A method for growing an inch-level full-inorganic CsPbBr3 single crystal by VGF method

Abstract

The application provides a method for growing an inch-level full-inorganic CsPbBr3 single crystal by a VGF method, and belongs to the technical field of crystal growth. The application provides a preparation method for an inch-level full-inorganic perovskite single crystal, which comprises the following steps: taking CsPbBr3 polycrystal to perform impurity removal pretreatment to obtain a polycrystal precursor; placing the polycrystal precursor in an ampoule, heating to 100-300 DEG C under the condition that the vacuum degree is 10 ‑5 -10 ‑2 Pa and keeping for 1-8 h, and sealing the top end of the ampoule; performing segmented heating on the ampoule and then keeping, so that the polycrystal precursor is fully melted; and after the keeping is finished, gradiently cooling to room temperature to obtain an inch-level full-inorganic CsPbBr3 single crystal. The VGF method is adopted, the VGF furnace has good heat preservation effect, the internal temperature gradient is uniform, which is more conducive to improving the uniformity of the crystal, and can prevent cracks in the crystal, and is conducive to the preparation of a large-size single crystal.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of crystal growth, and particularly relates to a method for growing an inch-level full-inorganic CsPbBr3 single crystal by a VGF method. BACKGROUND

[0002] With the development of optoelectronic information technology, the application range of high-energy radiation detection is gradually expanding, and the application demand is increasing day by day. The semiconductor detection materials represented by silicon and germanium gradually cannot meet the needs of technological development. As the core material of high-energy radiation detectors, semiconductor single crystals need to have a large size and high crystalline quality. In view of the development requirements of high-energy radiation detectors, the detection materials need to meet several characteristics at the same time: ① high average atomic number; ② high resistivity; ③ appropriate band gap; ④ large carrier mobility-lifetime product, as shown in Table 1.

[0003] Table 1 Requirements of semiconductor materials

[0004]

[0005] Recent studies have shown that CsPbBr3 single crystals have many unique properties, such as large light absorption coefficient, large atomic number, high resistivity, large and balanced migration-lifetime product, and appropriate band gap, which determine that CsPbBr3 is a new ideal material for preparing high-energy radiation detectors.

[0006] At present, the growth of CsPbBr3 single crystals mainly includes solution method and melt method. However, the growth of CsPbBr3 single crystals still faces many difficulties and challenges such as small crystal size, easy cracking of crystal, low crystal transmittance, etc.

[0007] 1) The solution method is to dissolve PbBr2 and CsBr powders in a solvent according to a certain proportion, and then reduce the solubility by changing the temperature, so as to precipitate the crystal and achieve the effect of growing single crystal. However, it is difficult to obtain large-size single crystals by the solution method, so it cannot meet the industrialization needs of high-energy radiation detectors.

[0008] 2) The melt method mainly includes VB method, VGF method, etc. This method synthesizes single crystals by melting the polycrystalline precursor above the melting point and then recrystallizing the crystal by cooling.

[0009] ① The VB method has a constant temperature field, but since the VB growth process is completed by the movement of the crystal itself, mechanical vibration is inevitably caused, which leads to irregular fluctuations of the crystal growth interface, resulting in defects in the crystal and reducing the quality of the crystal.

[0010] The VGF method belongs to one of melt methods, and compared with the VB furnace, the VGF furnace has better heat preservation, and the method fixes the crystal and completes the crystal growth by relying on the change of the temperature gradient in the furnace, and there is no report about the growth of the inch-level all-inorganic CsPbBr3 single crystal by the VGF method.

[0011] Compared with the single crystal silicon (Si), high-purity germanium (HPGe) and other semiconductors commonly used for high-energy ray detection, the CsPbBr3 has a lower melting point and solidification point, and for the commercial application requirement, the CsPbBr3 is more suitable for using the melt method. At present, the crystal diameter grown by the melt method used by various research groups at home and abroad is basically about 10 mm, and the maximum is 30 mm, and all of them use 5N PbBr2 and CsBr as raw materials. The single crystal preparation cost of various research groups is high, and still in the laboratory research and development stage, and the size of the prepared crystal is basically difficult to meet the industrialization development requirement of the high-energy ray detector. Therefore, it is of great significance to obtain high-quality single crystal with high light transmittance, no crack and low defect density. SUMMARY

[0012] Therefore, the application aims to provide a method for growing inch-level all-inorganic CsPbBr3 single crystal.

