A method for morphology-controllable preparation of all-inorganic CsPbBr3 perovskite nanorods

Abstract

The application discloses a method for preparing full-inorganic CsPbBr3 perovskite nanorods with controllable morphology, which comprises the following steps: by controlling the amount of water added and the ligand, high-luminous perovskite quantum dots from nanocrystals to nanorods in size can be controllably prepared; the CsPbBr3 nanorods are directly synthesized in a non-polar solution, the process of further purification is omitted, and the CsPbBr3 nanorods can be directly stored after the reaction; because the precursor PbBr2 ligand solution not only participates in the synthesis reaction but also constantly passivates the generated CsPbBr3 nanorods during the reaction, the anti-humidity stability of the prepared CsPbX3 nanomaterial is significantly enhanced, the luminous wavelength is in the range of 514-522 nm, and the anisotropy value reaches 0.15. The application not only provides a new way for preparing high-luminous CsPbX3 quantum dots, but also provides a new possibility for the industrialization and mass production of perovskite quantum dots in the future because the precursor can be well stored for a long time and the reaction process is simple and effective.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor material preparation technology, specifically relating to a method for preparing all-inorganic CsPbBr3 perovskite nanorods with controllable morphology. Background Technology

[0002] Since the beginning of the new century, with the advancement of science and technology, the continuous consumption of energy has led to increasingly prominent problems such as energy crises and environmental pollution, which have begun to affect all aspects of human life. In recent years, considering the efficient use of energy and in order to reduce the costs of modern civilization development, researchers have been continuously researching and developing various green materials from the perspective of materials themselves. In the field of display, polarization optical devices have always been an important research direction. For example, the plastic polarizers in liquid crystal displays today have an energy loss rate as high as 50% (45%). Therefore, if a light-emitting material with its own polarization effect can be developed, it can replace the plastic polarizers in traditional display panels, greatly reducing energy loss. Some semiconductor materials themselves have anisotropic crystal structures or morphologies, belonging to the category of polarization-sensitive materials, and can directly emit and detect polarized light. More importantly, using polarization-sensitive materials can avoid the use of bulky and rigid optical components, which makes them show unprecedented application prospects in large-scale integration and flexible electronics. In the early stages, inorganic compound semiconductors were used as polarization-sensitive materials for linearly polarized luminescence and detection, such as one-dimensional InP, ZnO, and CdSe nanowires, and two-dimensional black phosphorus, silicene, and germanene nanosheets. Currently, the types and performance of luminescent materials with polarization properties remain relatively limited; therefore, the search for highly efficient polarized luminescent materials remains a key research focus in this field.

[0003] Lead halide perovskites (APbX3) (A = Cs, MA, FA, X = Cl, Br, I) have attracted widespread attention due to their excellent optoelectronic properties, such as highly saturated emission, easily tunable emission wavelength within the visible spectrum, and high photoluminescence quantum yield (PLQY). Since the pioneering work of Kovalenko's group in 2015, the preparation and application of CsPbX3 quantum dots have made considerable progress in a short period of time. For example, CsPbX3 nanomaterials with controllable shape and composition have been prepared using hot-injection, solvothermal, ultrasonic, room-temperature precipitation, chemical vapor deposition, and interface conversion methods. The prepared CsPbX3 quantum dots have been used in many potential applications, including solar cells, lasers, light-emitting diodes, and photodetectors. Among them, one-dimensional APbX3 nanorods, with strong bound excitons (>100 meV binding energy), larger transition energies, and sharp emission peaks, are considered ideal components for future integrated optoelectronic devices.

