Method for epitaxial growth of perovskite single crystal heterojunction

Abstract

The invention discloses a method for epitaxial growth of a perovskite single crystal heterojunction. According to the method, a saturated acid solution of a specific solute is selected, heteroepitaxy is carried out on different types of perovskite layers, a perovskite lattice structure of a mother layer on the surface of a substrate is flexibly changed, the problem of lattice mismatch caused by lattice mutation at a heterojunction due to heteroepitaxy is solved, the defect density of a material at the heterojunction is reduced, and the performance of the device is improved. The heteroepitaxy yield is improved, and the epitaxial growth crystal quality of the perovskite material is improved. The method comprises the following specific steps: putting a perovskite substrate into a specific saturated acid solution, cooling to separate out crystals, and carrying out heteroepitaxial growth. According to the method, the heteroepitaxy yield of the perovskite material is remarkably improved, the heterojunction defect density is reduced, and the method has wide application potential.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor materials technology, and particularly relates to a method for epitaxial growth of perovskite single crystal heterojunctions. Background Technology

[0002] Perovskite materials, due to their excellent photoelectric properties (such as high absorption coefficient, long carrier diffusion length, and tunable bandgap), have shown great application potential in fields such as solar cells, light-emitting diodes (LEDs), and photodetectors. Among them, perovskite heterostructures (such as MAPbI3 / MAPbBr3, CsPbBr3 / CsPbCl3, etc.) can further optimize device performance by combining the characteristics of different halogen components, for example, by broadening the light absorption range, improving carrier separation efficiency, and enhancing interface stability. However, the preparation of perovskite heterostructures faces many technical challenges, especially in the heteroepitaxial growth process, where precise control of the interface structure and lattice matching are crucial issues. Currently, the preparation of perovskite heterostructures mainly relies on two methods: organic solvent heteroepitaxial growth and high-temperature vapor deposition. Organic solvents used in heteroepitaxial methods (such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL)) exhibit strong solubility for almost all metal halide perovskites (3D, 2D, organic or inorganic perovskite materials), rapidly dissolving the perovskite substrate surface, destroying the crystal structure, and hindering effective heteroepitaxial growth. High-temperature vapor deposition (HCVD) requires precise control of temperature, pressure, and gas flow, placing high demands on equipment. Furthermore, perovskite materials are prone to decomposition at high temperatures, leading to substrate structure damage or increased interface defects. Therefore, neither organic solvent methods nor HCVD can simultaneously meet the requirements of precise interface structure control, process universality, and mild process characteristics. Thus, a mild epitaxial method that allows for precise control of interface reactions and is applicable to multiple types of perovskites is urgently needed. Summary of the Invention

[0003] To address the above-mentioned technical problems, this invention provides a method for epitaxial growth of perovskite single-crystal heterostructures. The method of this invention can form a halogen gradient transition layer between the substrate perovskite and the target halide, which helps to alleviate the problem of lattice mismatch, thereby obtaining a high-quality perovskite heterostructure.

[0004] To achieve the above objectives, the technical solution of the present invention is as follows: A method for epitaxial growth of perovskite single-crystal heterojunctions includes the following steps: S1: Obtain a saturated acid solution S101: Dissolve the metal salt corresponding to the target halide perovskite in hydrobromic acid solution to form a first saturated solution; S102: Mix hydrobromic acid solution with organic amine solution or cesium salt to form a second mixed solution; S103: After mixing the first saturated solution and the second mixed solution, the mixture is allowed to stand and age at a preset temperature to form a stable saturated acid solution system; wherein steps S101 and S102 are not in any particular order. S2: Perovskite heteroepitaxial growth S201: Immerse the substrate perovskite in the saturated acid solution of step S1 and carry out an ion exchange reaction at a preset temperature to form a halogen gradient transition layer on the substrate perovskite. S202: The target halide perovskite is oriented and epitaxially grown on the surface of the halogen gradient transition layer by a cooling crystallization method.

[0005] Preferably, the temperature for static aging in step S103 is 60-90℃.

[0006] Preferably, the static aging time in step S103 is 12-24 hours.