[0013] To achieve the above-mentioned purpose, in a first aspect, the application provides a method for growing inch-level all-inorganic CsPbBr3 single crystal, comprising the following steps:

[0014] Step 1) taking the CsPbBr3 polycrystal for impurity removal pretreatment to obtain a polycrystal precursor;

[0015] Step 2) loading the pretreated polycrystal precursor into a quartz ampoule, after vacuumizing, heating and sealing, placing the ampoule in a crystal growth cavity, inserting 4-6 temperature measuring thermocouples at a specific position and fixing, and covering the top with a heat preservation cover;

[0016] Step 3) segmentally heating the crystal growth cavity and then heat preserving to make the polycrystal precursor fully melt, and then gradiently cooling to room temperature to obtain the inch-level all-inorganic CsPbBr3 single crystal;

[0017] The crystal growth cavity in step 3) is a four-temperature-zone VGF furnace, which is composed of a first heating zone, a second heating zone, a third heating zone and a fourth heating zone from bottom to top;

[0018] The step 3) is divided into three stages: the first stage is 2-6 h, and four heating zones are simultaneously heated from room temperature to 300-350℃; the second stage is 1-3 h, and the first heating zone is heated to 300-400℃, the second heating zone is heated to 400-500℃, the third heating zone and the fourth heating zone are simultaneously heated to 500-600℃; the third stage is 1-3 h, and the first heating zone is heated to 450-550℃, the second heating zone is heated to 500-600℃, the third heating zone and the fourth heating zone are simultaneously heated to 600-650℃; the temperature of the VGF furnace is increased by a temperature gradient of 2-10℃ / cm from bottom to top;

[0019] The holding time in the step 3) is 15-30 h;

[0020] The gradient cooling in the step 3) is divided into three stages: the first stage is 20-50 h, and the whole VGF furnace is simultaneously cooled from the third stage heating temperature to 150-180℃, wherein the cooling rate of the third and fourth heating zones is greater than that of the first and second heating zones, so as to reduce the temperature gradient in the VGF furnace; the second stage is 10-50 h, and each heating zone is simultaneously cooled to 60-70℃; the third stage is 4-8 h, and each heating zone is simultaneously cooled to room temperature.

[0021] Preferably, in the step 1), the CsPbBr3 polycrystal is prepared by using 2N PbBr2 and CsBr powders as raw materials; after the CsPbBr3 polycrystal is prepared, the CsPbBr3 polycrystal is impurity-removed 2-4 times according to the impurity content.

[0022] Preferably, the specific preparation steps of the CsPbBr3 polycrystal are as follows: PbBr2 and CsBr powders are respectively placed in two crucibles and heated to 180-260℃, vacuumized for 10 -5 ~10 -2 Pa, and dried for 1-3 h;

[0023] The dried PbBr2 and CsBr powders are weighed according to a molar ratio of 1:1 and mixed in a mortar, and are ground for 1-2 h; after the white PbBr2 and CsBr mixed powders are ground into orange-yellow CsPbBr3 powders, the CsPbBr3 powders are loaded into an ampoule, vacuumized, heated, and sealed; the ampoule is placed in a VGF furnace, heated to 580-640℃ within 3-6 h, and kept for 15-30 h; finally, the ampoule is cooled to room temperature within 40-60 h, and the CsPbBr3 polycrystal is taken out.

[0024] As preferred, the specific step of removing impurities of the CsPbBr3 polycrystal is: removing impurities on the surface and tail end of the CsPbBr3 polycrystal; then drying it in an ultra-clean cabinet; loading the treated CsPbBr3 polycrystal into an ampoule, vacuumizing, heating, and sealing the tube; loading the ampoule into a crystal growth cavity, inserting 4-6 temperature measuring thermocouples at specific positions and fixing them, then covering the top with a heat preservation cover; heating the furnace body to 560-620 DEG C within 6-10 h, keeping for 10-20 h; and cooling the ampoule to room temperature within 40-100 h, and taking out the purified CsPbBr3 polycrystal.

[0025] As preferred, the step of removing impurities in step 1) is: polishing the CsPbBr3 polycrystal at both ends and the impurities with darker color on the surface with 500-3000 mesh sandpaper, then ultrasonic cleaning in anhydrous ethanol in an ultrasonic cleaner for 1-2 h, and finally placing the crystal in an ultra-clean cabinet to volatilize the anhydrous ethanol on the surface.

