An aqueous solution of metal halide, a perovskite phosphor and a preparation method thereof

Abstract

The present invention discloses an aqueous solution of a metal halide precursor and a perovskite phosphor prepared therefrom and a preparation method thereof. The aqueous precursor solution is composed of water, AX, APb2X5, and CsX, wherein A = K, Na, and X = Cl, Br. Through the way of drying and crystallization, a perovskite phosphor composed of AX, APb2X5, CsPb2X5, and CsPbX3 nanocrystals can be obtained, and the APb2X5, APb2X5, CsPb2X5, and CsPbX3 nanocrystals are coated inside the AX crystal. The aqueous solution described in the present invention can be combined with water-soluble resins, etc. to form printing inks, made into films, etc. for use. The perovskite phosphor described can be mixed with various adhesives for use, and the usage methods are diverse; the preparation process adopted has the characteristics of low manufacturing cost, easy operation, short cycle, and environmental friendliness.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronic materials, and particularly relates to a perovskite phosphor and a preparation method thereof. Background Art

[0002] Phosphors are an important class of luminescent materials and are widely used in fields such as displays and lighting. However, the current phosphor materials have broad emission peaks, resulting in low color rendering coefficients and narrow color gamuts, making it difficult to meet the requirements of high color purity and high-resolution display applications. Compared with traditional phosphor powders, metal halide perovskite luminescent materials have attracted extensive attention in the optoelectronic field due to their narrow spectra (15 - 25 nm), high defect tolerance, and bright color emissions.

[0003] Existing preparation techniques for metal halide perovskite luminescent materials mainly include the hot injection method, saturated recrystallization method, etc. However, the synthesis of phosphor materials prepared by the hot injection method requires the protection of inert gas and inevitably high-temperature reactions during the process, making it difficult to achieve large-scale production expansion (Nano Lett., 2015, 15, 6, 3692); in addition, the solvents used in the saturated recrystallization method are N,N-dimethylformamide diethyl acetal, DMSO, DMF, and γ-butyrolactone. These solvents are toxic and environmentally unfriendly. For example, N,N-dimethylformamide diethyl acetal can cause damage to human skin (Adv. Funct. Mater., 2016, 26, 2435); moreover, the perovskite luminescent materials prepared by the above methods are all in a colloidal state and are difficult to be stored in the form of powder like phosphor materials. Most of them are stored in expensive and environmentally unfriendly organic solvents, otherwise their optical properties will deteriorate, hindering their development in practical applications.

[0004] To solve the above problems, replacing the previous solvent with a less toxic solvent is a better solution. For example, alcohol solvents (ACS Nano, 2019, 13, 8237) can be used to achieve the original purpose of reducing harm. In addition, water, as a green and environmentally friendly solvent, is also attractive for synthesizing metal halide perovskite materials. However, the difficulty with using water as a solvent is that lead precursors are difficult to dissolve in aqueous solutions, so it is difficult to obtain fluorescent materials with high luminescence performance. Using sodium docusate as a ligand, nanocrystals with high luminescence performance can be obtained with water as a solvent. Unfortunately, this method requires a condition of -196 °C for preparation, which greatly increases its production cost (Nanoscale, 2020, 12, 6522). By controlling the pH in the range of 0 - 5 and using an aqueous hydrobromic acid solution as a solvent, researchers can prepare luminescent perovskite materials (Angew. Chem. Int. Ed., 2018, 57, 9650); Chinese invention patent CN106833634A reports the preparation of organic-inorganic hybrid lead halides using water as a solvent to replace traditional organic solvents. However, the luminescence performance of these products is very low, with a quantum yield of only 40%. In addition, the prepared materials are colloids and all need to be stored in harsh environments, such as airtight conditions and encapsulation, which makes the cost much higher than traditional phosphors and is difficult to meet practical applications. Summary of the Invention

[0005] In view of the problems of the prior art, the present invention provides an aqueous solution of metal halide, a perovskite phosphor prepared therefrom, and a preparation method thereof. The aqueous solution of metal halide is composed of 100 parts by mass of water, 9.3 - 25.2 parts of AX, 0.53 - 48.8 parts of APb2X5, and 1.4 - 22.6 parts of CsX. The perovskite phosphor prepared from this aqueous solution is composed of AX with a mass percentage content of 20.5 - 96%, 0 - 40% of APb2X5, 0 - 35% of CsPb2X5, and 1.8 - 30% of CsPbX3 nanocrystals. Moreover, the APb2X5, CsPb2X5, and CsPbX3 perovskite nanocrystals are coated inside the AX crystals. In the aqueous solution of metal halide and the perovskite phosphor: A = K, Na, X = Cl, Br. The preparation method is to mix the precursor materials for preparing the metal halide phosphor with an aqueous solution to obtain an aqueous solution of metal halide, and then the perovskite phosphor is synthesized by evaporation crystallization of this solution. The synthesized perovskite phosphor is a solid powder of perovskite nanocrystals tightly coated with a halide matrix.