[0007] Preferably, in step S201, the ion exchange reaction is carried out at 60-90°C for 10-30 minutes.

[0008] Preferably, in step S202, the temperature is reduced to 20-30°C at a cooling rate of 0.5-5°C / min. This cooling reduces the solubility of the target halide perovskite in the acid solution, causing it to precipitate directionally on the surface of the halogen gradient transition layer, thereby achieving heteroepitaxialization.

[0009] Preferably, the organic amine is any one of methylamine, ethylamine, phenylethylamine, or n-butylamine.

[0010] Preferably, the metal salt corresponding to the target halide perovskite is any one or a mixture of several of lead oxide, tin oxide, lead halide, tin halide, nitrate, or lead acetate.

[0011] Preferably, the substrate perovskite is a three-dimensional perovskite, a two-dimensional perovskite, or an inorganic perovskite; The target halide perovskite is a material with a different halogen composition from the surface of the substrate perovskite.

[0012] Because the present invention adopts the above technical solution, it has the following advantages and positive effects compared with the prior art: Given that acid solutions have low solubility in perovskite materials, this invention uses acid solutions as solvents for precursor solutions of target halide perovskites, which can suppress over-protection of the substrate perovskite and protect the interface structure.

[0013] A perovskite substrate is immersed in a saturated acid solution, and an ion exchange reaction is carried out at a predetermined temperature. During the reaction, active hydrogen ions (H⁺) in the acid solution activate halide ions (such as I⁻, Br⁻, Cl⁻) on the surface of the perovskite substrate, promoting their exchange with halide ions (such as Br⁻, Cl⁻, I⁻) in the acid solution, forming a halogen gradient transition layer (such as MAPbI₂). x Br 3-x (PEA)2PbI x Cl 4-x CsPbBr x Cl 3-x (etc.), where the value of x increases from the surface to the interior, alleviating lattice mismatch.

[0014] By controlling temperature changes and adjusting the cooling process to reduce the solubility of the target halide perovskite in acid solution, it is oriented to precipitate on the surface of the halogen gradient transition layer, thus achieving heteroepitaxialization.

[0015] This invention is applicable to heteroepitaxial growth of three-dimensional, two-dimensional, organic or inorganic perovskite materials. Attached Figure Description

[0016] Figure 1 This is an electron microscope image of the MAPbI3 single crystal surface obtained after epitaxial growth in acidic solution for 80 minutes in Example 1 of this invention; Figure 2 This is an electron microscope image of the crystal cross-section obtained after 80 minutes of epitaxial growth in acidic solution in Example 1 of the present invention; Figure 3 This is an electron microscope image of the MAPbI3 single crystal surface obtained after 30 minutes of organic solution epitaxial growth in Example 2 of the present invention. Figure 4 This is an electron microscope image of the crystal cross-section obtained after 30 minutes of epitaxial growth in acidic solution in Example 2 of the present invention; Figure 5 This is an electron microscope image of the MAPbI3 single crystal surface obtained after 30 minutes of organic solution epitaxial growth in Comparative Example 1 of this invention. Figure 6 This is an electron microscope image of the MAPbI3 single crystal surface obtained after 2 hours of organic solution epitaxial growth in Comparative Example 1 of this invention; Figure 7 This is an electron microscope image of the cross-section of a crystal obtained after 2 hours of organic solution epitaxial growth in Comparative Example 1 of this invention; Figure 8 This is an electron microscope image of the MAPbI3 single crystal surface obtained after 80 minutes of organic solution epitaxial growth in Comparative Example 2 of this invention. Figure 9 This is an electron microscope image of the MAPbI3 single crystal surface obtained after 80 minutes of organic solution epitaxial growth in Comparative Example 3 of this invention. Detailed Implementation

[0017] This invention provides a method for epitaxial growth of perovskite single-crystal heterojunctions. This method involves selecting a saturated acidic solution with a specific solute to perform heteroepitaxial growth on different types of perovskite layers. This flexibly alters the lattice structure of the parent perovskite layer on the substrate surface, alleviating the lattice mismatch problem caused by lattice abrupt changes at the heterojunction due to heteroepitaxial growth, reducing the material defect density at the heterojunction, improving the yield of heteroepitaxial growth, and improving the crystal quality of epitaxially grown perovskite materials. It has broad application potential.