[0026] As preferred, the inner diameter of the quartz ampoule is 25-65 mm, the wall thickness is 2-4 mm, the sharp end of the ampoule is provided with a 15-25 DEG conical angle, and the length of the shoulder area is 8-15 mm.

[0027] As preferred, the heating temperature in step 2) is 160-300 DEG C, the time is 2-3 h; the vacuum degree of vacuumizing is 10 -5 ~10 -2 Pa, the time is 1-8 h; the sealing method is sealed with hydrogen-oxygen flame; and the heating and vacuumizing are carried out simultaneously.

[0028] As preferred, the experimental apparatus needs to be cleaned before each step, and the specific steps are: first washing with ultrapure water to remove large impurities, then soaking the washed apparatus in a mixed solution of hydrochloric acid and sulfuric acid for 10-30 min, and finally washing the apparatus with ultrapure water and methanol in sequence to remove the mixed solution of hydrochloric acid and sulfuric acid.

[0029] As preferred, the steps of cleaning the experimental apparatus, loading the furnace, and treating the crystal are all carried out in an ultra-clean room with a cleanliness of less than 10 ppm.

[0030] The beneficial effects of the present application at least include:

[0031] 1. The present application adopts VGF method, the VGF furnace has good heat preservation effect, the internal temperature gradient is uniform, which is more conducive to improving the uniformity of the crystal, and can prevent cracks in the crystal, which is conducive to the preparation of large-size single crystals.

[0032] 2. The VGF furnace temperature control mentioned in the application is stable, and the temperature of each part of the crystal can be detected at any time by using the temperature measuring thermocouple, and the single crystal growth control temperature parameter is adjusted in time according to the temperature feedback, so that the success rate of single crystal preparation is greatly improved.

[0033] 3. The application uses the treated 2N high-quality CsPbBr3 polycrystal as the precursor, has low experimental cost and small experimental loss, and the equipment is simple, thereby reducing the single crystal preparation cost. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the VGF furnace;

[0035] Figure 2 It is a schematic diagram of the CsPbBr3 single crystal grown in Example 1;

[0036] Figure 3 It is a crystal XRD diagram of the crystal grown in Example 1;

[0037] Figure 4 It is a crystal transmission spectrum diagram of the crystal grown in Example 1;

[0038] Figure 5 It is a schematic diagram of the CsPbBr3 single crystal grown in Example 2;

[0039] Figure 6 It is a schematic diagram of the CsPbBr3 crystal grown in Example 3;

[0040] Figure 7 It is a schematic diagram of the CsPbBr3 crystal grown in Comparative Example 1;

[0041] Figure 8 It is a schematic diagram of the CsPbBr3 crystal grown in Comparative Example 2;

[0042] Figure 9 It is a schematic diagram of the CsPbBr3 crystal grown in Comparative Example 3.

[0043] Wherein: 1. First heating zone; 2. Second heating zone; 3. Third heating zone; 4. Fourth heating zone; 5. Temperature measuring thermocouple Tc1; 6. Temperature measuring thermocouple Tc2; 7. Temperature measuring thermocouple Tc3; 8. Temperature measuring thermocouple Tc4; 9. Heat preservation cover; 10. Support pipe; 11. CsPbBr3 single crystal. DETAILED DESCRIPTION

[0044] Now, various exemplary embodiments of the application will be described in detail, which should not be considered as limiting the application, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the application.

[0045] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. In addition, where a range of values is provided, it is understood that each intervening value, to the upper and lower limit of the range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges can independently be included or excluded in the range.

[0046] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application. All documents mentioned herein are incorporated by reference to disclose and describe the methods and / or materials in connection with which the documents are cited. In case of conflict, the present specification will control.

[0047] Various modifications and changes can be made to the specific embodiments of the present application described herein without departing from the scope or spirit of the application. Other embodiments of the application will be apparent to those of ordinary skill in the art from the description and examples herein. The description and examples are illustrative only.

[0048] As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", "contains", "containing", or variations thereof, are intended to be open-ended terms that mean including, but not limited to.

[0049] The "room temperature" and "normal temperature" described in the present application are 25±2℃, unless otherwise specified.

