Prenucleation-assisted spatial confinement method for high-quality perovskite thin single crystal growth

Abstract

The invention discloses a pre-nucleation-assisted spatial confinement method for high-quality perovskite thin single crystal growth, which comprises the following steps: preparing an organic-inorganic hybrid perovskite precursor solution, dissolving the organic-inorganic hybrid perovskite precursor solution in a DMF (Dimethyl Formamide) solvent, stirring, and standing at room temperature to obtain a nearly saturated solution; the asymmetric substrates are combined to form a micron-sized two-dimensional confinement space by using a strong clamp; adding the nearly saturated solution into a two-dimensional confinement space for fixation, and then carrying out heat treatment to obtain a pre-nucleated perovskite thin single crystal; and growing the pre-nucleated perovskite thin single crystal at constant temperature and constant humidity to obtain the high-quality perovskite thin single crystal, the constant temperature ranges from 23 DEG C to 27 DEG C, and the constant humidity ranges from 35% to 45%. A device prepared from the crystal grown by the method shows higher device performance and working stability.

Description

Technical Field

[0001] The invention belongs to the field of perovskite photoelectric devices, and in particular relates to a pre-nucleation-assisted spatial confinement method for growing high-quality perovskite thin single crystals. Background Art

[0002] In recent years, lead halide perovskites have become potential materials for building optoelectronic devices due to their excellent optoelectronic properties. However, the active layers in current perovskite optoelectronic devices are mostly perovskite polycrystalline thin film materials, in which a large number of grain boundaries and defects will hinder the transport of carriers, resulting in serious hysteresis and performance degradation in the device, which seriously hinders the practical application and commercialization of perovskites. Especially in the field of light-emitting diodes, defects in perovskite polycrystalline thin films seriously limit the development of devices. The grain-boundary-free perovskite single crystal system has fewer defects, exhibits highly ordered lattice stacking, outstanding optoelectronic properties and excellent stability, and is expected to replace perovskite polycrystalline thin films as active layer materials for optoelectronic devices. At present, mature single crystal growth methods are mostly focused on the growth of bulk single crystals, but the large thickness (>1mm) of bulk single crystals limits their application in optoelectronic devices. In order to meet the actual device applications, the preparation of high-quality, thin (micrometer level) perovskite single crystals has become the key to the development of single crystal optoelectronic devices.

[0003] The method currently widely used for the growth of thin single crystals is the spatial confinement method, that is, by physically confining the precursor liquid between the substrates, and changing the pressure applied to the substrate to change the distance between the two substrates, the thickness of the crystal growth can be controlled. However, the precursor liquid in this method is confined between the two substrates, and it is impossible to perform effective crystal nucleation and efficient single crystal growth through the volatilization of its own solvent. The currently reported method is to combine this method with the inversion crystallization method, by placing it at a high temperature (80-130°C) for growth. Because the solubility of perovskite in a specific solvent decreases with increasing temperature, at high temperatures, the solubility drops below the solution concentration, the precursor liquid reaches supersaturation, and the crystals still precipitate and grow. Although this spatial confinement method for crystal preparation at high temperature can obtain thinner (<2μm) perovskite single crystals, the grown perovskite single crystals still cannot meet the requirements of practical applications due to the following shortcomings: 1) The heating process and high-temperature growth environment will cause thermal disturbances, affecting the transmission of solutes in the precursor solution and the deposition on the precipitated crystals, thereby reducing the long-range order of the lattice stacking and introducing a large number of structural defects inside the crystal, which will further cause the degradation of device performance; 2) The organic components in the perovskite are easily decomposed during the long-term high-temperature growth process, which will further degrade the optical properties of the crystal, resulting in poor and uneven fluorescence emission; 3) In this method, crystal nucleation and growth are carried out simultaneously during the heating process, which will cause the crystal to continuously form new grains during the growth process. This random continuous nucleation leads to the formation of a large number of microcrystals and twins, which poses a huge challenge to the subsequent device construction. Therefore, it is still a huge challenge to grow high-quality, low-defect perovskite thin single crystals to meet the actual application of optoelectronic devices. Summary of the invention

[0004] The purpose of this section is to summarize some aspects of embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the specification abstract and the invention title of this application to avoid blurring the purpose of this section, the specification abstract and the invention title, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0005] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0006] An object of the present invention is to overcome the deficiencies in the prior art and provide a pre-nucleation-assisted spatial confinement method for the growth of high-quality perovskite thin single crystals.

