A copper indium selenide-based inorganic plastic van der Waals single crystal material, its preparation method and application

Abstract

The present invention relates to the field of semiconductor materials, and discloses a copper indium selenide-based inorganic plastic van der Waals single crystal material, a preparation method thereof, and an application. The chemical formula of the material is CuIn x Se y , where 3 < x < 10 and 5 < y < 16; it has a layered van der Waals single crystal structure. The preparation method includes: 1) Vacuum-sealing, heating to melt, and holding the temperature of Cu, In, and Se, and then cooling to obtain a polycrystalline rod; 2) Vertically placing the polycrystalline rod in a double-temperature zone vertical single crystal furnace, increasing the temperature from the bottom to the top, and then cooling to form a single crystal ingot; 3) Cleaving and cutting to obtain the copper indium selenide-based inorganic plastic van der Waals single crystal material. The present invention finds that for materials meeting the above conditions, the room-temperature plastic bending strain can reach 5-50%, and it can be bent, twisted, folded, and compressed within a thickness range of 100 μm - 100 mm without breaking, and the room-temperature conductivity can be maintained at 100 - 8000 S m ‑1 , and the conductivity increases with the increase of temperature.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor materials, and in particular to a copper indium selenide-based inorganic plastic van der Waals single crystal material, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid progress of modern technology, electronic products are continuously moving towards the development of flexibility, miniaturization, and even micro-miniaturization to break through the technical barriers that are difficult to overcome by traditional methods. In recent years, flexible electronic materials and devices have attracted increasing attention and emphasis from the academic and industrial circles at home and abroad. Their unique flexibility / ductility and efficient, low-cost manufacturing processes have shown broad and important application prospects in the fields of information, energy, medical care, national defense, etc., and are regarded as revolutionary electronic technologies in the future.

[0003] Different from traditional rigid silicon-based semiconductor electronic devices, flexible electronic devices should have the functions of being bendable / stretchable or wearable, which puts forward requirements for the flexibility and plasticity of the material itself. Most of the existing inorganic semiconductor materials have excellent electrical properties, but usually have intrinsic brittleness and poor mechanical processing and deformation capabilities; while polymer materials have good deformation capabilities, but poor semiconductor characteristics. Developing semiconductors with good flexibility and plasticity is expected to achieve the rapid development of the flexible electronics field.

[0004] In recent years, the discovery of intrinsically inorganic flexible and plastic semiconductors such as Ag2S and InSe has opened a new era of flexible electronic materials and devices. For example, at room temperature, Ag2S has a metal-like deformation ability and can be bent and twisted into different shapes without fracture. All the currently discovered inorganic flexible and plastic semiconductors are binary compounds. Ternary compounds are a class of material systems with rich structures, physical, and mechanical properties, and there should also be some intrinsically inorganic flexible and plastic semiconductors with similar abnormal mechanical properties, but there are almost no reports and studies at present.

[0005] Patent CN111403558A discloses a high-efficiency flexible laminated thin-film solar cell and a preparation method thereof. The copper indium selenide absorption layer is deposited on the surface of a flexible substrate by a three-step co-evaporation method, and finally a flexible laminated solar cell thin film is prepared. However, in this patent, the copper indium selenide absorption layer itself does not have sufficient flexibility, and it can only be deposited on the surface of a flexible substrate in a relatively thin (2-3 microns) form to achieve moderate bending. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a copper indium selenide-based inorganic plastic van der Waals single crystal material, a preparation method thereof, and an application thereof. First of all, the present invention discovers that the chemical formula is CuIn x Se y, a copper-indium-selenium-based inorganic plastic layered van der Waals single crystal material with 3 < x < 10 and 5 < y < 16 has excellent plasticity. Its room-temperature plastic bending strain can reach 5 - 50%, and it can be bent, twisted, folded, and compressed at room temperature within the range of 100 μm - 100 mm in thickness without fracture. Moreover, it is valuable that while the material has high plasticity, it does not affect its room-temperature electrical conductivity (100 - 8000 S m -1 ), and the electrical conductivity increases with the increase of temperature. Secondly, through strict control in many aspects such as element ratio and heat treatment process, the present invention successfully prepares a copper-indium-selenium-based inorganic plastic van der Waals single crystal material with the above properties.