[0050] The preparation of large-size CsPbBr3 single crystals is carried out using a four-zone VGF furnace, which is composed of a first heating zone, a second heating zone, a third heating zone and a fourth heating zone from bottom to top, as shown in the structure of Figure 1 The crystal growth crucible is a transparent quartz ampoule with an inner diameter of 2 inches and a wall thickness of 3 mm. The tip of the ampoule is provided with a 15-25° taper angle. The length of the shoulder zone is 8-15 mm, wherein the upper end of the shoulder zone is connected to the cylindrical constant diameter zone in one body. The cylindrical constant diameter zone can be connected to a molecular pump. The quartz ampoule is sealed by hydrogen-oxygen flame after being vacuumized. The experimental cleaning steps are as follows: the instruments used for single crystal preparation are washed with ultrapure water, then immersed in a mixed solution of hydrochloric acid and sulfuric acid for 10-30 min, and finally the surface of the instruments is washed with ultrapure water and methanol to remove the mixed solution of hydrochloric acid and sulfuric acid. The cleaned experimental instruments are dried in a fume hood. The conditions for vacuumizing, heating and sealing are as follows: heating to 200-300℃, vacuum degree of 10 -5 -10-2 Pa, time is 2-3h, and the heating and vacuumizing are simultaneously carried out.

[0051] Example 1

[0052] The embodiment provides a preparation method of inch-level CsPbBr3 single crystal, and comprises the following steps:

[0053] 1) 630g of PbBr2 and CsBr powders are taken out, and are respectively placed in two crucibles to be heated to 180℃ and vacuumized (10 - 2 Pa) and dried for 3h; 600g of the dried PbBr2 and CsBr powders with a molar ratio of 1:1 are weighed by using a high-precision electronic balance; the PbBr2 and CsBr powders after the weighing are mixed in a mortar, and are sufficiently ground for 2h; after the white PbBr2 and CsBr mixed powders are ground into orange-yellow CsPbBr3 powders, the CsPbBr3 powders are loaded into an ampoule, vacuumized, heated and sealed; the ampoule is placed in a VGF furnace, and is heated to 600℃ within 6h and kept for 15h; finally, the ampoule is allowed to drop to room temperature within 40h; wherein the tip of the ampoule is provided with a 20° taper angle, and the length of the shoulder area is 12mm.

[0054] 2) the CsPbBr3 polycrystal obtained in step 1) is taken out, the surface impurities of the CsPbBr3 polycrystal are polished by using 800-mesh sandpaper, then the CsPbBr3 polycrystal is placed in an ultrasonic cleaning machine and cleaned for 1h, and finally the cleaned CsPbBr3 polycrystal is dried in an ultraclean interval fume hood; the CsPbBr3 polycrystal is loaded into an ampoule, vacuumized, heated and sealed; the ampoule is placed in a crystal growth cavity, 4 temperature measuring thermocouples are inserted into specific positions and fixed, and then a heat preservation cover is used to cover the top; the furnace body is heated to 560℃ within 6h and kept for 10h; the ampoule is allowed to drop to room temperature within 50h, the purified CsPbBr3 polycrystal is taken out, and the step is repeated for 3 times.

[0055] 3) the CsPbBr3 polycrystal after the impurities are removed is taken out, the surface impurities of the CsPbBr3 polycrystal are polished by using 1000-mesh sandpaper, then the CsPbBr3 polycrystal is placed in an ultrasonic cleaning machine and cleaned for 1h, and finally the crystal is placed in an ultraclean interval fume hood and volatilized with surface anhydrous ethanol, so as to be used as a precursor for single crystal growth;

[0056] 4) the precursor is loaded into a transparent quartz ampoule, vacuumized, heated, and the top of the ampoule is sealed by using a hydrogen-oxygen flame; the ampoule is placed in a crystal growth cavity, 4 temperature measuring thermocouples are inserted into specific positions and fixed, and then a heat preservation cover is used to cover the top;

[0057] 5) The segmented heating is divided into three stages: the first stage is 4h, four heating zones are simultaneously heated from room temperature to 300℃; the second stage is 3h, the first heating zone is heated to 320℃, the second heating zone is heated to 420℃, the third heating zone and the fourth heating zone are simultaneously heated to 500℃; the third stage is 1h, the first heating zone is heated to 480℃, the second heating zone is heated to 520℃, the third heating zone and the fourth heating zone are simultaneously heated to 610℃. After the target temperature is reached, the temperature is kept for 25h to make the precursor fully melt.