[0004] Although many methods have been developed to obtain perovskite nanorods, there are still few methods for the controlled direct synthesis of perovskite nanorods with different sizes. This is because the nucleation and growth rates of perovskite nanocrystals are very fast, making it more difficult to achieve nanorods with controllable shapes and sizes. To obtain perovskite nanorods with tunable emission wavelengths, Tong et al. reported an experiment in which ligand-induced CsPbBr3 perovskite nanowires fractured into low aspect ratio CsPbX3 (X = Cl, Br, and I) nanorods in a solution exchange reaction with halide PbX2 ligands. The shape transformation from nanowires to nanorods led to a decrease in nonradiative attenuation rate, thereby improving photoluminescence efficiency (Angew. Chem. Int. Ed. 2018, 57, 16094–16098). To obtain perovskite nanorods with controllable shape synthesis, Zhang's group treated pre-prepared non-luminescent Cs4PbX6 nanocrystals with water at the water / oil interface. By controlling the concentration of Cs4PbX6 and the reaction time, they were able to obtain CsPbX3 nanorods with controllable aspect ratios, which is of great significance for interfacial synthesis of nanorods (Chem. Mater. 2019, 31, 1575). Huang's group used a vortex method at the water-hexane interface to synthesize Pb... 2+ CsPbBr3 nanorods were prepared by inserting the synthesized CsBr nanocrystals. In this system, the aqueous phase can be essentially separated from the hexane phase, carrying away excess Pb. 2+ It reacts with other byproduct salts, but the synthesized CsPbBr3 nanorods are highly unstable. (Adv. Mater. Technol. 2022, 7, 2200131) Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing all-inorganic CsPbBr3 perovskite nanorods with controllable morphology.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: Cs2CO3 is dried with octadecene and oleic acid under a nitrogen atmosphere until Cs2CO3 is completely dissolved to obtain a Cs-Oleate (Cs-OA) solution for later use;

[0009] The obtained Cs-Oleate (Cs-OA) solution was heated;

[0010] ZnBr2, octadecene, oleic acid, and oleylamine were dissolved under vacuum. After the mixed solution became clear and free of precipitate, nitrogen gas was used to replace the vacuum, and heated Cs-Oleate (Cs-OA) solution was added to initiate the reaction. The reaction was immediately cooled in an ice-water bath. The mixture was then centrifuged for the first time, leaving a precipitate. The remainder was dispersed in hexane and centrifuged a second time. The CsBr nanocrystals in the supernatant were then used as the precursor.

[0011] Anhydrous toluene, PbBr2, oleic acid and oleylamine were mixed and stirred until PbBr2 was completely dissolved to obtain a PbBr2 ligand solution.

[0012] PbBr2 ligand solution was added to the prepared CsBr nanocrystal precursor, and then ultrapure water was added and stirred to obtain CsPbBr3 perovskite nanorods.

[0013] In a preferred embodiment of the preparation method described in this invention, the mass ratio of Cs2CO3 to octadecene and oleic acid is 13 mg: 3 ml: 0.1 ml.

[0014] In a preferred embodiment of the preparation method described in this invention, the temperature is 110°C under a nitrogen atmosphere.

[0015] In a preferred embodiment of the preparation method described in this invention, the mass ratio of ZnBr2, octadecene, oleic acid and oleylamine is 20mg:2ml:0.2ml:0.2ml.

[0016] As a preferred embodiment of the preparation method described in this invention, the mass ratio of the CsBr nanocrystal solution, the PbBr2 ligand solution, and the ultrapure water is 1 ml: 0.5 ml: 5 μl.

[0017] In a preferred embodiment of the preparation method described in this invention, the ratio of anhydrous toluene, PbBr2, oleic acid and oleylamine is 5 ml: 0.188 mmol: 0.5 ml: 0.5 ml.

[0018] As a preferred embodiment of the preparation method described in this invention, the ratio of PbBr2 to CsBr nanocrystal precursor is 0.5 ml: 1 ml.

[0019] As a preferred embodiment of the preparation method of the present invention, the vacuum conditions include a temperature of 100°C and a dissolution time of ≥60 min.

[0020] As a preferred embodiment of the preparation method of the present invention, the Cs-Oleate (Cs-OA) solution obtained in step (1) is heated to a temperature of 150°C.

[0021] In a preferred embodiment of the preparation method described in this invention, the centrifugation is performed at a speed of 10,000 to 11,000 rpm for 8 to 10 minutes.

[0022] Beneficial effects of this invention:

[0023] (1) This invention achieves efficient and controllable preparation of all-inorganic CsPbBr3 perovskite nanorods by changing the ratio of water to oleic acid / oleylamine ligands, and the obtained nanorod solution has a good anisotropy value, which has good application prospects in the optoelectronic field.

