Method for preparing spherical-like superlattice microcavity from self-assembled rhombic dodecahedron perovskite nanocrystals

Abstract

A method for preparing self-assembled spherical superlattice microcavity from synthetic rhombic dodecahedron nanocrystals, the method comprises the following steps: prolonging annealing time through hot injection method to obtain rhombic dodecahedron CsPbBr3 nanocrystals with good monodispersity, dispersing the nanocrystals in toluene solution after centrifugal separation and purification, dropping appropriate diluted nanocrystal solution on a substrate, slowly evaporating at low temperature, and self-assembling the rhombic dodecahedron nanocrystals in the solution into superlattice with regular morphology structure under the interaction between ligands and ligands and between solvent and ligands. The size of the self-assembled superlattice structure is approximately several hundred nanometers to several microns. The regular rhombic dodecahedron nanocrystals have good application prospect in the field of photocatalysis and display due to their weak size limitation effect and multi-faceted nature; meanwhile, the spherical superlattice has a high packing factor due to the close packing of its structure, and can form a microcavity as an optical feedback surface in combination with the regular geometric morphology of the self-assembled superlattice structure.

Description

Technical Field

[0001] This invention relates to the preparation of rhombic dodecahedral nanocrystals and perovskite microcavities, which differs from traditional cubic perovskite nanocrystals. In particular, it is a method for preparing spherical superlattice microcavities by self-assembling rhombic dodecahedral CsPbBr3 nanocrystals. This synthesis process is simple to operate and highly reproducible, and also has a relatively low laser radiation threshold. It is of great significance for realizing low-threshold cavity-enhanced superfluorescence and the application of colloidal quantum dots in the laser field. Background Technology

[0002] Due to the rapid development of laser technology and the low-cost synthesis of nanocrystals, combined with their ease of integration with semiconductor devices in existing microelectronics, semiconductor lasers based on processable solutions have become a long-term challenge and research hotspot for next-generation displays, light sources, and communication technologies.

[0003] Metal halide perovskite quantum dots have become an exciting class of quantum emitters due to their excellent optical properties: large oscillator strength, high quantum yield, and long coherence time. However, current cavity-enhanced superfluorescence achieved with perovskite quantum dots still suffers from a high gain threshold. The cubic nanocrystals of long-chain organic ligands, due to their crystal structure and defects, also exhibit a high gain threshold, which severely hinders the further development of cavity-enhanced superfluorescence.

[0004] To address the aforementioned issues, we introduced polyhedral nanocrystal building blocks and synthesized new ligands using an improved thermal injection method to stabilize the new faces, thereby forming row-stable dodecahedral nanocrystals. These rhombic dodecahedral nanocrystals, exhibiting lower nonradiative recombination, were then self-assembled into a superlattice structure serving as an optical microcavity. This integrated the gain medium and resonant cavity, improving the coupling problem between quantum dots and the optical cavity in semiconductor lasers and alleviating the pain point of excessively high gain thresholds. This has significant implications for the application of quantum dot lasers in quantum light sources and communications. Summary of the Invention

[0005] The purpose of this invention is to improve upon existing technologies by providing a method for synthesizing faceted perovskite nanocrystals to self-assemble into spherical perovskite superlattices. The method synthesizes rhombic dodecahedral nanocrystals with good monodispersity and uniform, regular shape; the preparation process is simple and highly reproducible, and the self-assembled superlattice structure is regularly ordered; furthermore, compared to oleic acid-oleylamine modified nanocrystals, it exhibits a lower Auger recombination rate, resulting in a lower gain threshold when used in optical microcavities, which is more beneficial for the development and application of laser materials.

[0006] The technical solution of the present invention is as follows:

[0007] A method for preparing spherical superlattice microcavities by self-assembling rhombic dodecahedral perovskite nanocrystals, characterized by comprising:

[0008] Step 1. Preparation of cesium oleate precursor solution: Cesium carbonate powder, oleic acid and octadecene are mixed evenly, stirred and heated until cesium carbonate dissolves. The mixture is then heated to 150°C, annealed and cooled naturally to obtain cesium oleate precursor solution.

