Method for synthesizing all-inorganic lead halide perovskite nanocrystal through one-pot in-situ phase transformation and product prepared through method

Abstract

The method comprises the following steps: mixing cesium carbonate, lead halide, 1-octadecene and an organic ligand, then carrying out gradual heating, fully utilizing the solubility difference of raw materials under a low-temperature condition, firstly forming an intermediate phase Cs4PbX6 under the low-temperature condition, and carrying out one-pot in-situ phase transformation on the intermediate phase Cs4PbX6 to obtain the all-inorganic lead halide perovskite nanocrystal. And reacting the intermediate phase with gradually dissolved PbX2 at a relatively high temperature to form the CsPbX3 nanocrystal in situ. According to the invention, through the formation of the intermediate phase, the formation process of the CsPbX3 nanocrystal is delayed, the growth process of the nanocrystal is effectively regulated and controlled, and the perovskite nanocrystal with excellent fluorescence performance can be obtained. The method has the advantages of simple preparation process, cheap and easily available raw materials, mild reaction conditions, no need of inert protective atmosphere, good reproducibility, easy batch preparation and the like, and can promote large-scale preparation and commercial application of the perovskite nanocrystals.

Description

Technical Field

[0001] The present invention relates to the fields of nanoscience and technology and light-emitting display technology, and particularly relates to a method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition and a product obtained thereby. Background Art

[0002] As a new type of fluorescent material, all-inorganic lead halide perovskite (CsPbX3, X = Cl, Br, I) nanocrystals have the characteristics of high defect tolerance, large light absorption coefficient, high color purity, wide color gamut, and low preparation cost, and have great application potential in the fields of high-definition display, solar cells, photoelectric detection, etc. Since the research group of Professor M.V. Kovalenko at the Swiss Federal Institute of Technology in Zurich first synthesized CsPbX3 nanocrystals by the hot injection method in 2015, this type of material has made great progress in synthesis, performance regulation, photoelectric applications, etc., and has set off a research boom worldwide. The hot injection method is currently the most common method for synthesizing perovskite nanocrystals, and the obtained products have advantages such as high fluorescence quantum yield (~100%), high crystallinity, and good stability. However, in the hot injection synthesis process, usually strict experimental conditions are required, such as: inert gas protection, relatively high synthesis temperature, rapid cooling conditions to terminate the reaction, etc.; in addition, the nucleation and growth processes of nanocrystals strongly depend on the injection volume and speed of the precursors, resulting in poor repeatability of the method for synthesizing perovskite nanocrystals. The above problems not only increase the preparation cost of perovskite nanocrystals, but also increase the synthesis difficulty, which is not conducive to the large-scale preparation of such materials.

[0003] In recent years, although a series of new methods for preparing perovskite nanocrystals have been reported successively (such as: room temperature supersaturated recrystallization method, microwave heating method, ultrasonic assisted method, solvothermal method, etc.), due to the relatively high ionic nature of lead halide perovskite materials and the relatively low crystal formation energy, the nucleation and growth processes of such materials are extremely fast (usually completed within dozens of seconds), so it is difficult to effectively regulate their reaction kinetics, resulting in poor fluorescence performance of nanocrystals and large differences in the fluorescence performance of products synthesized in different batches, which seriously restricts the large-scale popularization and application of perovskite nanocrystals and hinders their actual application process. Therefore, exploring a simple, efficient, and controllable new strategy for preparing high-performance all-inorganic lead halide perovskite nanocrystals is of great significance for promoting their large-scale commercial applications. Summary of the Invention

[0004] The object of the present invention is to overcome the deficiencies of the prior art and provide a method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition. By means of the solubility difference of raw materials under low-temperature conditions, Cs4PbX6 nanocrystals are first synthesized; then the temperature is raised, and Cs4PbX6 reacts with gradually dissolved PbX2 to in-situ form CsPbX3 nanocrystals. Through the formation of the intermediate phase Cs4PbX6, the formation process of CsPbX3 nanocrystals is delayed, and the growth process of the nanocrystals is effectively regulated, which is conducive to obtaining lead halide perovskite nanocrystals with excellent fluorescence properties. Another object of the present invention is to provide a product prepared by the above preparation method.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition provided by the present invention includes the following steps:

[0007] (1) Cesium carbonate and lead halide are added to a flask according to a molar ratio of n Cs ∶n Pb = 1∶0.2 - 5, and 1-octadecene, an organic solvent, is added to form a mixed solution with a metal ion concentration of 0.02 - 1.00 mol / L; then, according to a volume ratio of organic acid∶organic amine∶1-octadecene = 0.01 - 0.5∶0.01 - 0.5∶1, the organic acid and the organic amine are added in sequence to obtain a mixed precursor solution;

[0008] (2) The mixed precursor solution is heated progressively. The progressive heating regime is to first heat at a temperature of 60 - 90 °C for 5 - 120 min, and then raise the temperature to 100 - 150 °C and react for 5 - 120 min to obtain an initial reaction solution;

[0009] (3) The initial reaction solution is naturally cooled to room temperature, and then after centrifugal washing, the obtained precipitate is dispersed in an organic solvent to obtain an all-inorganic lead halide perovskite nanocrystal solution.