[0007] The specific technical solution of the present invention is as follows:

[0008] In the first aspect, the present invention provides a copper-indium-selenium-based inorganic plastic van der Waals single crystal material with the chemical formula CuIn x Se y , 3 < x < 10, 5 < y < 16; and has a layered van der Waals single crystal structure.

[0009] The present invention discovers that a copper-indium-selenium-based inorganic plastic van der Waals single crystal material that simultaneously meets the above characteristics has excellent plasticity. Its room-temperature plastic bending strain can reach 5 - 50% (further preferably 10 - 30%), and it can be bent, twisted, folded, and compressed at room temperature within the range of 100 μm - 100 mm (further preferably 1 - 10 mm) in thickness without fracture. Moreover, it is valuable that while the material has high plasticity, it does not affect its room-temperature electrical conductivity (100 - 8000 S m -1 ), and the electrical conductivity increases with the increase of temperature.

[0010] Preferably, 5 ≤ x ≤ 9, 8 ≤ y ≤ 14; further preferably, x = 5, y = 8; or x = 6, y = 9.5; or x = 7, y = 11; or x = 8, y = 12.5.

[0011] The present invention discovers that the ratio of Cu, In, and Se has a certain influence on the plasticity of the finally obtained single crystal material; through experiments, the present invention further discovers that controlling the molar ratio of the three within the above range can not only successfully prepare a layered van der Waals single crystal material, but also have excellent plasticity and electrical conductivity.

[0012] In the second aspect, the present invention provides a preparation method of a copper-indium-selenium-based inorganic plastic van der Waals single crystal material, including: 1) Vacuum-sealing the elements of Cu, In, and Se in a quartz tube, heating to the melting temperature and holding for a certain time, and then cooling to obtain a polycrystalline rod.

[0013] 2) Vertically place the quartz tube containing the polycrystalline rod in a double-temperature-zone vertical single-crystal furnace. The temperature in the furnace cavity increases from the bottom to the top of the quartz tube. Control the furnace cavity to heat up, so that the temperature in the bottom area of the quartz tube is 20 - 100 °C above the melting temperature. Subsequently, control the furnace cavity to cool down, so that the temperature in the top area of the quartz tube is 20 - 100 °C below the melting temperature, and cool to room temperature to form a single-crystal ingot.

[0014] 3) Cleave and cut the single-crystal ingot to obtain a single-crystal block, namely the copper indium selenide-based inorganic plastic van der Waals single-crystal material.

[0015] In step 1), the present invention melts and cools Cu, In, and Se in a specific ratio to prepare a polycrystalline rod. In step 2), the polycrystalline rod is transformed into a single crystal. In this process, the polycrystalline rod is vertically placed in a vertical single-crystal furnace, and its temperature increases from bottom to top. First, the bottom temperature is raised to 20 - 100 °C above the melting temperature, and then cooled to 20 - 100 °C below the melting temperature, and cooled to room temperature to form a single-crystal ingot. The polycrystalline rod will melt into a liquid above the melting temperature. Under the condition of a certain temperature gradient, nucleation and crystallization first occur in the low-temperature area at the bottom, and then slowly grow from bottom to top along the solid-liquid interface, finally forming a single-crystal material with a single orientation. In step 3), the obtained single-crystal ingot is cleaved and cut to obtain the copper indium selenide-based inorganic plastic van der Waals single-crystal material. The room-temperature plastic bending strain of this copper indium selenide-based inorganic plastic van der Waals single-crystal material can reach 5 - 50%, and it can be bent, twisted, folded, and compressed at room temperature within the range of 100 μm - 100 mm in thickness without fracture. And valuably, while the material has high plasticity, it does not affect its room-temperature conductivity (100 - 8000 S m -1 ), and the conductivity increases with the increase of temperature.

[0016] Preferably, in step 2), the cooling rate is 0.5 - 10 °C / h.

[0017] The present invention finds that the cooling rate after melting in step 2) is crucial for the plasticity of the single-crystal material. The present invention further finds through experiments that by controlling the cooling rate within the above specific range (0.5 - 10 °C / h), a single-crystal material with high plasticity can be obtained. If the cooling rate is too fast, it will cause the melt to cool and solidify quickly, with many internal defects and disordered growth orientations in the material, and it is impossible to form a high-quality and large-size van der Waals single-crystal material.

[0018] Preferably, in steps 1) and 2), the heating rate is 20 - 200 °C / h; the cooling rate is 10 - 100 °C / h.