[0007] As a preferred embodiment of the preparation method of the present invention, an organic-inorganic hybrid perovskite precursor solution is prepared, the organic-inorganic hybrid perovskite precursor solution is dissolved in a DMF solvent and stirred, and a nearly saturated solution is obtained after standing at room temperature;

[0008] Asymmetric substrates are combined using strong clamps to form a two-dimensional confined space at the micrometer level;

[0009] After adding a nearly saturated solution into a two-dimensional confined space and fixing it, a heat treatment is performed to obtain a pre-nucleated perovskite thin single crystal;

[0010] Growing the pre-nucleated perovskite thin single crystal under constant temperature and humidity to obtain the high-quality perovskite thin single crystal;

[0011] The constant temperature is 23° C. to 27° C., and the constant humidity is 35% to 45%.

[0012] As a preferred embodiment of the preparation method of the present invention, the asymmetric substrate combination is a strongly hydrophobic growth substrate and a weakly hydrophobic growth substrate.

[0013] As a preferred embodiment of the preparation method of the present invention, the preparation method of the asymmetric substrate combination of a strongly hydrophobic growth substrate and a weakly hydrophobic growth substrate is as follows: the substrate is ultrasonically cleaned with a detergent, ultrapure water, acetone and ethanol in sequence, blown dry with nitrogen, and preheated after hydrophilic treatment in an ultraviolet ozone machine, and then FTS reagent is added, vacuumed and modified, and the vacuum is broken and then cooled to room temperature to obtain a strongly hydrophobic growth substrate;

[0014] The substrate preheated in the above step is added with a 1000-fold diluted FTS solution and vacuum-modified, and then the vacuum is broken and cooled to room temperature to obtain a weakly hydrophobic growth substrate.

[0015] As a preferred embodiment of the preparation method of the present invention, the molar ratio of the organic component to the inorganic component in the organic-inorganic hybrid perovskite precursor solution is 1.05 to 2:1.

[0016] As a preferred solution of the preparation method of the present invention, the substrate includes ITO, glass substrate, FTO, SiO2, and a transmission layer with PTAA, Poly-TPD, PMMA, and SnO2, and the size is 2cm×2cm.

[0017] As a preferred embodiment of the preparation method of the present invention, the heat treatment temperature is 60°C to 80°C, and the time is 30s to 10min.

[0018] As a preferred embodiment of the preparation method of the present invention, the amount of the FTS reagent added is 4 to 5 μL.

[0019] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a perovskite thin single crystal.

[0020] In order to solve the above technical problems, the present invention provides the following technical solution: the perovskite thin single crystal has a regular quadrilateral morphology and crystal structure.

[0021] As a preferred embodiment of the preparation method of the present invention, the perovskite thin single crystal is a three-dimensional organic-inorganic hybrid perovskite.

[0022] As a preferred embodiment of the preparation method of the present invention, wherein:

[0023] (i) Perovskite thin single crystals have ~10 3 aspect ratio;

[0024] (ii) The lateral size of perovskite thin single crystals can reach millimeter level, and the crystal thickness is less than 2μm;

[0025] (iii) The perovskite thin single crystal has high crystalline quality and low defect state density, where the rocking curve of the diffraction peak is 0.021°±0.0041° and the defect state density is 1.77×10 10 cm -3 ~3.57×10 10 cm -3 ;

[0026] (iv) The perovskite thin single crystals have excellent optical properties, with a PLQY of 30.2±2.5% and uniform fluorescence emission characteristics at different locations of a single crystal;

[0027] (v) The light-emitting diode device prepared from the perovskite thin single crystal has excellent device performance, wherein the brightness can reach 202,600 cd m-2, the EQE can reach 5.6%, and the -2 and 10890cd m -2 The half-life times at initial brightness can reach 183.2min and 24.2min respectively.

[0028] Beneficial effects of the present invention:

[0029] The pre-nucleation-assisted spatial confinement method developed in the present invention purposefully separates the crystal nucleation process from the crystal growth process, and realizes the preparation of high-quality perovskite single crystals at room temperature. The method also has the following advantages: the growth temperature is reduced, the growth process is more stable, there are fewer defects in the crystal, and the crystal quality is higher; the decomposition of organic components at high temperatures is avoided, and the optical properties of the prepared crystals are more uniform; the crystal nucleation is controlled through the pre-nucleation process, the number of nucleations is effectively reduced, and the growth of large-sized, regular-shaped crystals is promoted; the devices prepared by the crystals grown by this method show higher device performance and working stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0031] Figure 1 This is a graph showing the variation of Gibbs free energy with grain size in Example 1 of the present invention.