[0024] (2) The product prepared by the method of the present invention has the morphology of a nanorod and has good dispersibility, with an average length of 100 nm and an average diameter of 20 nm.

[0025] (3) The PbBr2 and CsBr precursors required by this invention can be prepared in advance and have a very long shelf life, which greatly improves the synthesis efficiency of all-inorganic perovskite nanocrystals.

[0026] (4) The raw materials required for this invention are simple and readily available, the reaction conditions are mild, the operation is simple and efficient, no experimental conditions such as high temperature and inert atmosphere protection are required, and the preparation cost is low, making it suitable for large-scale industrial production. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0028] Figure 1 These are transmission electron microscope (TEM) images of CsPbBr3 perovskite nanorods prepared in Example 1 of this invention at different magnifications, wherein (a) is a TEM image with a 100 nm scale and (b) is a TEM image with a 10 nm scale.

[0029] Figure 2 This is a nanorod width distribution diagram of the CsPbBr3 perovskite nanorods prepared in Example 1 of the present invention.

[0030] Figure 3 The image shows the length distribution of the CsPbBr3 perovskite nanorods prepared in Example 1 of this invention.

[0031] Figure 4 The absorption spectrum and photoluminescence (PL) spectrum of the CsPbBr3 perovskite nanorods prepared in Example 1 of this invention are shown.

[0032] Figure 5 The X-ray diffraction pattern of the CsPbBr3 perovskite nanorods prepared in Example 1 of this invention.

[0033] Figure 6 The graph shows the PL decay curve of the CsPbBr3 perovskite nanorods prepared in Example 1 of this invention.

[0034] Figure 7 The image shows the in-situ PL curve of the CsPbBr3 perovskite nanorods prepared in Example 1 of this invention.

[0035] Figure 8 The anisotropy test of the CsPbBr3 perovskite nanorods prepared in Example 1 of the present invention is shown in (a) as a schematic diagram of anisotropy detection; (b) as PL spectrum measurement of long CsPbBr3 nanorods at different angles; and (c) as the anisotropy values ​​(R) of CsPbBr3 nanocrystals, short and long CsPbBr3 nanorods.

[0036] Figure 9 This is a transmission electron microscope (TEM) image of the CsPbBr3 perovskite nanorods prepared in Example 2 of this invention.

[0037] Figure 10 This is a transmission electron microscope (TEM) image of the CsPbBr3 perovskite nanorods prepared in Example 3 of this invention.

[0038] Figure 11 This is a transmission electron microscope (TEM) image of the CsPbBr3 perovskite nanorods prepared in Example 4 of this invention.

[0039] Figure 12 This is a transmission electron microscope (TEM) image of the CsPbBr3 perovskite nanorods prepared in Example 5 of this invention. Detailed Implementation

[0040] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0041] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0042] 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 phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0043] Table 1

[0044]

[0045] Example 1

[0046] This invention provides a method for preparing all-inorganic CsPbBr3 perovskite nanorods with controllable morphology:

[0047] (1) Preparation of Cs-Oleate (Cs-OA) solution: 13 mg Cs2CO3, 2 ml octadecene, and 0.1 mL oleic acid were placed into a 50 ml three-necked flask and dried under N2 atmosphere at 110 °C for 60 min until Cs2CO3 was completely dissolved to obtain Cs-Oleate (Cs-OA) solution for later use.

[0048] (2) Synthesis of spherical CsBr nanocrystals: 20 mg ZnBr2 was dissolved in a 50 mL three-necked flask, and 3 mL octadecene, 0.2 mL oleic acid, and 0.2 mL oleylamine were added. The mixture was heated under vacuum at 100 °C for at least 60 min. After the ZnBr2 solution became clear and free of precipitate, the Cs-Oleate (Cs-OA) solution obtained in step (1) was heated to 150 °C, and N2 gas was used instead of vacuum. The prepared ZnBr2 solution was then rapidly injected for 5 min, and the reaction was immediately cooled in an ice-water bath. The resulting product was centrifuged twice at 10,000 rpm for 8 min each time. The precipitate was retained after the first centrifugation, and the remainder was dispersed in 5 mL hexane and centrifuged again. The large-sized CsBr nanocrystals were discarded again, and the CsBr nanocrystals of suitable size in the supernatant were then used as precursors.