[0019] The heating and cooling rates in Step 1) and Step 2) also have a certain influence on whether single-crystal materials can be obtained and the crystal form and properties of the single-crystal materials. If the heating rate is too fast, it is easy to cause the material reaction to be too intense, resulting in the inability to obtain ideal polycrystalline or single-crystal materials; if the cooling rate is too fast, it is easy to cause the volume change of the single-crystal ingot material to be too fast, resulting in cracking of the single-crystal rod and reducing the crystal quality. If the heating and cooling rates are too slow, it will also affect the crystal properties and preparation efficiency. Finally, in the present invention, it is better to control the heating and cooling rates within the above specific ranges.

[0020] Preferably, in Step 2), the temperature difference between the bottom and the top of the quartz tube is 5-100 °C.

[0021] In Step 2), a certain temperature gradient is required during the single-crystal growth process to drive the nucleation and crystallization growth of the material, which is beneficial to the formation of van der Waals single crystals. If the temperature gradient is too small, the driving force for single-crystal growth is insufficient, resulting in slow crystal growth and disordered orientation. If the temperature gradient is too large, the driving force is too large, resulting in too fast nucleation speed and it is difficult to form high-quality large-size single-crystal materials.

[0022] Preferably, in Step 1), the purity of the Cu, In, and Se elemental substances is ≥99.9999%; the particle sizes of the Cu, In, and Se elemental substances are 1-3 mm.

[0023] Preferably, in Step 1), the melting temperature is 900-1200 °C; the heat preservation time is 0.5-20 h.

[0024] Preferably, in Step 1) and Step 2), the vacuum degree of the vacuum sealing is ≤5 Pa.

[0025] Preferably, in Step 3), the cleavage is to separate the crystal along the layered texture of the single-crystal growth to obtain a bright and flat single-crystal cleavage plane.

[0026] Preferably, in Step 3), the cutting is mechanical cutting perpendicular to the single-crystal cleavage plane.

[0027] In the third aspect, the present invention provides the application of the copper indium selenide-based inorganic plastic van der Waals single-crystal material obtained by the above preparation method in various flexible electronic devices, microelectronic devices, and flexible solar cells.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] (1) Through strict control in multiple aspects such as element ratio and heat treatment process, the present invention successfully prepared a copper indium selenide-based inorganic plastic van der Waals single crystal material, whose room temperature plastic bending strain can reach 5 - 50%, and it can be bent, twisted, folded, and compressed at room temperature within the range of 100 μm - 100 mm in thickness without fracture. The maximum bendable thickness at room temperature > 2 mm, and at the same time, it can maintain the room temperature conductivity at 100 - 8000 S m -1 , and the conductivity increases with the increase of temperature.

[0030] (2) The preparation method and required equipment of the present invention are relatively simple, with good controllability and repeatability, and are suitable for industrial promotion.

[0031] (3) The copper indium selenide-based inorganic plastic van der Waals single crystal material prepared by the present invention is expected to be applied in the fields of flexible electronic devices, microelectronic devices, flexible solar cells, etc. Description of the Drawings

[0032] Figure 1 is a photograph of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0033] Figure 2 is the XRD pattern of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0034] Figure 3 is a scanning electron microscope photograph of the cleavage plane of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0035] Figure 4 is a scanning electron microscope photograph of the fracture perpendicular to the cleavage plane of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0036] Figure 5 is a photograph of the bending deformation of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0037] Figure 6 is the three-point bending stress-strain curve of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0038] Figure 7 is the compression stress-strain curve of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0039] Figure 8It is the graph of the conductivity of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention varying with temperature.

[0040] Figure 9 It is the graph of the Seebeck coefficient of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention varying with temperature.

[0041] Figure 10 It is the graph of the thermoelectric power factor of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention varying with temperature. Specific embodiments

[0042] The present invention will be further described below in conjunction with embodiments.

[0043] General embodiment

[0044] First, a preparation method of a copper indium selenide-based inorganic plastic van der Waals single crystal material specifically includes the following steps:

[0045] 1) Vacuum-seal the elemental substances of Cu, In, and Se in a quartz tube, heat up to the melting temperature and keep it warm, and then cool to obtain a polycrystalline rod. Among them, the molar ratio of Cu, In, and Se is 1:x:y, and 3 < x < 10, 5 < y < 16.