[0032] Figure 2 The dissolution curve and fluorescence photograph of Example 1 of the present invention, wherein: Figure 2 (a) Solubility curve of MAPbBr3 in DMF; Figure 2 (b) Fluorescence photograph of pre-nucleated seeds under UV light.

[0033] Figure 3 1 is a comparison between the traditional spatial confinement method and the pre-nucleation assisted spatial confinement method in Example 4 of the present invention.

[0034] Figure 4 is an optical photograph of Example 4 of the present invention, wherein: Figure 4 (a) Optical photograph of MAPbBr3 single crystal grown at high temperature; Figure 4 (b) Direct growth at room temperature and Figure 4 (c) Optical photograph of MAPbBr3 single crystal grown at room temperature after pre-nucleation treatment (scale bar is 5 mm).

[0035] Figure 5 The comparison of the crystal quality of MAPbBr3 single crystals grown by two methods in the embodiment of the present invention is shown in FIG. Figure 5 (a) Comparison of defect state density; Figure 5 (b) Comparison of the XRD rocking curves of the (001) and (002) diffraction peaks.

[0036] Figure 6 The optical properties of MAPbBr3 single crystals grown by two methods in the embodiments of the present invention are compared, wherein: Figure 6 (a) Comparison of PLQY of the two crystals; Figure 6 (b) Comparison of carrier lifetimes of the two crystals.

[0037] Figure 7 The fluorescence uniformity of MAPbBr3 single crystals grown by two methods in the present invention is compared, wherein: Figure 7 (a) Comparison of fluorescence microscopy images of the two crystals; Figure 7 PL mapping of (b) Pre-MAPbBr3 single crystal and (c) Tra-MAPbBr3 single crystal.

[0038] Figure 8 The structure diagram and cross-sectional SEM of an LED based on a perovskite single crystal according to an embodiment of the present invention are shown in FIG. Figure 8 (a) Schematic diagram of the device structure. Figure 8 (b) is the corresponding cross-sectional SEM.

[0039] Fig. 9 The LED performance of MAPbBr3 single crystals grown by two methods in the present invention is compared, wherein: Fig. 9 (a) is brightness, Fig. 9 (b) is the comparison of current efficiency.

[0040] Fig.10 The universality of the pre-nucleation assisted spatial confinement method of the embodiment of the present invention, wherein, Fig.10 (a) is an optical micrograph and a fluorescence micrograph of a FAPbBr3 single crystal. Fig.10 (b) is the XRD spectrum; Fig.10 (c) is an optical micrograph and a fluorescence micrograph of a CsPbBr3 single crystal. Fig.10 (d) is the XRD spectrum. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0042] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0044] According to the classical nucleation theory, the growth of a single crystal is divided into two continuous processes: nucleation and growth. Nucleation is the prerequisite for growth and the key to the entire crystallization process. The process of crystal precipitation from solution can be described by the change in Gibbs free energy (ΔG), where ΔG has a maximum value, corresponding to the nucleation barrier ΔG* for crystal growth, and the nucleus size corresponding to the maximum value is the critical size r*( Figure 1). When the precipitated grains do not reach the critical size, the grains will dissolve back into the precursor solution. Only the grains that reach the critical size can be used as seeds to further grow into perovskite single crystals. Therefore, the key to achieving the spontaneous growth of perovskite single crystals at room temperature is to obtain grains larger than the critical size as seeds for the next step of growth.

[0045] The raw materials used in the examples of the present invention are commercially available unless otherwise specified, as shown in Table 1.

[0046] Table 1

[0047]

[0048]

[0049] Example 1

[0050] (1) Preparation of perovskite precursor solution: We weighed 587.2 mg of lead bromide and 188.16 mg of methylamine bromide powder, dissolved them in 1 mL of DMF solvent, stirred them with a magnetic stirrer for three hours, and then left them at room temperature overnight to prepare a concentration of 1.6 mmol mL -1 A nearly saturated solution.