[0058] 6) The crystal growth cavity gradient cooling is divided into three stages: the first stage is 25h, the whole VGF furnace is simultaneously cooled from the third stage heating temperature to 180℃, wherein the cooling rate of the third and fourth heating zones is greater than that of the first and second heating zones, so as to reduce the temperature gradient in the VGF furnace; the second stage is 30h, and the temperature is simultaneously cooled to 65℃; the third stage is 6h, and the temperature is simultaneously cooled to room temperature.

[0059] The CsPbBr3 single crystal grown in Example 1 is shown in the schematic diagram as Figure 2 From the diagram, it can be seen that the obtained single crystal has high uniformity, high light transmittance, large size, no cracks and high flatness of the tail end. In order to determine the composition of the product, the sample prepared in Example 1 is subjected to X-ray diffraction test, as shown in Figure 3 The high-intensity diffraction peak indicates that the crystal grains have good crystallinity and consistent orientation; the absence of impurity peaks means that the obtained product is a high-quality CsPbBr3 single crystal. Figure 4 The transmittance spectrum of the CsPbBr3 single crystal obtained in Example 1 in the ultraviolet-visible-near infrared-mid infrared range is shown in the figure, and the transmittance in the range of 700-2000nm can reach more than 80%. The high transmittance indicates that the crystal has few defects and high quality.

[0060] Step 3) in the present application can effectively clean the impurities on the surface of the CsPbBr3 polycrystal, inhibit heterogeneous nucleation in the crystal growth, and further ensure that the single crystal has high uniformity and no cracks.

[0061] Example 2

[0062] The preparation method of this embodiment is the same as that of Example 1, and the only difference is that the first stage time in step 6) is 35h, the whole VGF furnace is simultaneously cooled from the third stage heating temperature to 150℃, wherein the cooling rate of the third and fourth heating zones is greater than that of the first and second heating zones, so as to reduce the temperature gradient in the VGF furnace; the second stage is 50h, and the temperature is simultaneously cooled to 60℃; the third stage is 4h, and the temperature is simultaneously cooled to room temperature.

[0063] The CsPbBr3 single crystal grown in Example 2 is shown in the schematic diagram as Figure 5As shown in the figure, compared with Example 1, the uniformity and transmittance of the single crystal obtained in Example 2 are similar to those of Example 1. Therefore, it can be proved that the cooling rate within the scope of the present patent can realize the preparation of high-quality inch-level CsPbBr3.

[0064] Example 3

[0065] The preparation method of this example is the same as that of Example 1, except that the step 5) of segmented heating is specifically as follows: the four heating zones are simultaneously raised from room temperature to 350℃ for 5h; the first heating zone is raised to 380℃, the second heating zone is raised to 490℃, the third heating zone is raised to 580℃ and the fourth heating zone is raised to 580℃ for 3h; the first heating zone is raised to 480℃, the second heating zone is raised to 550℃, the third heating zone is raised to 640℃ and the fourth heating zone is raised to 640℃ for 1h. After being raised to the target temperature, the crystal is kept for 25h to fully melt.

[0066] The schematic diagram of the CsPbBr3 single crystal grown in Example 3 is as shown in Figure 6 As shown in the figure, compared with Example 1 and Example 2, the uniformity and transmittance of the single crystal obtained in Example 3 are similar to those of Example 1.

[0067] Therefore, it can be proved that the heating process within the scope of the present patent can realize the preparation of high-quality inch-level CsPbBr3.

[0068] Comparative Example 1

[0069] The preparation method of Comparative Example 1 is the same as that of Example 1, except that the step 5) of segmented heating is specifically as follows: the four heating zones are simultaneously raised from room temperature to 300℃ for 5h; the first heating zone is raised to 320℃, the second heating zone is raised to 420℃, the third heating zone is raised to 500℃ and the fourth heating zone is raised to 500℃ for 3h; the first heating zone is raised to 480℃, the second heating zone is raised to 520℃, the third heating zone is raised to 680℃ and the fourth heating zone is raised to 680℃ for 1h. After being raised to the target temperature, the crystal is kept for 25h to fully melt.

[0070] The schematic diagram of the CsPbBr3 crystal grown in Comparative Example 1 is as shown in Figure 7 As shown in the figure, compared with Example 1, the uniformity of the crystal obtained in Comparative Example 1 is poor, the flatness at the tail end decreases, and there are a large number of CsPb2Br5 and Cs4PbBr6 on the surface of the crystal.