[0046] In some specific implementation cases, 5 ≤ x ≤ 9, 8 ≤ y ≤ 14; in some more preferred implementation cases, x = 5, y = 8; or x = 6, y = 9.5; or x = 7, y = 11; or x = 8, y = 12.5.

[0047] In some specific implementation cases, the purity of the elemental substances of Cu, In, and Se is ≥99.9999%; the particle size of the elemental substances of Cu, In, and Se is 1 - 3 mm.

[0048] In some specific implementation cases, the heating rate is 20 - 200 °C / h; the cooling rate is 10 - 100 °C / h.

[0049] In some specific implementation cases, the melting temperature is 900 - 1200 °C; the holding time is 0.5 - 20 h.

[0050] In some specific implementation cases, the vacuum degree of the vacuum seal is ≤5 Pa.

[0051] 2) Vertically place the quartz tube containing the polycrystalline rod in a double-temperature-zone vertical single crystal furnace. The temperature in the furnace cavity increases from the bottom to the top of the quartz tube. Control the furnace cavity to heat up so that the temperature in the bottom area of the quartz tube is 20 - 100 °C above the melting temperature. Subsequently, control the furnace cavity to cool down so that the temperature in the top area of the quartz tube is 20 - 100 °C below the melting temperature, and cool it to room temperature to form a single crystal ingot.

[0052] In some specific implementation cases, the heating rate is 20 - 200 °C / h; the slow cooling rate is 0.5 - 10 °C / h. The cooling rate is 10 - 100 °C / h.

[0053] In some specific implementation cases, the temperature difference between the bottom and the top of the quartz tube is 5 - 100 °C.

[0054] In some specific implementation cases, the vacuum degree of the vacuum seal is ≤5 Pa.

[0055] 3) Cleave and cut the single crystal ingot to obtain single crystal blocks, namely copper indium selenide-based inorganic plastic van der Waals single crystal materials.

[0056] In some specific implementation cases, the cleavage is to separate the crystal along the layered texture of the single crystal growth to obtain a bright and flat single crystal cleavage plane.

[0057] In some specific implementation cases, the cutting is mechanical cutting along a direction perpendicular to the single crystal cleavage plane.

[0058] Secondly, the copper indium selenide-based inorganic plastic van der Waals single crystal material obtained by the above preparation method has a layered van der Waals single crystal structure, and its chemical formula is CuIn x Se y , 3 < x < 10, 5 < y < 16; the thickness is 100 μm - 100 mm (more preferably 1 - 10 mm), the room temperature conductivity is 100 - 8000 S m -1 , and the conductivity increases with the increase of temperature; the room temperature plastic bending strain is 5 - 50% (more preferably 15 - 30%).

[0059] In some preferred implementation cases, 5 ≤ x ≤ 9, 8 ≤ y ≤ 14; most preferably, x = 5, y = 8; or x = 6, y = 9.5; or x = 7, y = 11; or x = 8, y = 12.5.

[0060] Finally, the application of the copper indium selenide-based inorganic plastic van der Waals single crystal material obtained by the above preparation method in various flexible electronic devices, microelectronic devices and flexible solar cells.

[0061] Specific examples and comparative examples (1) Effects of different Cu, In, Se molar ratios on the crystal form and various properties of single crystal materials

[0062] Examples 1-3 and Comparative Examples 1-3

[0063] (1) Preparation of polycrystalline rod: Using Cu grains (purity 99.9999%, particle size 1-3 mm), In grains (purity 99.9999%, particle size 1-3 mm), and Se grains (purity 99.9999%, particle size 1-3 mm) as the initial raw materials, weigh a total mass of 20 g according to the stoichiometric molar ratio (see Table 1 for details). Vacuum-seal the initial raw materials in a quartz tube (φ10 mm, vacuum degree ≤ 5 Pa), and place it in a muffle furnace at 50 °C / h -1 Heat up to 1100 °C and hold for 12 h to completely melt the initial raw materials. Then cool down at 50 °C / h -1 to room temperature to obtain a polycrystalline rod.