[0009] Step 2. Preparation of rhombic dodecahedral CsPbBr3 colloidal quantum dots: A certain ratio of lead oxide and benzoyl bromide were added to a certain amount of oleic acid and octadecene, stirred and mixed, and the mixture was heated to 220°C. A certain amount of oleylamine was injected, and after annealing, the solution turned clear yellow. Then, the temperature was lowered to 165-220°C, and the cesium oleate precursor solution was injected. After annealing, a crude solution of rhombic dodecahedral CsPbBr3 colloidal quantum dots was obtained.

[0010] Step 3. Purification of rhombic dodecahedral CsPbBr3 colloidal quantum dots: The crude solution of rhombic dodecahedral CsPbBr3 colloidal quantum dots is purified. The precipitate after centrifugation is dispersed in toluene solvent and an appropriate amount of methyl acetate is added. Centrifugation is performed again, and the process is repeated twice. The precipitate is dissolved in a certain amount of toluene solvent, placed in a sample bottle, and stored at low temperature for at least 24 hours. The supernatant in the sample bottle is the superlattice quantum dot solution.

[0011] Step 4. Preparation of quasi-spherical superlattice microcavities: Take an appropriate amount of the superlattice quantum dot solution, dilute and disperse it in toluene, drop it into a tube, place the substrate in the tube, and store it at low temperature in the dark. The substrate surface and the nanocrystal solution form a solid-liquid interface, and the quasi-spherical superlattice microcavities are obtained by self-assembly as the solvent evaporates.

[0012] Preferably, step 1, the preparation of cesium oleate precursor solution, specifically involves: weighing 1.2 mmol of cesium carbonate powder, 2 ml of oleic acid and 18 ml of octadecene, mixing them evenly, stirring and heating the mixture until the cesium carbonate is completely dissolved, then raising the temperature to 150°C and annealing for a certain time before naturally cooling to obtain cesium oleate precursor solution.

[0013] Preferably, in step 3, the molar ratio of lead oxide to benzoyl bromide is 1:3.

[0014] Preferably, in step 2, the volume ratio of oleic acid, octadecene, and oleylamine is 2:10:1.

[0015] Preferably, both steps 1 and 2, which involve heating, are performed in a nitrogen atmosphere.

[0016] Preferably, the annealing time after injecting oleylamine in step 2 is 11-15 min, and the annealing time after injecting cesium oleate precursor fluid is 10-15 min.

[0017] Preferably, in step 4, the amount of solution dropped into the tube is 100 ml, the deposition wafer is a single crystal silicon wafer, and the low-temperature deposition temperature is 6-8℃.

[0018] A method for preparing spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals is described. The perovskite nanocrystals used for self-assembly have a regular dodecahedral morphology, with a particle size of 13-15 nm, exhibiting monodispersity and size uniformity. The self-assembled superlattice microcavities have a spherical morphology, a regular and ordered internal structure, a high packing factor, and a diameter adjustable between 400 nm and 4 μm. Upon excitation, they can generate laser light with a low threshold.

[0019] Compared with the prior art, the technical effects of the present invention are as follows:

[0020] This invention modifies the bromine and lead sources used to synthesize quantum dots. Through a series of nucleophilic substitution reactions, the bromine source (benzoyl bromide) releases HBr, initially forming a primary ammonium bromide with oleylamine. With prolonged annealing, tertiary ammonium ions are generated, stabilizing the new facets and leading to the formation of dodecahedral nanocrystals. In the preparation of rhombic dodecahedral quantum dots, the injection temperature of oleylamine and the precursor solution, as well as the annealing time and purification steps, all affect the size and morphology of the rhombic dodecahedral nanocrystals. Changes in the assembly units lead to changes in the assembled superlattice structure. The solvent type, evaporation time, and temperature during the self-assembly process also affect the regularity and morphology of the superlattice structure, ultimately impacting its quality. Therefore, the synthesis conditions should be carefully controlled to form a superlattice structure of ideal size and regularity.

[0021] The final three-dimensional all-inorganic perovskite quantum dot self-assembled spherical superlattice microcavities have regular morphology, orderly arrangement, and relatively smooth surface, with sizes adjustable from hundreds of nanometers to several micrometers.

[0022] This invention provides a self-assembly method for obtaining a size-tunable spherical superlattice microcavity structure. The fabrication process is simple, low-cost, and highly reproducible. The resulting superlattice is composed of long-range ordered, closely packed quantum dots, exhibiting a high gain coefficient and low nonradiative recombination. It can simultaneously serve as a gain medium and a resonant cavity, enabling high-quality, low-threshold single-mode laser. Attached Figure Description

[0023] Figure 1 The images shown are TEM images of the rhombic dodecahedral CsPbBr3 quantum dots of this invention. a) shows the morphology of a monodisperse rhombic dodecahedral quantum dot; b) shows a high-resolution transmission electron microscope image of a single rhombic dodecahedral quantum dot.