[0010] Further, the lead halide in the present invention is one or a combination of lead bromide, lead chloride, and lead iodide. The organic acid is butyric acid, caprylic acid, lauric acid, or oleic acid, and the organic amine is butylamine, octylamine, dodecylamine, or oleylamine.

[0011] In the above solution, the organic solvent in step (3) of the present invention is n-hexane, toluene, xylene, or dichloromethane.

[0012] The product obtained by the method for synthesizing all-inorganic lead halide perovskite nanocrystals through the above-mentioned one-pot in-situ phase transition has a phase composition of CsPbX3 or a mixture of CsPbX3 and Cs4PbX6, where X is one or a combination of Cl, Br, and I.

[0013] The present invention has the following beneficial effects:

[0014] (1) By utilizing the characteristic that lead halide has a relatively low solubility in the reaction system under low-temperature conditions, the present invention first synthesizes the Cs4PbX6 intermediate phase, and then raises the reaction temperature to promote the dissolution of lead halide. At the same time, it triggers the reaction between Cs4PbX6 and PbX2 to in-situ form CsPbX3 nanocrystals. Through the formation of the intermediate phase, the formation process of CsPbX3 nanocrystals is delayed, effectively regulating the growth process of the nanocrystals, which is conducive to obtaining lead halide perovskite nanocrystals with a high quantum yield (up to 98.7%) and continuous tuning of the emission wavelength in the entire visible light region (400 - 700 nm), laying an important foundation for the controllable synthesis and optoelectronic applications of such materials.

[0015] (2) The present invention uses a one-pot method to prepare lead halide perovskite nanocrystals. By simply mixing and heating cesium carbonate, lead halide, solvent 1-octadecene, and ligand, perovskite nanocrystals can be obtained. The preparation process is simple, the raw materials are cheap and easily available, the reaction conditions are mild, and an inert protective atmosphere is not required. At the same time, this method has good reproducibility, is easy to prepare in batches, and is convenient for large-scale commercial applications. Description of the Drawings

[0016] The present invention will be further described in detail below in combination with examples and drawings:

[0017] Figure 1 is the TEM photo of the perovskite nanocrystals prepared in Example 1 of the present invention;

[0018] Figure 2 is the PL spectrum of the perovskite nanocrystals prepared in Example 1 and Example 2 of the present invention;

[0019] Figure 3 is the PLQY spectrum of the perovskite nanocrystals prepared in Example 2 of the present invention;

[0020] Figure 4 is the XRD spectrum of the perovskite nanocrystals prepared in Example 2 of the present invention;

[0021] Figure 5 is the XRD spectrum of the perovskite nanocrystals prepared in Example 3 of the present invention;

[0022] Figure 6 is the PL spectrum of the perovskite nanocrystals prepared in Example 4 of the present invention. Detailed Embodiments

[0023] Example 1:

[0024] In this example, a method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition is as follows:

[0025] (1) Add 0.10 mmol of cesium carbonate and 0.30 mmol of lead bromide into a flask, and then add 10 mL of organic solvent 1-octadecene; then add 1.0 mL of oleic acid and 0.8 mL of oleylamine in sequence to obtain a mixed precursor solution;

[0026] (2) Heat the above mixed precursor solution progressively. The progressive heating regime is to first heat at 80 °C for 20 min, and then raise the temperature to 110 °C and react for 30 min to obtain an initial reaction solution;

[0027] (3) Naturally cool the above initial reaction solution to room temperature. Subsequently, after centrifugation and washing, disperse the obtained precipitate in the organic solvent n-hexane to obtain a CsPbBr3 nanocrystal solution.

[0028] Characterize the product obtained in this example by transmission electron microscopy (TEM). Its morphological characteristics are as Figure 1 shown. It can be seen from the figure that the prepared CsPbBr3 nanocrystals are cubic blocks with a side length of about 10 nm.

[0029] Perform photoluminescence (PL) spectroscopy testing on the product obtained in this example. The test results are as Figure 2 shown. It can be seen from the figure that the center position of the emission peak is 515.8 nm.

[0030] Example 2:

[0031] The difference between the method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition in this example and Example 1 is that:

[0032] In step (2), the progressive heating regime is to first heat at 90 °C for 30 min, and then raise the temperature to 120 °C and react for 30 min.

[0033] Perform photoluminescence (PL) spectroscopy testing on the product obtained in this example. The test results are as Figure 2 shown. An obvious emission peak appears at 516.0 nm for the obtained CsPbBr3 quantum dots, and its fluorescence quantum yield (PLQY) can reach 98.7% (see Figure 3 ).