[0064] (2) Preparation of single-crystal ingot: Vacuum-seal the polycrystalline rod in a quartz tube, with a vacuum degree ≤ 5 Pa, and place it vertically in a double-temperature-zone vertical single-crystal furnace; heat the furnace cavity at a rate of 50 °C / h -1 so that the low-temperature zone (bottom of the quartz tube) is 1150 °C (the temperature difference between the low-temperature zone and the high-temperature zone is 10 °C); then slowly cool down at a rate of 2 °C / h -1 so that the high-temperature zone (top of the quartz tube) is 1050 °C (the temperature difference between the low-temperature zone and the high-temperature zone is 10 °C), and then cool down to room temperature at 50 °C / h -1 to form a single-crystal ingot.

[0065] (3) Preparation of single-crystal block: Finally, separate the crystal along the texture of single-crystal growth to obtain a bright and flat single-crystal cleavage plane, and mechanically cut perpendicular to the single-crystal cleavage plane to obtain a single-crystal block, namely the copper indium selenide-based inorganic single-crystal material.

[0066] The properties of the single-crystal materials obtained in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0067] Table 1: Plastic properties and electrical conductivity of the single-crystal materials obtained in Examples 1-3 and Comparative Examples 1-3

[0068]

[0069] Among them: The test methods for room-temperature bending strain and maximum bendable thickness are: three-point bending mechanical test; the test method for room-temperature conductivity is: using a resistivity and Seebeck coefficient measurement system for testing.

[0070] It can be seen from the data comparison in Table 1 that when the molar ratios of Cu, In, and Se are 1:1:2 (Comparative Example 1), 1:3:5 (Comparative Example 2), and 1:12:18 (Comparative Example 3) respectively, although the copper indium selenide-based single crystal material can finally be prepared by the above preparation process, the van der Waals single crystal cannot be successfully formed under the above molar ratios, and the finally obtained copper indium selenide-based single crystal material basically does not have plasticity. In contrast, when the molar ratios of Cu, In, and Se are 1:5:8 (Example 1), 1:7:11 (Example 2), and 1:8:12.5 (Example 3) respectively, the copper indium selenide-based van der Waals single crystal material with a layered structure can be successfully prepared by the above preparation process, and the maximum bendable thickness of the obtained single crystal material is greater than 1.5 mm at room temperature, the room temperature plastic bending strain is greater than 15%, and it has an ideal room temperature conductivity at the same time.

[0071] Specifically, Figure 1 is a photograph of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention; Figure 2 is an XRD pattern of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention;

[0072] Figure 3 is a scanning electron microscope photograph of the cleavage plane of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention; Figure 4 is a scanning electron microscope photograph of the fracture perpendicular to the cleavage plane of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0073] Figure 5 is a photograph of the bending deformation of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention.

[0074] Figure 6 is a three-point bending stress-strain curve of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention. It can be observed that the maximum bending strength of the sample is 11.5 MPa, and its strain exceeds 17%, indicating that the material can undergo large bending deformation without obvious brittle fracture and has good plastic deformation ability.

[0075] Figure 7 is a compressive stress-strain curve of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention. It can be observed that the maximum compressive strength of the sample is 72 MPa, and its strain exceeds 20%, indicating that the material can be greatly compressed without obvious brittle shear failure and has good plastic deformation ability.

[0076] Figure 8 It is the graph of the conductivity of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention varying with temperature. It can be observed that the conductivity of this sample increases with the increase of temperature, showing semiconductor conduction behavior. When the temperature is 300K, the conductivity of this material is 1.879×10 2 S m -1 ; when the temperature is 700K, the conductivity is 1.138×10 3 Sm -1 . Therefore, this material is a semiconductor material with good conductivity.

[0077] Figure 9 It is the graph of the Seebeck coefficient of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention varying with temperature. It can be observed that the Seebeck coefficient of this sample is negative in the test temperature range, indicating that this material is an n-type semiconductor. And the absolute value of it first increases and then decreases with the increase of temperature. When the temperature is 300K, the Seebeck of this material is -478μVK -1 ; when the temperature is 700K, the Seebeck coefficient is -373μV K -1 .

[0078] Figure 10 It is the graph of the thermoelectric power factor of the copper indium selenide-based inorganic plastic van der Waals single crystal material CuIn5Se8 obtained in Example 1 of the present invention varying with temperature. It can be observed that the power factor of this sample increases with the increase of temperature. When the temperature is 700K, the power factor is 1.6μw cm -1 K -2 , indicating that this material has certain application prospects in the thermoelectric field.