[0006] The preparation method includes the following steps:

[0007] (1) Dissolve AX in water to obtain an aqueous solution of AX;

[0008] (2) Dissolve PbX2 in the aqueous solution of AX to obtain a mixed aqueous solution of AX and APb2X5;

[0009] (3) Add the aqueous solution of CsX to the above-mentioned mixed aqueous solution;

[0010] (4) Filter the precipitate to obtain a clear aqueous solution, which is the aqueous solution of the metal halide;

[0011] (5) Dry the aqueous solution of the metal halide to obtain the phosphor.

[0012] The aqueous solution of the metal halide and the perovskite phosphor involve the following reaction process:

[0013] (I) AX + PbX2 → APb2X5

[0014] (II) APb2X5 + CsX ←→ CsPb2X5 + AX

[0015] (III) CsPb2X5 + CsX ←→ 2CsPbX3

[0016] During the reaction process, the ratio and concentration of the reactants will affect the resulting products. For example, in step (1) of the preparation method, the concentration of AX is 0.1 - 4.25 mol / L. If it is lower than 0.1 mol / L, it is easy to cause the aggregation of the perovskite fluorescent material in the product to form a bulk material, resulting in a significant reduction in the fluorescence intensity emitted by the product. If the concentration is too high, it will exceed the solubility of the AX solution, resulting in an increase in by-products and affecting the product yield.

[0017] In step 2, when PbX2 is dissolved in the precursor halide aqueous solution of step 1, the molar ratio of PbX2 to AX is 1:2 - 1:100. When it is lower than 1:100, less of the claimed perovskite fluorescent material is produced and the product emits weak light; when it is higher than 1:2, the reactants are not easily dissolved, which easily causes a reduction in the yield, and the prepared material contains more impurity phases and the product agglomerates, thereby affecting the luminescence efficiency. In the aqueous solution, the perovskite precursor material exists in an ionic state, making the crystallization process more balanced. Otherwise, the product will be impure and have impurity phases.

[0018] In step 3, the concentration of the added aqueous solution of CsX is 0.008 - 0.85 mol / L. If the concentration is too high, it is easy to produce impurity phases with weak luminescence and it is easy to wrap the perovskite phase with strong luminescence; if the concentration is too low, the luminescence intensity of the phosphor is low.

[0019] In the aqueous solution of CsX added in step 3, the molar ratio of CsX to PbX2 in the second step is 1:1 - 1:2.5. If the ratio is inappropriate, the perovskite nanocrystals cannot be crystallized out or the concentration is too high, resulting in the aggregation of the nanocrystals, causing a sharp reduction in their luminescence performance.

[0020] The perovskite nanocrystals obtained in Step 4 are in single-particle dispersion, with an average particle size of 5 - 15 nm. As a further preference of the present invention, the metal halide perovskite solid powder tightly coated with a halide matrix is obtained by evaporation crystallization of a precursor solution, and the perovskite nanocrystals grow by heterogeneous nucleation inside the halide matrix.

[0021] Compared with the prior art, the technical solution of the present invention can achieve the following beneficial effects:

[0022] (1) In terms of process, the synthesis method of the present invention does not require high-temperature heating; using an aqueous solution as a solvent, as long as the raw materials are simply mixed, dissolved, shaken, and recrystallized, water is used to replace toxic organic solvents, reducing the health risks of production personnel and alleviating environmental pollution. The conditions required for synthesis and the professional technical requirements of experimental operators are greatly reduced; only water participates in this reaction, so the requirement for the water content in the environment is not high; (2) The phosphor synthesized by the present invention has excellent luminescence properties, with a half-width of only 21 nm and a quantum yield of over 80%, providing a new method for subsequent device development and having high application value; (3) Water-based resins and water-based emulsions can be added to the obtained metal halide aqueous solution to prepare luminescent films, greatly broadening its application scope; (4) The prepared perovskite phosphor has excellent stability because the perovskite nanocrystals are coated with a dense halide. Description of the Drawings

[0023] Appendix Figure 1 : Scanning electron microscope and transmission electron microscope pictures of the phosphor in Example 1;

[0024] Appendix Figure 2 : Absorption and emission spectra of the phosphor in Example 1, and the inset is a photo of it under irradiation by a 365 nm ultraviolet lamp;

[0025] Appendix Figure 3 : XRD pattern of the phosphor in Example 1;

[0026] Appendix Figure 4 : Luminescent film obtained in Example 5;

[0027] Appendix Figure 5 : Metal halide aqueous solution obtained in Example 5;

[0028] Appendix Figure 6 : Relationship diagram between the luminescence intensity of the phosphor in Example 1 and the storage time in air. Specific Embodiments

[0029] Example 1

[0030] Dissolve 43 g of potassium bromide in 100 mL of aqueous solution at room temperature to form an aqueous potassium bromide solution (the corresponding metal halide can be completely dissolved by shaking or stirring at room temperature). Add 3.67 g of lead bromide to the above solution and stir well to obtain a mixed aqueous solution of KBr and KPb2Br5. Then add 2.2 g of cesium bromide to the above mixed aqueous solution and stir well to obtain an aqueous metal halide solution. Dry the aqueous metal halide solution in an oven at 80 °C to obtain green-emitting perovskite phosphor.