[0024] Figure 2This is a SEM image of the self-assembled spherical superlattice microcavity of rhombic dodecahedral CsPbBr3 perovskite quantum dots according to the present invention.

[0025] Figure 3 These are TEM images of self-assembled spherical superlattice microcavities of rhombic dodecahedral CsPbBr3 perovskite quantum dots of different sizes according to the present invention. a is 400 nm; b is 800 nm; c is 3 μm.

[0026] Figure 4 This is a graph showing the power variation of single-mode lasing in a spherical superlattice microcavity assembled from rhombic dodecahedral CsPbBr3 perovskite quantum dots according to the present invention.

[0027] Figure 5 This is a comparison of threshold curves for the self-assembled spherical superlattice microcavity of rhombic dodecahedral CsPbBr3 perovskite quantum dots and the self-assembled superlattice microcavity of cubic hexahedral perovskite quantum dots in this invention. The upper part shows the self-assembled spherical superlattice microcavity of rhombic dodecahedral CsPbBr3 perovskite quantum dots with a threshold of 15.5 μJ / cm². -2 The lower part is a cubic hexahedral perovskite quantum dot self-assembled superlattice microcavity with a threshold of 31.8 μJ / cm². -2 . Detailed Implementation

[0028] To further illustrate the fabrication of a self-assembled spherical superlattice microcavity from rhombic dodecahedral CsPbBr3 perovskite quantum dots, an example is provided demonstrating the implementation of the present invention, with a detailed implementation process outlined.

[0029] Example 1

[0030] (1) Weigh 200 mg of cesium carbonate powder, 1 ml of oleic acid and 8 ml of octadecene and add them to a three-necked flask and mix them evenly. Under nitrogen protection, continuously stir and heat the mixture to 120°C and hold for 30 min. Then heat it to 150°C and hold for 10 min. Then cool it naturally to room temperature as a cesium oleate precursor.

[0031] (2) Weigh 0.4 mmol lead oxide, 1.2 mmol benzoyl bromide, 2 ml oleic acid and 10 ml octadecene into a three-necked flask, stir continuously and heat the mixture to 120 °C and maintain it under a nitrogen atmosphere for 30 min. Then raise the temperature to 220 °C and inject 1 ml oleylamine. After annealing for 11 min, the solution changes from orange-red to clear yellow. Then lower the temperature to 170 °C and quickly inject 1 ml cesium oleate precursor solution. After annealing for 15 min, cool to room temperature in an ice-water bath to obtain a crude solution of rhombic dodecahedral CsPbBr3 colloidal quantum dots.

[0032] (3) The crude solution was purified by centrifugation. The centrifuge speed was set to 8500 rpm and the time was set to 10 min. The precipitate after centrifugation was dispersed in hexane solvent and an appropriate amount of methyl acetate was added (the ratio of solvent to methyl acetate was 4:1). The centrifuge speed was set to 9000 rpm and the time was 5 min. The precipitate was dissolved in a certain amount of toluene solvent and placed in a sample bottle for low-temperature storage. After 24 h, the supernatant was taken with a pipette to obtain the quantum dot solution for preparing the superlattice.

[0033] (4) Take 10 μL of the quantum dot solution prepared above and drop it onto the ultrathin carbon support film. Observe the morphology by TEM. Figure 1 As shown in Figure a, the obtained dodecahedral nanocrystals have an edge length of approximately 14 nm, exhibiting good monodispersity and size uniformity; Figure 1 The high-resolution transmission electron microscope image shown in b reveals that the synthesized rhombic dodecahedral quantum dots have a well-formed shape.

[0034] (5) Use a pipette to take an appropriate amount of colloidal solution and dilute it in toluene to obtain a quantum dot solution with a concentration of 15 mg / ml. Take 100 μL of the diluted solution and drop it into a tube. Place the substrate into the tube and store the sample at a low temperature of 6-8℃ in the dark. The substrate and the nanocrystalline solution form a solid-liquid interface. As the toluene slowly evaporates, a spherical superlattice microcavity structure gradually forms on the substrate.