[0051] (2) Preparation of asymmetric hydrophobic substrate: The cut ITO or glass substrate (2cm×2cm) was ultrasonically cleaned with detergent, ultrapure water, acetone and ethanol in turn. The cleaned growth substrate was blown dry with nitrogen and placed in a glass culture dish, and hydrophilic treatment was performed in a UV ozone machine for 15 minutes. The hydrophilic growth substrate was then transferred to a 90°C oven for preheating for 15 minutes. Next, 4-5μL of the original FTS solution was quickly dripped into the glass culture dish, and the vacuum degree of the oven was evacuated to 50mbar. The substrate was modified under low pressure and 90°C for 10 minutes. After breaking the vacuum, it was taken out and cooled to room temperature to prepare a strongly hydrophobic growth substrate. In addition, while ensuring that the above conditions remain unchanged, the growth substrate was modified with FTS diluted 1000 times with n-butanol to prepare a weakly hydrophobic growth substrate.

[0052] (3) Pre-nucleation-assisted spatial confinement method to grow MAPbBr3 single crystals: Take the prepared perovskite solution (~2μL) and drop it on a weakly hydrophobic growth substrate, then gently cover it with another strongly hydrophobic growth substrate and fix it with a binder clip. Then put it in an oven at 60℃ for rapid heat treatment for 5min. According to the solubility curve of MAPbBr3 in DMF ( Figure 2 a), the solubility at 60℃ is 34% lower than the solution concentration. At this time, the solution is supersaturated and crystals begin to precipitate on the substrate. We use a UV flashlight to observe the precipitation of crystals in real time. When small crystals precipitate in the substrate ( Figure 2b), the sample is taken out of the oven and placed at room temperature for growth (~25°C). After ~15 days of growth, a millimeter-scale MAPbBr3 single crystal with a regular shape can be obtained.

[0053] The present invention attempts screening experiments on different concentrations and pre-nucleation treatment times in the preparation of perovskite precursor solution, as shown in Table 2 below. We have optimized the growth environment: the growth is carried out in a constant humidity room with a seed temperature of 25°C ± 2°C and a humidity of 40% ± 5%.

[0054] Table 2

[0055] 80℃ 60℃ <![CDATA[1.8mmolmL -1 ]]> ～30s ~1min <![CDATA[1.6mmolmL -1 ]]> ~1min ~5min <![CDATA[1.4mmolmL -1 ]]> ~10min ~30min

[0056] Example 2

[0057] The difference from Example 1 is that in step (1), 513.8 mg of lead bromide and 183.7 mg of formamidine bromide powder were weighed and dissolved in 1 mL of a mixed solvent of DMF / GBL, wherein the volume ratio of DMF to GBL was 1:1. The mixture was stirred by a magnetic stirrer for three hours and then allowed to stand at room temperature overnight to prepare a concentration of 1.4 mmol mL -1 A nearly saturated solution.

[0058] The difference from Example 1 is that in step (3), FAPbBr3 precursor solution is used for crystal growth, and finally FAPbBr3 single crystal is obtained.

[0059] Example 3

[0060] The difference from Example 1 is that in step (1), 146.8 mg of lead bromide and 170.25 mg of cesium bromide powder were weighed and dissolved in 1 mL of DMSO solvent. The mixture was stirred for three hours by a magnetic stirrer and then allowed to stand at room temperature overnight to prepare a concentration of 0.4 mmol mL -1 A nearly saturated solution.

[0061] The difference from Example 1 is that in step (3), a CsPbBr3 precursor solution is used for crystal growth, and finally a CsPbBr3 single crystal is obtained.

[0062] Comparative Example 1

[0063] This comparative example provides a MAPbBr3 single crystal grown by a traditional spatial confinement method and is labeled as Tra-MAPbBr3 single crystal.

[0064] The difference from Example 1 is that in step (3), we take the prepared perovskite solution (~2 μL) and drop it on the weakly hydrophobic growth substrate, then gently cover it with another strongly hydrophobic growth substrate and fix it with a binder clip. Then put it in an oven for inversion crystal growth at 5°C h -1 The heating rate is increased from room temperature to 80°C, and then the Tra-MAPbBr3 single crystal is obtained by constant growth at 80°C for 12 hours.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that in step (1), according to the literature (Crystallization of CsPbBr3 Single Crystals in Water for X-Ray Detection. Nat. Commun. 2021, 12 (1), 1531.), CsBr and PbBr2 powders with a molar ratio of 1:1 were dissolved in HBr to prepare a precursor solution of CsPbBr3. According to the literature (Preferential Facet Growth of Methylammonium Lead Halide Single Crystals Promoted by Halide Coordination. Chemistry Letters 2016, 45 (8), 1030-1032), MABr and PbBr2 powders with a molar ratio of 1:1 were dissolved in HBr to prepare a precursor solution of MAPbBr3.