[0034] Perform X-ray diffraction (XRD) characterization on the product obtained in this example. The results are as Figure 4 shown. It can be seen from the figure that the product of this example is in the CsPbBr3 phase.

[0035] Example 3:

[0036] A method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition in this example is different from Example 1 in that:

[0037] In step (1), the metal salts are 0.14 mmol of cesium carbonate and 0.30 mmol of lead bromide.

[0038] In step (2), the progressive heating regime is that first, it is heated at 90 °C for 30 min, and then the temperature is raised to 100 °C and reacted for 15 min.

[0039] The nanocrystals obtained in step (3) are a mixed phase of Cs4PbBr6 and CsPbBr3.

[0040] The product of this example was characterized by XRD, and the results are as Figure 5 shown. It can be seen from the figure that the product of this example is a mixed phase of Cs4PbBr6 and CsPbBr3.

[0041] Example 4:

[0042] A method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition in this example is different from Example 1 in that:

[0043] In step (1), the metal salts are 0.12 mmol of cesium carbonate and 0.30 mmol of lead bromide; the organic ligands are 1.0 mL of oleic acid and 1.5 mL of octylamine.

[0044] In step (2), the progressive heating regime is that first, it is heated at 90 °C for 30 min, and then the temperature is raised to 130 °C and reacted for 30 min.

[0045] The product obtained in this example was tested by photoluminescence (PL) spectroscopy, and the test results are as Figure 6 shown. An obvious emission peak appeared at 514.6 nm for the obtained sample.

[0046] Example 5:

[0047] A method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition in this example is different from Example 1 in that:

[0048] In step (1), the metal salts are 0.10 mmol of cesium carbonate, 0.15 mmol of lead bromide, and 0.15 mmol of lead iodide; the organic ligands are 1.0 mL of oleic acid and 1.0 mL of oleylamine.

[0049] In step (2), the progressive heating regime is as follows: first, heat at 90 °C for 30 min, and then raise the temperature to 120 °C and react for 30 min.

[0050] The nanocrystals obtained in step (3) are CsPb(Br / I)3.

[0051] Example 6:

[0052] The method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transformation in this example is different from that in Example 1 in that:

[0053] In step (1), the metal salts are 0.10 mmol of cesium carbonate, 0.15 mmol of lead bromide, and 0.15 mmol of lead chloride; the organic ligands are 1.5 mL of oleic acid and 1.5 mL of oleylamine.

[0054] In step (2), the progressive heating regime is as follows: first, heat at 90 °C for 30 min, and then raise the temperature to 130 °C and react for 45 min.

[0055] The nanocrystals obtained in step (3) are CsPb(Br / Cl)3.

[0056] Example 7:

[0057] The method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transformation in this example is different from that in Example 1 in that:

[0058] In step (1), the organic ligands are 1.2 mL of octanoic acid and 1.5 mL of dodecylamine.

[0059] In step (2), the progressive heating regime is as follows: first, heat at 90 °C for 30 min, and then raise the temperature to 120 °C and react for 45 min.

Claims

1. A method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition, characterized in that It includes the following steps: (1) According to the molar ratio n Cs ∶n Pb = 1∶0.2 - 5, cesium carbonate and lead halide are added into a flask, and 1-octadecene, an organic solvent, is added to form a mixed solution with a metal ion concentration of 0.02 - 1.00 mol / L; then, according to the volume ratio of organic acid∶organic amine∶1-octadecene = 0.01 - 0.5∶0.01 - 0.5∶1, the organic acid and the organic amine are added in sequence to obtain a mixed precursor solution; (2) Gradually heat the mixed precursor solution. The progressive heating regime is to first heat at a temperature of 60 - 90 °C for 5 - 120 min, and then raise the temperature to 100 - 150 °C for reaction for 5 - 120 min to obtain an initial reaction solution; (3) Naturally cool the initial reaction solution to room temperature. Subsequently, after centrifugal washing, disperse the obtained precipitate in an organic solvent to obtain an all-inorganic lead halide perovskite nanocrystal solution.

2. The method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition according to claim 1, wherein: The lead halide is one or a combination of lead bromide, lead chloride, and lead iodide.

3. The method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition according to claim 1, characterized in that: The organic acid is butyric acid, octanoic acid, dodecanoic acid, or oleic acid, and the organic amine is butylamine, octylamine, dodecylamine, or oleylamine.

4. The method for synthesizing all-inorganic lead halide perovskite nanocrystals by one-pot in-situ phase transition according to claim 1, characterized in that: In step (3), the organic solvent is n-hexane, toluene, xylene, or dichloromethane.

5. A product prepared by the method for synthesizing all-inorganic lead halide perovskite nanocrystals through one-pot in-situ phase transition according to any one of claims 1 - 4.

6. The product according to claim 5, characterized in that: The phase composition of the perovskite nanocrystals is CsPbX3, or a mixture of CsPbX3 and Cs4PbX6, where X is one or a combination of Cl, Br, and I.

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