[0035] (6) Morphological observation of the spherical superlattice microcavity using SEM, such as... Figure 2 As shown, the quantum dots are closely packed together to form a spherical self-assembled structure with a high stacking factor. The shape is relatively regular, and the diameter of the spherical superlattice microcavity is approximately 3.5 μm.

[0036] Example 2

[0037] This embodiment mainly investigates the effects of reaction materials, oleylamine injection temperature, annealing time, Cs precursor injection temperature, quantum dot solution concentration, evaporation time, and evaporation temperature on the formation of spherical superlattice microcavities during the self-assembly of perovskite quantum dots into spherical superlattice microcavities. The specific experimental steps are the same as in Example 1, except that the reaction materials, oleylamine injection temperature, annealing time, Cs precursor injection temperature, quantum dot solution concentration, evaporation time, and evaporation temperature were varied. Specific experimental parameters are shown in Table 1.

[0038] Table 1. Experimental conditions for preparing the above-mentioned perovskite quantum dot self-assembled spherical superlattice microcavities:

[0039]

[0040] Experimental results show that changes in the bromine and lead sources affect the synthesis of quantum dots. Lead halides more readily synthesize cubic hexahedral nanocrystals, while benzoyl bromide and lead oxide can synthesize rhombic dodecahedral nanocrystals. Changes in the morphology of the nanocrystal building blocks used for assembly affect the morphology of the assembled superlattice microcavity structure. Simultaneously, the injection temperature of oleylamine and the first annealing time also influence the morphology of the nanocrystals. Oleylamine injection needs to be carried out at 220℃, and the first annealing time needs to be greater than 10 minutes to synthesize rhombic dodecahedral nanocrystals. Otherwise, the synthesized nanocrystals will have a wide size distribution and diverse morphologies, leading to unsatisfactory assembly results. The injection temperature of the Cs precursor solution also affects the size of the synthesized quantum dots, thus affecting the size of the assembled superlattice microcavity structure. The concentration of the assembly solution, the evaporation time, and the temperature all affect the quality and morphology of the assembled structure. Under suitable assembly concentrations (15-20 mg / ml), extending the solution evaporation time by lowering the temperature makes it easier to obtain tightly assembled, regular structures.

[0041] By controlling and altering the assembly factors described above, we can control the diameter of the spherical superlattice microcavity structure. The microcavity structure was then transferred onto an ultrathin carbon support film, and its morphology was observed using TEM. Figure 3 As shown in Figures a, b, and c, the dimensions of the spherical superlattice microcavity structures are 400 μm, 800 μm, and 3 μm, respectively. By changing the assembly influencing factors, the dimensions of this spherical superlattice microcavity structure can be controlled between 400 and 4 μm.

[0042] Application Examples:

[0043] This example examines whether the CsPbBr3 perovskite quantum dot self-assembled spherical superlattice sample obtained in Example 1 can be used as a laser microcavity to generate lasing under pumping.

[0044] The experimental setup for this example is an ultrafast transient spectrometer (model HR Evolution & FLS980). The specific experimental steps are as follows: First, the single-crystal silicon wafer with the deposited sample is placed on the sample stage of the micro-fluorescence spectrometer. The stage height is adjusted, and a 50x lens is selected. The CsPbBr3 spherical superlattice structure is located under the microscope. Then, a 400nm femtosecond laser (model Libra-USP-10k-HE) is turned on and introduced into the spectrometer. After adjusting the microscope lens and focusing the laser spot, spectral detection is performed. The fluorescence spectrum of the sample can be obtained under low-power pumping. Next, by gradually increasing the excitation power, single-mode lasing can be obtained in the superlattice microcavity. The experimental results are as follows: Figure 4 As shown, Figure 4The graph shows the single-mode lasing versus power in a self-assembled superlattice microcavity of rhombic dodecahedral CsPbBr3 perovskite quantum dots. The sharp, narrow peaks in the graph demonstrate the presence of laser light, proving that the obtained CsPbBr3 perovskite quantum dot self-assembled spherical superlattice sample can be used as a laser microcavity to generate lasing under pumping.