[0049] (3) Preparation of PbBr2 ligand solution: Anhydrous toluene (5 mL), PbBr2 (0.188 mmol), OA (0.5 mL), and OLA (0.5 mL) were added to a flask. The solution was stirred at 100 °C until PbBr2 was completely dissolved to obtain the PbBr2 ligand solution.

[0050] (4) Synthesis of CsPbBr3 nanorods: The prepared CsBr nanocrystal precursor (1 ml) was gently injected into a 5 ml bottle. Then, PbBr2 ligand solution (0.5 ml) was added directly, and finally ultrapure water (5 μl) was added. The mixture was stirred under magnetic stirring to obtain CsPbBr3 perovskite nanorods.

[0051] Example 2

[0052] The difference from Example 1 is that the ultrapure water in step (4) is 3 μl.

[0053] Example 3

[0054] The difference from Example 1 is that the ultrapure water in step (4) is 1 μl.

[0055] Example 4

[0056] The difference from Example 1 is that in step (3), both oleic acid and oleylamine are 0.25 mL.

[0057] Example 5

[0058] The difference from Example 1 is that in step (3), both oleic acid and oleylamine are 0.125 mL.

[0059] Example 6

[0060] For Example 1, the absorption spectrum was detected under illumination by a light source (Oceaninsight, DH-2000-BAL), and the PL was measured under 365nm excitation (Oceaninsight, L365A). All data were recorded using a fluorescence spectrophotometer (Oceaninsight QEPRO, USA).

[0061] Two linear polarizers were introduced into the excitation and emission channels of the OceanInsight spectrometer. Optical anisotropy was determined by a series of PL scans using the arrangement of the vertical and horizontal polarizers in the excitation and emission channels.

[0062] Anisotropic luminescent nanoparticles, such as rod-shaped particles, exhibit polarization in absorption and emission due to the inhomogeneity of the electric field intensity along different dimensional directions. We investigated the optical anisotropy of colloidal CsPbBr3 by measuring a series of PL spectra using vertically and horizontally oriented polarizers with different configurations placed in the excitation and emission channels of a PL spectrometer. ∥ and I ⊥ This is used to represent the intensity of light emitted with polarization parallel and perpendicular to the excitation polarization. These two parameters are related as a ratio, defined as I. ∥ / I ⊥ .

[0063] For CsPbBr3 nanocubes, I ∥ / I ⊥The value equals 1 because the emission intensity is the same along each axis of symmetry (ignoring any inherent instrument polarization sensitivity). For a long NR structure, the emission along the long axis will be higher than the emission along the transverse axis. The anisotropy value (R) at different wavelengths is calculated as shown in equation (1):

[0064]

[0065] like Figure 1 As shown in figure a, transmission electron microscopy (TEM) revealed that the obtained CsPbBr3 nanorods were uniformly dispersed nanorod products. High-resolution transmission electron microscopy (HRTEM) and corresponding fast Fourier transform (FFT) images are also included. Figure 1 b) indicates that the CsPbBr3 nanorods are cubic single crystals with a measured lattice spacing of approximately 0.29 nm, growing along the cubic phase

[001] direction.

[0066] like Figures 2-3 As shown, by statistically analyzing the dimensions of approximately 100 samples, a histogram of the length and width distribution of CsPbBr3 nanorods was obtained, with an average length of 100 nm and an average diameter of 20 nm.

[0067] The photoluminescence (PL) spectrum and UV-Vis absorption spectrum of CsPbBr3 nanorods in n-hexane are as follows: Figure 4 As shown, the absorption edge of the CsPbBr3 nanorods exhibits a bulge at 510 nm, indicating that the light absorption band consists of continuous absorption and peak absorption, corresponding to exciton absorption. The photoluminescence (PL) spectrum of the CsPbBr3 nanorods shows a distinct red emission peak centered at 522 nm. Bulk CsPbBr3 typically shows strong green emission at 512 nm, but the luminescence of our synthesized CsPbBr3 nanorods differs significantly from that of small-sized bulk CsPbBr3. The PL emission with a redshift of 10 nm can be attributed to the quantum confinement effect within the nanorods. The full width at half maximum (FWHM) is 20 nm, similar to the PL peak of high-quality CsPbBr3 nanocrystals.