[0067] The solubility of MAPbBr3 in 40% aq.HBr and CsPbBr3 in 48% aq.HBr decreases with increasing temperature. Pre-nucleation cannot obtain effective seeds and the corresponding perovskite single crystals cannot be grown at room temperature.

[0068] Example 4

[0069] Figure 3 A comparison is given between the conventional spatial confinement method of comparative example 1 and the pre-nucleation-assisted spatial confinement method of the present invention. Figure 3As shown in the upper part of the figure, in order to induce crystal nucleation and promote crystal growth, the growth of perovskite single crystals in the traditional spatial confinement method is usually carried out at a higher temperature (80℃-130℃). Since the solubility of perovskite in a specific solvent decreases with the increase of temperature, the precursor solution will eventually reach supersaturation due to the solubility being lower than the concentration. When the supersaturation of the precursor solution increases to a certain extent, the nucleation energy barrier of the perovskite crystal is overcome, thereby triggering the nucleation process of the crystal. At the same time, the high-temperature growth environment can promote the transport of solutes and increase the growth rate of perovskite single crystals. Although the traditional spatial confinement method solves the crystal nucleation problem and realizes the rapid growth of lead halide perovskite single crystals, the crystals prepared by this method show poor crystal quality and low PLQY due to a large number of defects in the body. The heating process and high-temperature growth environment in the traditional spatial confinement method will cause disorder in the solute transport and deposition during the crystal growth process, thereby destroying the orderly stacking of the crystal lattice and generating a large number of crystal defects in the crystal. In addition, the organic components in perovskite are easily decomposed during long-term high-temperature growth, which will further degrade the optical properties of the crystal, resulting in poor and uneven fluorescence emission. In addition, crystal nucleation and growth occur simultaneously during the heating process, which will lead to the continuous formation of new grains during the growth process. Figure 4 As shown in a, this random continuous nucleation leads to the formation of a large number of crystallites and twins, posing a huge challenge to the subsequent device construction.

[0070] Lowering the growth temperature is an effective way to improve crystal quality and device performance. However, in the spatial confinement method, the precursor solution is confined to a narrow gap between the two substrates (about a few microns), and the solvent evaporates very slowly, which means that the solution cannot cause effective crystal nucleation by its own solvent evaporation alone, and thus the growth of the target perovskite single crystal cannot be achieved at room temperature. Figure 4 As shown in b, due to the lack of effective nucleation, the precursor solution between the two substrates cannot obtain ideal crystals even if it grows for several weeks.

[0071] To overcome the problems discussed above, we developed a pre-nucleation-assisted spatial confinement method for growing lead halide perovskite single crystals at room temperature. Figure 3 As shown in the lower part of , we first obtain pre-nucleated small seeds by a rapid heat treatment ( Figure 2) and then place it directly in a constant laboratory for growth. Among them, when the size of the pre-nucleated grains is larger than r*, these grains will act as seeds and further spontaneously grow into single crystals at room temperature, while the grains that have not reached r* will dissolve back into the precursor solution. It is worth noting that due to the constant room temperature growth environment, the transport and deposition of the solute are more stable, and the defects in the crystal are significantly reduced, so the grown perovskite single crystals also have higher crystal quality and better optical properties. In addition, this method intentionally separates the crystal nucleation process from the growth process (the nucleation process is completed in the pre-nucleation stage, and only the crystal growth process exists at room temperature), thereby effectively reducing the number of nucleations. The reduction of nucleation points is conducive to the growth of larger and better morphological perovskite single crystals ( Figure 4 c) Single crystals grown by this method show great potential in the preparation of high-performance optoelectronic devices.