[0071] This is because, in the process of crystal growth, PbBr2 and CsBr also have other reactions, comparing the preparation methods of the two examples can be concluded that although setting the temperature value of the high temperature zone higher than the melting point of CsPbBr3 by 50-100 ℃ helps the crystal to fully melt, but the volatilization of components brought by over-temperature will cause the components in the crystal to deviate, the impurities increase, and then the heterogeneous nucleation appears in the process of crystal growth. Therefore, it can be proved that the temperature control process of the crystal is one of the important factors affecting the quality of the crystal.

[0072] Comparative Example 2

[0073] Comparative Example 2 has the same preparation method as Example 1, the only difference is that Comparative Example 2 cancels step 3) “polish the CsPbBr3 polycrystalline impurities with 1000 mesh sandpaper, then put them into an ultrasonic cleaning machine for ultrasonic cleaning for 1 h, and finally place the crystals in a clean bench fume hood to volatilize the surface anhydrous ethanol”.

[0074] The CsPbBr3 crystal grown in Comparative Example 2 is shown in the schematic diagram as Figure 8 From the figure, it can be seen that compared with Example 1, the crystal obtained in Comparative Example 2 has a relatively poor uniformity, the cracks increase obviously, the tail end color is deep, and there are more impurities.

[0075] The reason is that this process of ultrasonic cleaning of the precursor not only effectively removes the impurity powder remaining after polishing, but also removes the silicon carbide and other particles affecting the quality of the crystal remaining after polishing the crystal, and slows down the heterogeneous nucleation in the process of single crystal growth.

[0076] Therefore, it is proved that the treatment of CsPbBr3 polycrystalline impurities is one of the important factors affecting the quality of the crystal.

[0077] Comparative Example 3

[0078] Comparative Example 3 has the same preparation method as Example 1, the difference is that the step 5) is specifically: the first stage is to simultaneously raise the four heating zones from room temperature to 300 ℃ for 5 h; the second stage is to raise the first heating zone to 320 ℃, the second heating zone to 420 ℃, the third heating zone and the fourth heating zone to 500 ℃ for 3 h; the third stage is to raise the first heating zone to 480 ℃, the second heating zone to 520 ℃, the third heating zone and the fourth heating zone to 680 ℃ for 1 h. After rising to the target temperature, heat preservation for 25 h to make the crystal fully melt; at the same time, step 3) “polish the obtained CsPbBr3 polycrystalline impurities with 1000 mesh sandpaper, then put them into an ultrasonic cleaning machine for ultrasonic cleaning for 1 h, and finally place the crystals in a clean bench fume hood to volatilize the surface anhydrous ethanol” is cancelled.

[0079] The CsPbBr3 single crystal grown in Comparative Example 3 is shown in the schematic diagram as Figure 9As shown, compared with the crystal picture of Example 1, the crystal grown by Comparative Example 3 has a dark color, many internal impurities, poor uniformity, is obviously polycrystalline, and has many overall cracks.

[0080] It can be concluded that the impurity removal by ultrasonic cleaning and the precise temperature control process can reduce the heterogeneous nucleation phenomenon in the crystal growth process. This not only guarantees the uniformity of the crystal growth, but also improves the quality of the final single crystal. The optimization of these two process steps is an important link for realizing the growth of high-quality single crystals.

[0081] From the results of Examples 1, 2, 3 and Comparative Examples 1, 2, and 3, it can be concluded that the impurity removal of the polycrystalline precursor and the precise temperature control process are key factors for obtaining high-quality CsPbBr3 single crystals.