[0068] The most obvious difference between the cubic and orthorhombic phases of CsPbBr3 nanocrystals lies in the peak position at 30° in their XRD patterns. A single peak indicates a cubic phase, while an orthorhombic peak indicates an orthorhombic phase. The X-ray diffraction (XRD) patterns of CsPbBr3 nanorods are shown below. Figure 5As shown, the corresponding XRD peaks confirm the final formation of cubic CsPbBr3 nanorods (PDF comparison card 01-072-7929). No obvious peaks belonging to Cs4PbBr6 were observed, indicating a high yield of the chemical synthesis reaction. Analysis of the XRD patterns of the products during the reaction process revealed a rhombic Cs4PbBr6 peak appearing in the middle stage of the reaction (PDF comparison card 01-073-2478).

[0069] Figure 6 The time-resolved photon lifetime (PL) decay of CsPbBr3 nanorods of different sizes is shown, exhibiting a predominantly exponential decay pattern. The time required for the signal to decrease to 1 / e of its initial intensity defines the average PL lifetime. The PL lifetime in nanorods can be attributed to two main reasons. First, compared to long nanorods, nanocrystals experience greater axial confinement and Coulomb forces, increasing the probability of electron-hole recombination and resulting in the shortest radiative recombination lifetime for nanocrystals. Second, the variation in nonradiative lifetime is likely driven by the rate at which excitons encounter surface traps. The presence of water during the reaction inevitably damages the surface ligands of the sample, leading to an increase in surface traps and resulting in the shortest nonradiative recombination lifetime for long nanorods. Therefore, the average PL lifetime of long nanorods is relatively small compared to nanocrystals.

[0070] according to Figure 7 The evolution of the PL spectrum during the rapid formation of CsPbBr3 nanorods shows that the initial peak of the reaction solution also appears at around 490 nm. The precursor reaches the first peak at 45 s during the reaction, with a wavelength around 510 nm. However, as the reaction continues, the peak intensity gradually decreases between 45 s and 60 s, but then rises again between 45 s and 85 s and reaches a stable maximum value around 522 nm.

[0071] The emission polarization device of CsPbBr3 nanocubes, such as Figure 8 As shown in Figure a, the spectrum is characteristically centered at R=0, indicating that the CsPbBr3 nanocrystals are anisotropic. In contrast, both short and long CsPbBr3 nanorods exhibit anisotropy in solution, with the highest R values ​​measured near the wavelength of their PL peak. With increasing wavelength, the anisotropy R of the nanocrystal-short nanorod combination reaches a maximum of 0.1 in the 475–500 nm range. Figure 8 (b) and remains at this value, consistent with the emission peak at 516 nm, then slightly decreases to 0.07 in the 520–540 nm range. For long nanorods, the anisotropy steadily increases from 475 nm to 520 nm, reaching 0.15 at the emission peak at 520 nm. Figure 8c). For nanorod particles dispersed in solution, this anisotropy value demonstrates the applicability of the perovskite nanorods prepared in this paper as potential linearly polarized emission sources. We observed that the difference in anisotropy values ​​between CsPbBr3 nanocubes and short and long nanorods is attributed to their differences in aspect ratio: long nanorods exhibit the largest anisotropy among these samples due to the greater difference in transition dipole moments between longitudinal and transverse orientations.

[0072] The physicochemical properties of perovskite nanomaterials are size-dependent, and nanocrystals of different sizes can meet the application requirements of materials in different scenarios. To further investigate the effect of water on the morphology and luminescence properties of CsPbBr3 nanorods, we added different amounts of water during the reaction process. When only 1 μl of water was added, the resulting product exhibited well-formed nanocubes (length and diameter of the nanorods). Figure 10 At this point, water helps lower the activation energy. However, due to the extremely low water content, insufficient contact with the CsBr nanocrystal surface limits the extent of surface ligand disruption. Therefore, directional growth is not promoted, resulting in the formation of CsPbBr3 nanocrystals. However, when the water content is increased to 3 μl, the product transforms into a combination of nanocrystals and short nanorods. Figure 9 ).