[0018] This invention achieves controllable epitaxial growth of perovskite heterostructures by promoting halide ion exchange through active hydrogen ions (H⁺) in acidic solutions and combining this with temperature gradient-induced solubility changes. Its core lies in: 1. Saturated acid solution system design: Select an acidic solution (such as hydrobromic acid, hydroiodic acid, hydrochloric acid or other mixed acid) that matches the target halide perovskite material (ABX3 type perovskite material, where the A-site cation can be methylamine ion (MA), methylammonium ion (FA), cesium ion (Cs), the B-site is lead (Pb) or tin (Sn), and the X-site anion can be chloride ion (Cl), bromide ion (Br), iodide ion (I) etc.) to form a low solubility environment and avoid excessive dissolution of the substrate perovskite.

[0019] 2. Ion Exchange-Induced Interface Reconstruction: H⁺ in acid solution activates halide ions (such as Cl⁻, Br⁻, I⁻) on the perovskite surface, promoting their exchange with halide ions (such as Cl⁻, Br⁻, I⁻) in the acid solution, forming a halogen gradient transition layer (such as MAPbI₂). x Br 3-x ;MAPbCl x Br 3-x ;FAPbI x Br 3-x (e.g., x increases from the surface to the interior), providing a matching lattice for heteroepitaxial growth.

[0020] 3. Temperature gradient driven epitaxial growth: By lowering the temperature, the solubility of the target halide perovskite (such as MAPbBr3, (PEA)2PbCl4, CsPbCl3, etc.) in the acid solution is reduced, causing it to precipitate directionally on the pre-reconstructed substrate surface, thus achieving heteroepitaxial growth.

[0021] The method for epitaxial growth of perovskite single-crystal heterojunctions proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description.

[0022] In the following examples, the concentration of hydrobromic acid solution was 8.815 mol / L and the concentration of methylamine solution was 11.6 mol / L.

[0023] Example 1 1. First, prepare a saturated acid solution: Dissolve 2.93g of lead acetate in 10ml of hydrobromic acid (HBr) solution to form the first saturated solution; slowly add 2ml of hydrobromic acid (HBr) solution to 800µL of methylamine solution to form the second mixed solution. Mix the first saturated solution and the second mixed solution in a 20ml glass bottle, and then place it on a 70℃ hot plate for 12 hours.

[0024] 2. Place the MAPbI3 single crystal in the MAPbBr3 saturated acidic solution prepared above and let it stand at 70°C for 20 minutes to form a transition layer on the surface of the MAPbI3 single crystal by displacement. 3. Cool the saturated acidic solution of MAPbBr3 to 30℃ at a rate of 0.5℃ / min to carry out epitaxial growth.

[0025] from Figure 1 It can be clearly observed that the MAPbBr3 single crystal surface obtained by epitaxial growth on the MAPbI3 single crystal surface through acidic solution is very smooth, and its morphology is almost the same as that of the crystal surface obtained by conventional reverse temperature crystallization method, indicating that the acidic solution epitaxial method can achieve high-quality epitaxial growth. Figure 2 The cross-sectional images further reveal the key mechanism of epitaxial growth: compared with traditional organic solution epitaxy (Comparative Example 1), acidic solutions have lower solubility for perovskite materials. This characteristic effectively protects the lattice structure of the substrate surface, avoiding surface etching and lattice damage caused by excessive dissolution. Furthermore, active hydrogen ions (H⁺) in the acidic solution can activate iodide ions (I⁻) on the MAPbI₃ surface, significantly promoting ion exchange between I⁻ and bromide ions (Br⁻) in the solution, thereby forming a halogen gradient transition layer (MAPbI₃) on the substrate surface. x Br 3-x This gradient transition layer not only alleviates the lattice mismatch between the epitaxial layer and the substrate, but also provides an ideal lattice template for the epitaxial growth of MAPbBr3, ensuring the flatness and crystal quality of the epitaxial layer.

