that: In step 3), the diluted epitaxial growth solution is diluted again by 5 to 15 times, and then the resulting solution is dropped onto the growth substrate. The epitaxial growth process is limited to 1 minute and is quickly terminated before the solvent is completely evaporated, so that an ultra-narrow epitaxial domain can be obtained on the growth substrate.

9. A pure phase two-dimensional halogen perovskite epitaxial homo / heterojunction material, characterized in that: The method is prepared by the method according to any one of claims 1 to 8.

10. A device, characterized in that The heterojunction material according to claim 9 is prepared by using van der Waals assembly technology, including sequentially transferring a graphite sheet, an h-BN sheet and another graphite sheet on the obtained heterostructure material, wherein the two graphite sheets are respectively used as electrodes to conduct current in the tin domain or the lead domain, and the h-BN sheet is used as an insulating layer to avoid current leakage.

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