[0079] (2) Influence of different cooling rates during single crystal growth on the properties of single crystal materials

[0080] Examples 4 - 6 and Comparative Examples 4 - 5

[0081] (1) Preparation of polycrystalline rods: Using Cu grains (purity 99.9999%, particle size 1 - 3mm), In grains (purity 99.9999%, particle size 1 - 3mm) and Se grains (purity 99.9999%, particle size 1 - 3mm) as the initial raw materials, weighing a total mass of 20g according to the stoichiometric molar ratio of 1:5:8. Vacuum seal the initial raw materials in a (φ10mm quartz tube, vacuum degree ≤ 5Pa), and place it in a muffle furnace to heat up to 1100℃ at 50℃h -1 and keep it warm for 12h to make all the initial raw materials melt. Then cool it to room temperature at 50℃h -1 to obtain polycrystalline rods.

[0082] (2) Preparation of crystal ingots: The polycrystalline rod is vacuum-sealed in a quartz tube with a vacuum degree ≤ 5 Pa and placed vertically in a double-temperature vertical single crystal furnace; the furnace cavity is heated at a rate of 50 °C / h -1 so that the low-temperature zone (the bottom of the quartz tube) is at 1150 °C (the temperature difference between the low-temperature zone and the high-temperature zone is 10 °C); then it is slowly cooled at a rate of 0.5 - 50 °C / h -1 (see Table 2 for details) so that the high-temperature zone (the top of the quartz tube) is at 1050 °C (the temperature difference between the low-temperature zone and the high-temperature zone is 50 °C), and then it is cooled to room temperature at a rate of 50 °C / h -1 to form a crystal ingot.

[0083] (3) Preparation of crystal blocks: Finally, the crystal is separated along the crystal growth texture to obtain a bright and flat cleavage plane, and then mechanically cut perpendicular to the cleavage plane to obtain crystal blocks, namely copper indium selenide-based crystal materials.

[0084] The crystal forms and various properties of the crystal materials obtained in the above Examples 4 - 6 and Comparative Examples 4 - 5 are shown in Table 2.

[0085] Table 2: Plastic properties and electrical conductivity of the crystal materials obtained in Examples 4 - 6 and Comparative Examples 4 - 5

[0086]

[0087] It can be seen from the data comparison in Table 2 that during the process of polycrystalline to single crystal conversion in step (2), different cooling rates will have a significant impact on the crystal type and the properties of the obtained materials. Specifically, within the range of relatively fast cooling rates (20 °C / h in Comparative Example 4 -1 , 50 °C / h in Comparative Example 5 -1 ), although the copper indium selenide-based material can ultimately be obtained through the above preparation process, due to the too fast cooling rate, the nucleation and crystallization rates are too fast, and it is easy to form polycrystals with small grain sizes and disordered orientations and thus do not have plasticity. In contrast, within the range of relatively slow cooling rates (0.5 °C / h in Example 4 -1 , 5 °C / h in Example 5 -1 , 10 °C / h in Example 6 -1 ), the copper indium selenide-based van der Waals single crystal material can be successfully obtained through the above preparation process, and the maximum bendable thickness of the obtained single crystal material at room temperature is greater than 2.0 mm, the room temperature plastic bending strain is greater than 15%, and it also has an ideal room temperature electrical conductivity.

[0088] (III) Influence of different temperature differences between the top and bottom of the quartz tube in the furnace cavity on the crystal form and various properties of the material

[0089] Examples 7 - 8

[0090] (1) Preparation of polycrystalline rod: Cu grains (purity 99.9999%, particle size 1 - 3 mm), In grains (purity 99.9999%, particle size 1 - 3 mm), and Se grains (purity 99.9999%, particle size 1 - 3 mm) were used as starting materials. A total mass of 20 g was weighed according to the stoichiometric molar ratio of 1:5:8. The starting materials were vacuum-sealed in a (φ10 mm quartz tube, with a vacuum degree ≤ 5 Pa) and placed in a muffle furnace at 50 °C / h -1 Heated to 1100 °C and held for 12 h to completely melt the starting materials. Subsequently, at 50 °C / h -1 Cooled to room temperature to obtain a polycrystalline rod.