[0072] Example 5

[0073] Crystal quality characterization of MAPbBr3 single crystals:

[0074] In order to highlight the advantages of the pre-nucleation assisted spatial confinement method in preparing high-quality perovskite single crystals, we compared it with the perovskite single crystals grown by the traditional spatial confinement method. For the convenience of expression, the MAPbBr3 single crystals grown by the pre-nucleation assisted spatial confinement method are marked as Pre-MAPbBr3 single crystals, and the MAPbBr3 single crystals grown by the traditional spatial confinement method are marked as Tra-MAPbBr3 single crystals.

[0075] Comparison of crystal quality: The most significant change in Pre-MAPbBr3 single crystal compared to Tra-MAPbBr3 single crystal is the decrease in defect state density. Figure 5 a shows the statistical diagram of the defect state density of the two crystals. The average defect state density of Pre-MAPbBr3 single crystal is (2.67±0.9)×10 10 cm 3 , compared with Tra-MAPbBr3 single crystal ((1.25±0.6)×10 11 cm 3 ) is almost one order of magnitude lower. The half-peak width of the XRD rocking curve is another method to characterize the quality of crystallinity. Figure 5 b shows the comparison of the half-peak width of the rocking curves of the two crystals at (001) and (002), where the half-peak widths of the rocking curves of the Pre-MAPbBr3 single crystal at the two diffraction peaks are 0.021±0.0041 and 0.019±0.0042, respectively, which are significantly lower than those of the Tra-MAPbBr3 single crystal (0.051±0.011 and 0.052±0.016). The above results show that the pre-nucleation strategy effectively improves the crystallization quality of perovskite single crystals.

[0076] Comparison of optical properties: Perovskite single crystals with good optical properties are an important prerequisite for achieving excellent device performance. We then compared the optical properties of the two single crystals. Figure 6 a shows the comparison of the PLQY of the two crystals, where the average PLQY of the Pre-MAPbBr3 single crystal is 30.24±2.46%, which is nearly 5 times higher than that of the Pre-MAPbBr3 single crystal (5.69±1.47%). It can also be clearly seen from the fluorescence photos of the two crystals under UV light that the fluorescence of the Pre-MAPbBr3 single crystal is more intense, indicating stronger PL characteristics. We fitted the TRPL spectra of the two crystals to obtain two carrier lifetimes, of which the smaller value of τ surface Corresponding to the recombination of carriers on the crystal surface, the larger value of τ bulk corresponds to the recombination of carriers in the crystal. Figure 6 As shown in b, Pre-MAPbBr3 single crystal has no surface Or τ bulk The values ​​of Pre-MAPbBr3 single crystals are significantly larger than those of Tra-MAPbBr3 single crystals, indicating that Pre-MAPbBr3 single crystals have higher optical properties. Figure 7 a) and micro-area PLmapping ( Figure 7 b, c) It can be clearly seen that the MAPbBr3 single crystal grown at room temperature has more uniform fluorescence properties.

[0077] Example 6

[0078] Comparison of device performance (taking LED devices as an example):

[0079] The present invention prepares the perovskite crystal prepared by the above method into an LED device, and compares the device performance.

[0080] First, the grown MAPbBr3 single crystals were selected, and crystals with regular shape, smooth surface and large size were selected for device construction. Then, PMMA solution (concentration of 0.13 g mL in chlorobenzene) was scraped with a scraper. -1 ) to one side of the crystal. Note that PMMA does not completely cover the crystal, but only covers the edge of the crystal. Repeat the above steps until the ITO at the edge of the crystal is completely covered by PMMA. After PMMA solidifies, transfer it to an organic-metal thermal evaporation coating instrument and coat it under low vacuum (<1×10 4 Pa) and then evaporated TPBi (30nm, )、LiF(1nm, ) and Al(120nm, ), to construct a single crystal PeLED. Among them, the PMMA layer plays the role of an insulating layer on the one hand, avoiding direct contact between the upper and lower electrodes of the device and short circuit; on the other hand, it plays the role of a lead electrode. The surface of the solidified PMMA is smooth, and the electrode on the surface of the crystal can be led to the outside, which is convenient for subsequent device testing. Figure 8 The schematic diagram of the device structure and the corresponding cross-sectional SEM, where MAPbBr3 single crystals are grown directly on the ITO substrate, and then 40nm TPBi, 1nm LiF and 120nm Al are sequentially evaporated on the crystal surface. The average device brightness and current efficiency of the Pre-MAPbBr3 single crystal LED are 104 and 304 cd m -2 and 17.9cd A -1 , which are significantly higher than those based on Tra-MAPbBr3 single crystal LED (20,894 cd m -2 and 3.98cd A -1 )( Fig. 9 ).