[0082] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for growing an inch-scale all-inorganic CsPbBr3 single crystal by VGF method, characterized in that, The method comprises the following steps: Step 1) taking CsPbBr3 polycrystal for impurity removal pretreatment to obtain polycrystal precursor; Step 2) loading the polycrystal precursor into a quartz ampoule, vacuumizing, heating and sealing, and then placing the ampoule in a crystal growth cavity, inserting 4-6 temperature measuring thermocouples at specific positions and fixing, and then covering the top with a heat preservation cover; Step 3) segmentally heating the crystal growth cavity and heat preserving to make the polycrystal precursor fully melt, and then gradiently cooling to room temperature after heat preservation ends, to obtain an inch-level all-inorganic CsPbBr3 single crystal; The crystal growth cavity in step 3) is a four-temperature-zone VGF furnace, which is sequentially a first heating zone, a second heating zone, a third heating zone and a fourth heating zone from bottom to top; The segmental heating in step 3) is divided into three stages: the first stage is 2-6 h, and the four heating zones are simultaneously heated from room temperature to 300-350 DEG C; the second stage is 1-3 h, and the first heating zone is heated to 300-400 DEG C, the second heating zone is heated to 400-500 DEG C, and the third heating zone and the fourth heating zone are simultaneously heated to 500-600 DEG C; the third stage is 1-3 h, and the first heating zone is heated to 450-550 DEG C, the second heating zone is heated to 500-600 DEG C, and the third heating zone and the fourth heating zone are simultaneously heated to 600-650 DEG C; the temperature of the VGF furnace is increased from bottom to top with a temperature gradient of 2-10 DEG C / cm; The heat preservation time in step 3) is 15-30 h; The gradient cooling in step 3) is divided into three stages: the first stage is 20-50 h, and the whole VGF furnace is cooled from the third stage heating temperature to 150-180 DEG C, wherein the cooling rate of the third and fourth heating zones is greater than that of the first and second heating zones, so as to reduce the temperature gradient in the VGF furnace; the second stage is 10-50 h, and each heating zone is simultaneously cooled to 60-70 DEG C; the third stage is 4-8 h, and each heating zone is simultaneously cooled to room temperature; In step 1), the CsPbBr3 polycrystal is prepared by using 2N purity PbBr2 and CsBr powder as raw materials; after the CsPbBr3 polycrystal is prepared, the CsPbBr3 polycrystal is impurity-removed for 2-4 times according to the impurity content; The dried PbBr2 and CsBr powder is weighed according to a molar ratio of 1:1, mixed in a mortar, and ground for 1-2 h; after the white PbBr2 and CsBr mixed powder is ground into orange-yellow CsPbBr3 powder, the powder is loaded into an ampoule, vacuumized, heated and sealed; the ampoule is placed in a VGF furnace, heated to 580-640 DEG C within 3-6 h and kept for 15-30 h; finally, the ampoule is cooled to room temperature within 40-70 h, and the CsPbBr3 polycrystal is taken out. The specific preparation steps of the CsPbBr3polycrystal are as follows: PbBr2and CsBr powders are respectively placed in two crucibles and heated to 180~260℃ while being vacuumized for 10 -5 ~10 -2 Pa, and dried for 1~3h. ​ The impurity removal of the CsPbBr3 polycrystal comprises the following steps: removing impurities from the surface and tail end of the CsPbBr3 polycrystal; loading the treated CsPbBr3 polycrystal into an ampoule, vacuumizing, heating, and sealing the ampoule; loading the ampoule into a crystal growth cavity, inserting 4-6 temperature measuring thermocouples at specific positions and fixing the thermocouples, covering the top of the ampoule with a heat preservation cover; heating the furnace body to 560-620 DEG C within 6-10 h and keeping the temperature for 10-20 h; and cooling the ampoule to room temperature within 40-100 h and taking out the purified CsPbBr3 polycrystal. The two ends and the impurities with darker color on the surface of the CsPbBr3 polycrystal are polished with 500-3000 mesh sandpaper, then the polycrystal is placed in anhydrous ethanol and ultrasonic cleaned in an ultrasonic cleaning machine for 1-2 h, and finally the crystal is placed in a clean bench fume hood and the anhydrous ethanol on the surface is volatilized.

2. The method of claim 1, wherein, The inner diameter of the quartz ampoule in the step 2) is 25-65 mm, the wall thickness is 2-4 mm, the sharp end of the ampoule is provided with a 15-25 DEG C cone angle, and the length of the shoulder area is 8-15 mm.

3. The method of claim 1, wherein, The heating temperature in the step 2) is 160-300℃, the time is 2-3h; the vacuum degree of vacuumizing is 10 -5 ~10 -2 Pa; the time is 1-8h; the sealing mode is sealed by hydrogen oxygen flame; the heating and vacuumizing are simultaneously carried out.

4. The method of claim 1, wherein, Before each step, the experimental apparatus needs to be cleaned, and the specific steps are as follows: first, the apparatus is washed with ultrapure water to remove large impurities, then the washed apparatus is immersed in a mixed solution of hydrochloric acid and sulfuric acid for 10-30 min, and finally the apparatus is washed with ultrapure water and methanol in sequence to remove the residual mixed solution of hydrochloric acid and sulfuric acid.

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