[0031] Example 2

[0032] Dissolve 53.5 g of sodium bromide in 100 mL of aqueous solution at room temperature to form an aqueous sodium bromide solution (the corresponding metal halide can be completely dissolved by shaking or stirring at room temperature). Add 3.67 g of lead bromide to the above solution and stir well to obtain a mixed aqueous solution of NaBr and NaPb2Br5. Then add 5.5 g of cesium bromide to the above mixed aqueous solution and stir well to obtain an aqueous metal halide solution. Dry the aqueous metal halide solution in an oven at 100 °C to obtain green-emitting perovskite phosphor.

[0033] Example 3

[0034] Dissolve 28.7 g of sodium chloride in 100 mL of aqueous solution at room temperature to form an aqueous sodium chloride solution (the corresponding metal halide can be completely dissolved by shaking or stirring at room temperature). Add 2.78 g of lead chloride to the above solution and stir well to obtain a mixed aqueous solution of NaCl and NaPb2Cl5. Then add 2.2 g of cesium bromide to the above mixed aqueous solution and stir well. Take the supernatant to obtain an aqueous metal halide solution. Dry the aqueous metal halide solution in an oven at 80 °C to obtain blue-emitting phosphor.

[0035] Example 4

[0036] Dissolve 43 g of potassium bromide in 100 mL of aqueous solution at room temperature to form an aqueous potassium bromide solution (the corresponding metal halide can be completely dissolved by shaking or stirring at room temperature). Add 2.78 g of lead chloride to the above solution and stir well to obtain a mixed aqueous solution of KBr and KPb2(Br,Cl)5. Then add 2.2 g of cesium bromide to the above mixed aqueous solution and stir well to obtain an aqueous metal halide solution. Dry the aqueous metal halide solution at 80 °C to obtain blue-green-emitting perovskite phosphor.

[0037] Example 5

[0038] Dissolve 43 g of potassium bromide in 100 mL of aqueous solution at room temperature to form an aqueous potassium bromide solution. Add 3.67 g of lead bromide to the above solution and stir well to obtain a mixed aqueous solution of KBr and KPb2Br5. Then add 2.2 g of cesium bromide to the above mixed aqueous solution and stir well. Take the supernatant to obtain an aqueous metal halide solution. Add polyvinylpyrrolidone with a mass fraction of 10 wt% to this aqueous solution to finally obtain a metal halide perovskite precursor solution. A water-based film can be prepared by coating the film.

[0039] Control example:

[0040] Dissolve 3 g of potassium bromide in 100 mL of aqueous solution at room temperature to form an aqueous potassium bromide solution. Add 3.67 g of lead bromide to the above solution and stir well. Then add 2.2 g of cesium bromide to the above mixed aqueous solution and stir well to obtain an aqueous metal halide solution. Dry the aqueous metal halide solution in an oven at 80 °C, and the obtained product has no fluorescence effect.

Claims

1. A method for preparing a perovskite phosphor, characterized in that, It includes the following steps: (1) Dissolve AX in water to obtain an aqueous solution of AX; (2) Add PbX2 to the aqueous solution of AX and dissolve it to obtain a mixed aqueous solution of AX and APb2X5; (3) Add an aqueous solution of CsX to the above-mentioned mixed aqueous solution; (4) Filter the precipitate to obtain an aqueous solution of metal halide; (5) Dry the aqueous solution of the metal halide to obtain the phosphor; The perovskite phosphor is composed of AX with a mass percentage of 20.5 - 96%, 0 - 40 wt% of APb2X5, 0 - 35% of CsPb2X5, and 1.8 - 30% of CsPbX3 nanocrystals, and the APb2X5, CsPb2X5, and CsPbX3 nanocrystals are coated inside the AX crystal; The aqueous solution of the metal halide is composed of 100 parts by mass of water, 9.3 - 25.2 parts of AX, 0.53 - 48.8 parts of APb2X5, and 1.4 - 22.6 parts of CsX; A = K, Na; X = Cl, Br; The concentration of the aqueous solution of AX in step (1) is 0.1 - 4.25 mol / L; The molar ratio of PbX2 to AX in step (2) is 1:2 - 1:100; In step (3), the molar ratio of CsX in the added aqueous solution of CsX to PbX2 in step (2) is 1:1 - 1:2.

5.

2. The preparation method of the perovskite phosphor according to claim 1, characterized in that, The concentration of the aqueous solution of CsX in step (3) is 0.008 - 0.85 mol / L.

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