[0026] Example 2 1. First, prepare a saturated acid solution: Dissolve 2.93g of lead acetate in 10ml of hydrobromic acid (HBr) solution to form the first saturated solution; slowly add 2ml of hydrobromic acid (HBr) solution to 800µL of methylamine solution to form the second mixed solution. Mix the first saturated solution and the second mixed solution in a 20ml glass bottle, and then place it on a 70℃ hot plate for 12 hours.

[0027] 2. Place the MAPbI3 single crystal in the MAPbBr3 saturated acidic solution prepared above and let it stand at 70°C for 20 minutes to form a transition layer on the surface of the MAPbI3 single crystal by displacement. 3. Cool the saturated acidic solution of MAPbBr3 to 30℃ at a rate of 1.5℃ / min to carry out epitaxial growth.

[0028] from Figure 3 It can be clearly observed that the MAPbBr3 single crystal epitaxially grown on the surface of MAPbI3 single crystal through acidic solution has a relatively smooth surface morphology. This is in contrast to the crystal obtained under a cooling rate of 0.5℃ / min. Figure 1 Compared to the previous method, the surface smoothness of the crystals grown in this study differs. This is mainly attributed to the fact that a faster cooling rate leads to a higher solute precipitation rate, thereby accelerating the crystallization process and ultimately resulting in a decrease in crystal surface smoothness. Furthermore, the cross-sectional image of the crystal at this cooling rate (…) Figure 4 As can be seen, its cross-sectional morphology is not significantly different from that under the condition of 0.5℃ / min, which further confirms that the acid solution epitaxy method has good reliability.

[0029] Comparative Example 1 The preparation method is as follows: 1. Dissolve the perovskite precursor raw materials methylamine hydrobromide (MAI) and lead bromide (PbI2) in N,N-dimethylformamide (DMF) at a molar ratio of 1:1, and obtain a MAPbI3 perovskite precursor solution with a concentration of 1.25 mol by filtration; obtain a MAPbBr3 perovskite precursor solution with a concentration of 1.8 mol by the same steps.

[0030] 2. Add a certain amount of perovskite precursor solution to a petri dish and place it on a constant temperature hot plate at 70℃ for 2 hours to obtain perovskite seed crystals with a size of less than 1 mm.

[0031] 3. Transfer the obtained perovskite seed crystal to a glass bottle, add the perovskite precursor solution, and place the glass bottle on a hot plate at 110°C for 24 hours to obtain MAPbI3 perovskite single crystal.

[0032] 4. Place the obtained MAPbI3 perovskite single crystal into a glass containing 1.8 mol of MAPbBr3 perovskite precursor solution, and place the glass bottle at 40°C for epitaxial growth.

[0033] Figure 5 and Figure 6 These are optical micrographs of the surface of MAPbI3 perovskite single crystals after epitaxial growth in organic solution for different times. Figure 5 The surface morphology of the single crystal was shown 30 minutes after epitaxial growth. Figure 6The image shows the surface morphology of the single crystal two hours after epitaxial growth. It is clearly observed from the image that the epitaxially grown MAPbBr3 single crystal exhibits an irregular morphology on the MAPbI3 single crystal surface. This irregular growth phenomenon is mainly attributed to the dissolution effect of DMF (N,N-dimethylformamide) solvent on the MAPbI3 surface, leading to significant etching of the MAPbI3 single crystal surface and disruption of the crystal lattice structure, thus severely hindering the heteroepitaxial growth process of the MAPbBr3 single crystal.

[0034] Figure 7 This is a cross-sectional view of a MAPbI3 single crystal two hours after epitaxial growth. The cross-sectional view clearly shows that at the MAPbI3 / MAPbBr3 interface, due to the dissolution effect of DMF, the MAPbI3 crystal arrangement becomes loose, no longer maintaining its original dense structure. This irregular crystal structure usually generates stress concentration internally, making the material more prone to cracking or fracturing under mechanical pressure, thus significantly affecting the processing performance and long-term stability of perovskite materials.

[0035] Comparative Example 2 The preparation method is as follows: 1. Dissolve 2.93g of lead acetate and 800µL of methylamine solution in 12ml of hydrobromic acid (HBr), and then place on a 70℃ hot plate and let stand for 12h to obtain the MAPbBr3 precursor solution.