[0091] (2) Preparation of single-crystal ingot: The polycrystalline rod was vacuum-sealed in a quartz tube, with a vacuum degree ≤ 5 Pa, and vertically placed in a two-temperature-zone vertical single-crystal furnace; the furnace chamber was heated at a rate of 50 °C / h -1 so that the low-temperature zone (bottom of the quartz tube) was 1150 °C (the temperature difference between the low-temperature zone and the high-temperature zone was 5 - 20 °C, see Table 3 for details); subsequently, it was slowly cooled at a rate of 2 °C / h -1 so that the high-temperature zone (top of the quartz tube) was 1050 °C, and then cooled to room temperature at 50 °C / h -1 to form a single-crystal ingot.

[0092] (3) Preparation of single-crystal block: Finally, the crystal was separated along the layered texture of single-crystal growth to obtain a bright and flat single-crystal cleavage plane, and mechanically cut perpendicular to the single-crystal cleavage plane to obtain a single-crystal block, namely the copper indium selenide-based single-crystal material.

[0093] Comparative Example 6

[0094] (1) Cu grains (purity 99.9999%, particle size 1 - 3 mm), In grains (purity 99.9999%, particle size 1 - 3 mm), and Se grains (purity 99.9999%, particle size 1 - 3 mm) were used as starting materials. A total mass of 20 g was weighed according to the stoichiometric molar ratio of 1:5:8. The starting materials were vacuum-sealed in a (φ10 mm quartz tube, with a vacuum degree ≤ 5 Pa) and placed in a muffle furnace at 50 °C / h -1 Heated to 1100 °C and held for 12 h to completely melt the starting materials. Subsequently, at 50 °C / h -1 Cooled to room temperature to obtain a polycrystalline rod.

[0095] (2) The polycrystalline rod was vacuum-sealed in a quartz tube, with a vacuum degree ≤ 5 Pa, and vertically placed in a two-temperature-zone vertical single-crystal furnace; the furnace chamber was heated at a rate of 50 °C / h -1 so that the low-temperature zone (bottom of the quartz tube) was 1150 °C (the temperature difference between the low-temperature zone and the high-temperature zone was 0 °C, see Table 3 for details); subsequently, at 2 °C / h -1Reduce the temperature at a rate of, making the high-temperature area (the top of the quartz tube) 1050 °C, and then at 50 °C / h -1 Cool to room temperature to form an ingot.

[0096] (3) It is found that the ingot is not single crystal and there is no obvious separable layer.

[0097] The properties of the crystal materials obtained in the above Examples 7-8 and Comparative Example 6 are shown in Table 3.

[0098] Table 3: Plastic properties and electrical conductivity of the crystal materials obtained in Examples 1-3 and Comparative Examples 1-3

[0099]

[0100] It can be seen from the data comparison in Table 3 that during the process of polycrystalline to single crystal in step (2), different temperature differences in the furnace cavity (the bottom and top of the quartz tube) will also have a significant impact on the crystal type and the properties of the obtained material. Specifically, in Comparative Example 6, the temperatures at the bottom and top of the quartz tube were set to be the same, that is, no temperature difference was set. Under this condition, it was finally found that a copper indium selenide-based single crystal material could not be formed, and the obtained material basically did not have plasticity. In contrast, under the temperature difference conditions of 5 °C (Example 7) and 20 °C (Example 8), a copper indium selenide-based van der Waals single crystal material can be successfully prepared by the above preparation process. And the maximum bendable thickness of the obtained single crystal material at room temperature is greater than 2.0 mm, the room temperature plastic bending strain is greater than 15%, and at the same time it has an ideal room temperature conductivity.

[0101] In summary, through strict control in many aspects such as the element ratio control of copper indium selenide and the heat treatment process, the present invention has successfully prepared a copper indium selenide-based inorganic plastic van der Waals single crystal material with excellent plasticity. This material has a layered van der Waals single crystal structure, and its chemical formula is CuIn x Se y , 3 < x < 10, 5 < y < 16 (preferably: 5 ≤ x ≤ 9, 8 ≤ y ≤ 14; more preferably: x = 5, y = 8; or x = 6, y = 9.5; or x = 7, y = 11; or x = 8, y = 12.5). The room temperature plastic bending strain of this material can reach 5-50%, and it can be bent, twisted, folded, and compressed at room temperature within the range of 100 μm - 100 mm in thickness without fracture. And valuably, while the material has high plasticity, it does not affect its room temperature conductivity (100 - 8000 S / m -1 ), and the conductivity decreases with the increase of temperature. The copper indium selenide-based inorganic plastic van der Waals single crystal material prepared by the present invention is expected to be applied in the fields of flexible electronic devices, microelectronic devices, and flexible solar cells. The preparation method and the required equipment of the present invention are relatively simple, with good controllability and repeatability, and are suitable for industrial promotion.