[0081] The pre-nucleation-assisted spatial confinement method developed by the present invention not only effectively improves the crystal quality and optical properties of the crystal, but also significantly improves the device performance of the corresponding LED. In addition, the pre-nucleation-assisted spatial confinement method developed by the present invention can also be used to grow other types of perovskite single crystals, such as FAPbBr3 single crystals and CsPbBr3 single crystals (Examples 2 and 3), such as Fig.10 shown.

[0082] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims

1. A pre-nucleation-assisted spatial confinement method for the growth of high-quality perovskite thin single crystals, characterized in that: include: An organic-inorganic hybrid perovskite precursor solution is prepared, the organic-inorganic hybrid perovskite precursor solution is dissolved in a DMF solvent and stirred, and a nearly saturated solution is obtained after standing at room temperature; Asymmetric substrates are combined using strong clamps to form a two-dimensional confined space at the micrometer level; After adding a nearly saturated solution into a two-dimensional confined space and fixing it, a heat treatment is performed to obtain a pre-nucleated perovskite thin single crystal; The high-quality perovskite thin single crystal is grown by pre-nucleating the thin single crystal at a constant temperature and humidity to obtain the thin single crystal; the constant temperature is 23° C. to 27° C., and the constant humidity is 35% to 45%.

2. The spatial confinement method according to claim 1, characterized in that: The asymmetric substrate combination is a strongly hydrophobic growth substrate and a weakly hydrophobic growth substrate.

3. The spatial confinement method according to claim 2, characterized in that: The preparation method of the asymmetric substrate combination as a strongly hydrophobic growth substrate and a weakly hydrophobic growth substrate is as follows: the substrate is ultrasonically cleaned with a detergent, ultrapure water, acetone and ethanol in sequence, blown dry with nitrogen, and preheated after hydrophilic treatment in an ultraviolet ozone machine, and then FTS reagent is added, vacuumed and modified, and the vacuum is broken and then cooled to room temperature to obtain a strongly hydrophobic growth substrate; the substrate preheated in the above step is added with a 1000-fold diluted FTS solution, vacuumed and modified, and the vacuum is broken and then cooled to room temperature to obtain a weakly hydrophobic growth substrate.

4. The spatial confinement method according to claim 1, characterized in that: The molar ratio of the organic component to the inorganic component in the organic-inorganic hybrid perovskite precursor solution is 1.05 to 2:

1.

5. The spatial confinement method according to claim 2, characterized in that: The substrate comprises ITO, a glass substrate, FTO, SiO2, a transmission layer with PTAA, Poly-TPD, PMMA, and SnO2 spun on it, and has a size of 2cm×2cm.

6. The spatial confinement method according to claim 1, characterized in that: The heat treatment temperature is 60° C. to 80° C., and the time is 30 s to 10 min. The amount of FTS reagent added is 4 to 5 μL.

7. A high-quality perovskite thin single crystal obtained by the spatial confinement method according to any one of claims 1 to 6.

8. The perovskite thin single crystal according to claim 7, characterized in that: The perovskite thin single crystal has the following characteristics: (i) Perovskite thin single crystals have ~10 3 aspect ratio; (ii) The lateral size of perovskite thin single crystals can reach millimeter level, and the crystal thickness is less than 2μm; (iii) The perovskite thin single crystal has high crystalline quality and low defect state density, where the rocking curve of the diffraction peak is 0.021°±0.0041° and the defect state density is 1.77×10 10 cm -3 ~3.57×10 10 cm -3 ; (iv) The perovskite thin single crystals have excellent optical properties, with a PLQY of 30.2±2.5% and uniform fluorescence emission characteristics at different locations of a single crystal; (v) The light-emitting diode device prepared from the perovskite thin single crystal has excellent device performance, with a brightness of up to 202,600 cd m -2 , EQE can reach 5.6% at 1024cd m -2 and 10890cd m -2 The half-life times at initial brightness can reach 183.2min and 24.2min respectively.

9. The perovskite thin single crystal according to claim 8, characterized in that: The perovskite thin single crystal has a regular tetragonal morphology and crystal structure.

10. The perovskite thin single crystal according to claim 9, characterized in that: The perovskite thin single crystal is a three-dimensional organic-inorganic hybrid perovskite.

Images