[0036] 2. Place the MAPbI3 single crystal in the MAPbBr3 precursor solution prepared above and let it stand at 70°C for 20 minutes.

[0037] 3. Cool the MAPbBr3 precursor solution to 30℃ at a rate of 0.5℃ / min for epitaxial growth.

[0038] Depend on Figure 8 As can be seen from the optical micrographs of the crystal surface, under these epitaxial conditions, the crystallization quality of the single crystal epitaxy is similar to that of Examples 1 and 2. Figure 1 , Figure 3 The effects are significantly different.

[0039] Comparative Example 3 1. First, prepare a saturated acid solution: Dissolve 2.93g of lead acetate in 10ml of hydrobromic acid (HBr) solution to form the first saturated solution; slowly add 2ml of hydrobromic acid (HBr) solution dropwise to 800µL of methylamine solution to form the second mixed solution. Mix the first saturated solution and the second mixed solution in a 20ml glass bottle.

[0040] 2. Place the MAPbI3 single crystal in the saturated acidic solution of MAPbBr3 prepared above, and let it stand at 70°C for 20 minutes to form a transition layer on the surface of the MAPbI3 single crystal by displacement.

[0041] 3. Cool the saturated acidic solution of MAPbBr3 to 30℃ at a rate of 0.5℃ / min to carry out epitaxial growth.

[0042] Depend on Figure 9 As can be seen from the optical micrographs of the crystal surface, under these epitaxial conditions, the crystallization quality of the single crystal epitaxy is similar to that of Examples 1 and 2. Figure 1 , Figure 3 The effects are significantly different.

[0043] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they shall still fall within the protection scope of the present invention.

Claims

1. A method for perovskite single crystal hetero-epitaxial growth, the method comprising: The method comprises the following steps: S1: obtaining a saturated acid solution S101: dissolving a metal salt corresponding to a target halide perovskite in a hydrobromic acid solution to form a first saturated solution; S102: mixing the hydrobromic acid solution with an organic amine solution or a cesium salt to form a second mixed solution; S103: mixing the first saturated solution and the second mixed solution, and then standing and aging at a preset temperature to form a stable saturated acid solution system; wherein steps S101 and S102 are not in a specific order; S2: perovskite heteroepitaxy S201: immersing a substrate perovskite in the saturated acid solution of step S1, and performing an ion exchange reaction at a preset temperature to form a halogen gradient transition layer on the substrate perovskite; S202: using a cooling crystallization method to make the target halide perovskite directionally precipitate and epitaxially grow on the surface of the halogen gradient transition layer.

2. The method for perovskite single crystal hetero-epitaxial growth according to claim 1, wherein The temperature for standing and aging in step S103 is 60-90℃.

3. The method for perovskite single crystal hetero-epitaxial growth according to claim 1, wherein The time for standing and aging in step S103 is 12-24h.

4. The method for perovskite single crystal hetero-epitaxial growth according to claim 1, wherein The ion exchange reaction in step S201 is performed at 60-90℃ for 10-30min.

5. The method of perovskite single crystal hetero-epitaxial growth of claim 1, wherein, In step S202, the temperature is lowered at a rate of 0.5-5℃ / min to 20-30℃, the solubility of the target halide perovskite in the acid solution is reduced by lowering the temperature, the target halide perovskite directionally precipitates on the surface of the halogen gradient transition layer, and heteroepitaxy is achieved.

6. The method of perovskite single crystal hetero-epitaxial growth of claim 1, wherein, The organic amine is any one of methylamine, ethylamine, phenethylamine or n-butylamine.

7. The method of perovskite single crystal hetero-epitaxial growth of claim 1, wherein, The metal salt corresponding to the target halide perovskite is any one or a mixture of several of lead oxide, tin oxide, lead halide, tin halide, lead nitrate or lead acetate.

8. The method of perovskite single crystal hetero-epitaxial growth of claim 1, wherein, The substrate perovskite is a three-dimensional perovskite, a two-dimensional perovskite or an inorganic perovskite. The target halide perovskite is a material different from the halogen component on the surface of the substrate perovskite.

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