[0102] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0103] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of a copper indium selenide-based inorganic plastic van der Waals single crystal material, characterized in that Comprising: 1) Vacuum-sealing the elemental substances of Cu, In, and Se in a quartz tube, heating to the melting temperature and holding for a certain time, then cooling to obtain a polycrystalline rod; 2) Vertically placing the quartz tube containing the polycrystalline rod in a double-temperature-zone vertical single crystal furnace, where the temperature in the furnace cavity increases from the bottom to the top of the quartz tube with a temperature difference of 5 - 100 °C; controlling the furnace cavity to heat up so that the temperature in the bottom region of the quartz tube is 20 - 100 °C above the melting temperature, and then controlling the furnace cavity to cool down so that the temperature in the top region of the quartz tube is 20 - 100 °C below the melting temperature, and cooling to room temperature to form a single crystal ingot; In steps 1) and 2), the heating rate is 20 - 200 °C / h; the cooling rate is 10 - 100 °C / h; in step 2), the cooling rate is 0.5 - 10 °C / h; 3) Cleave and cut the single crystal ingot to obtain a copper indium selenide-based inorganic plastic van der Waals single crystal material with a layered van der Waals single crystal structure, with the chemical formula CuIn x Se y , where x = 5, y = 8; or x = 7, y = 11; or x = 8, y = 12.5; the material has a thickness of 100 μm - 100 mm, and the room temperature plastic bending strain is 5 - 50%; the room temperature conductivity is 100 - 8000 S m -1 , and the conductivity increases with increasing temperature.

2. The preparation method according to claim 1, characterized in that: In step 1), the melting temperature is 900 - 1200 °C; the holding time is 0.5 - 20 h.

3. The preparation method according to claim 1, characterized in that: In step 3), the cleavage is to separate the crystal along the layered texture of single crystal growth to obtain a bright and flat single crystal cleavage plane.

4. The preparation method according to claim 1, characterized in that: In step 3), the cutting is mechanical cutting along a direction perpendicular to the single crystal cleavage plane.

5. Application of the copper indium selenide-based inorganic plastic van der Waals single crystal material obtained by the preparation method according to claim 1 in flexible electronic devices, microelectronic devices, or flexible solar cells.

6. A method for improving the plasticity of copper indium selenide-based van der Waals single crystal materials, characterized in that Comprising: 1) Vacuum-sealing the elemental substances of Cu, In, and Se in a quartz tube, heating to the melting temperature and holding for a certain time, then cooling to obtain a polycrystalline rod; 2) Vertically placing the quartz tube containing the polycrystalline rod in a double-temperature-zone vertical single crystal furnace, where the temperature in the furnace cavity increases from the bottom to the top of the quartz tube with a temperature difference of 5 - 100 °C; controlling the furnace cavity to heat up so that the temperature in the bottom region of the quartz tube is 20 - 100 °C above the melting temperature, and then controlling the furnace cavity to cool down so that the temperature in the top region of the quartz tube is 20 - 100 °C below the melting temperature, and cooling to room temperature to form a single crystal ingot; In steps 1) and 2), the heating rate is 20 - 200 °C / h; the cooling rate is 10 - 100 °C / h; in step 2), the cooling rate is 0.5 - 10 °C / h; 3) Cleave and cut the single crystal ingot to obtain a copper indium selenide-based inorganic plastic van der Waals single crystal material with a layered van der Waals single crystal structure, and the chemical formula is CuIn x Se y , where x = 5, y = 8; or x = 7, y = 11; or x = 8, y = 12.5; the material thickness is 100 μm - 100 mm, and the room temperature plastic bending strain is 5 - 50%; the room temperature conductivity is 100 - 8000 S m -1 , and the conductivity increases with the increase of temperature.

7. The method according to claim 6, wherein: In step 1), the melting temperature is 900 - 1200 °C; the holding time is 0.5 - 20 h.

8. The method according to claim 6, characterized in that: In step 3), the cleavage is to separate the crystal along the layered texture of single crystal growth to obtain a bright and flat single crystal cleavage plane.

9. The method according to claim 6, characterized in that: In step 3), the cutting is mechanical cutting along a direction perpendicular to the single crystal cleavage plane.

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