[0073] To further investigate the growth mechanism of CsPbBr3 nanorods, this invention added different amounts of oleic acid and oleylamine ligands to dissolve PbBr2, and then added 5 μl of ultrapure water to participate in the reaction. When the amount of water added was kept constant at 5 μl, while the amount of the precursor PbBr2 ligand was varied, the morphology of the resulting product showed a striking similarity to that obtained by varying the amount of water. When the ligand amount was halved to 25 μl, the product was still nanorods with a width of 20 nm, but the lengths varied, resulting in nanorods with uneven lengths. Figure 11 If the ligand amount is reduced to one-quarter, we find that all the resulting products are nanocubes with an average size of 20 nm. Figure 12 These results clearly demonstrate the crucial roles of oleic acid and oleylamine ligands in the formation of CsPbBr3 nanorods. Similar to the experiments with varying water content, the width distribution of all nanorods remained remarkably uniform (20 nm) regardless of variations in nanorod length.

[0074] Comparative Example 1

[0075] The difference from Example 1 is that ultrapure water is not added in step (4).

[0076] Experimental results showed that the experiment failed in regulating the ligands in the precursor PbBr2.

[0077] The product obtained by the above-mentioned preparation method of all-inorganic CsPbBr3 perovskite nanorods has the morphology of nanorods and good dispersibility, with an average length of 100 nm and an average diameter of 20 nm. It does not require experimental conditions such as high temperature and inert atmosphere protection, and the preparation cost is low, making it suitable for large-scale industrial production.

[0078] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing all-inorganic CsPbBr3 perovskite nanorods with controllable morphology, characterized in that: include, Cs2CO3 was dried with octadecene and oleic acid under a nitrogen atmosphere until Cs2CO3 was completely dissolved to obtain a Cs-Oleate solution for later use. The obtained Cs-Oleate solution was heated; ZnBr2, octadecene, oleic acid and oleylamine were dissolved under vacuum. After the mixed solution became clear and free of precipitate, nitrogen gas was used to replace the vacuum, and heated Cs-Oleate solution was added to carry out the reaction. The reaction was immediately cooled in an ice-water bath after the reaction. The first centrifugation was then performed, leaving a precipitate. The remainder was then dispersed in hexane and centrifuged a second time. The CsBr nanocrystal precursor in the supernatant was then collected. Anhydrous toluene, PbBr2, oleic acid and oleylamine were mixed and stirred until PbBr2 was completely dissolved to obtain a PbBr2 ligand solution; PbBr2 ligand solution was added to CsBr nanocrystal precursor, and then ultrapure water was added and stirred to obtain CsPbBr3 perovskite nanorods. The ratio of Cs2CO3 to octadecene and oleic acid is 13mg:3ml:0.1ml; The ratio of ZnBr2, octadecene, oleic acid, and oleylamine is 20mg:2ml:0.2ml:0.2ml; The ratio of the CsBr nanocrystal precursor, PbBr2 ligand solution, and ultrapure water is 1 ml: 0.5 ml: 5 μl. The ratio of anhydrous toluene, PbBr2, oleic acid, and oleylamine was 5 ml: 0.188 mmol: 0.5 ml: 0.5 ml. The ratio of PbBr2 to CsBr nanocrystal precursors was 0.5 ml: 1 ml.

2. The method as described in claim 1, characterized in that: The temperature is 110°C under nitrogen atmosphere.

3. The method as described in claim 1, characterized in that: The vacuum conditions include a temperature of 100°C and a dissolution time of ≥60 min.

4. The method as described in claim 1, characterized in that: The obtained Cs-Oleate solution is heated to a temperature of 150°C.

5. The method as described in claim 1, characterized in that: The centrifugation is performed at a speed of 10,000 to 11,000 rpm for 8 to 10 minutes.

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