[0045] Based on the conditions in item 1 of Table 1, we also assembled a superlattice structure using traditional cubic hexahedral nanocrystals and compared it with a spherical superlattice microcavity assembled using rhombic dodecahedral quantum dots. The experimental results are as follows. Figure 5 As shown. Figure 5 This is a comparison of threshold curves for two microcavity structures. The upper part shows the self-assembled spherical superlattice microcavity of rhombic dodecahedral CsPbBr3 perovskite quantum dots according to the present invention, with a measured threshold of 15.5 μJ / cm². -2 The lower part is a cubic hexahedral perovskite quantum dot self-assembled superlattice microcavity, with a measured threshold of 31.8 μJ / cm². -2 This invention reduces the lasing threshold by about 50%, resulting in superior optical performance.

Claims

1. A method for preparing spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals, characterized in that, include: Step 1. Preparation of cesium oleate precursor solution: Cesium carbonate powder, oleic acid and octadecene are mixed evenly, stirred and heated until cesium carbonate dissolves. The mixture is then heated to 150°C, annealed and cooled naturally to obtain cesium oleate precursor solution. Step 2. Preparation of rhombic dodecahedral CsPbBr3 colloidal quantum dots: A certain ratio of lead oxide and benzoyl bromide were added to a quantitative amount of oleic acid and octadecene, stirred and mixed, and the mixture was heated to 220°C. A quantitative amount of oleylamine was injected, and after annealing, the solution turned clear yellow. The annealing time after injecting oleylamine in Step 2 was greater than 10 min. Then, the temperature was lowered to 165-220°C, and the cesium oleate precursor solution was injected. Annealing was then performed to obtain a crude solution of rhombic dodecahedral CsPbBr3 colloidal quantum dots. Step 3. Purification of rhombic dodecahedral CsPbBr3 colloidal quantum dots: The crude solution of rhombic dodecahedral CsPbBr3 colloidal quantum dots is purified. The precipitate after centrifugation is dispersed in toluene solvent and an appropriate amount of methyl acetate is added. Centrifugation is repeated twice. The precipitate is dissolved in a certain amount of toluene solvent, placed in a sample bottle, and stored at low temperature for at least 24 hours. The supernatant in the sample bottle is the superlattice quantum dot solution. Step 4. Preparation of quasi-spherical superlattice microcavities: Take an appropriate amount of the superlattice quantum dot solution, dilute and disperse it in toluene, drop it into a tube, place the substrate in the tube, and store it in the dark at 6-8℃. The substrate surface and the nanocrystal solution form a solid-liquid interface, and the quasi-spherical superlattice microcavities are obtained by self-assembly as the solvent evaporates.

2. The method for preparing spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals according to claim 1, wherein step 1, the preparation of cesium oleate precursor solution, specifically comprises: weighing 200 mg of cesium carbonate powder, 1 ml of oleic acid and 8 ml of octadecene, mixing them evenly, stirring and heating the mixture until the cesium carbonate is completely dissolved, then raising the temperature to 150°C and annealing for a certain time, followed by natural cooling to obtain cesium oleate precursor solution.

3. The method for preparing spherical superlattice microcavities by self-assembling rhombic dodecahedral perovskite nanocrystals according to claim 1, wherein the molar ratio of lead oxide to benzoyl bromide in step 2 is 1:

3.

4. The method for preparing quasi-spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals according to claim 1, characterized in that... In step 2, the volume ratio of oleic acid, octadecene, and oleylamine is 2:10:

1.

5. The method for preparing quasi-spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals according to claim 1, characterized in that, Both steps 1 and 2, involving heating, are performed in a nitrogen atmosphere.

6. The method for preparing quasi-spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals according to claim 1, characterized in that, The annealing time after injecting oleylamine in step 2 is 11-15 minutes. The annealing time after injection of cesium oleate probiotic is 10-15 minutes.

7. The method for preparing quasi-spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals according to claim 1, characterized in that, In step 4, the amount of solution dropped into the tube is 100 μl, and the substrate is a single-crystal silicon wafer.

8. The method for preparing quasi-spherical superlattice microcavities using self-assembled rhombic dodecahedral perovskite nanocrystals according to claim 1, characterized in that, The perovskite nanocrystals used for self-assembly have a regular dodecahedral morphology, with a particle size of 13-15 nm, exhibiting monodispersity and size uniformity. The superlattice microcavities formed by self-assembly have a spherical morphology, with a regular and ordered internal structure, a high packing factor, and a diameter that is adjustable between 400 nm and 4 μm. After excitation, they can generate lasers with a low threshold.

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