Melamine formaldehyde resin coated perovskite quantum dot and preparation method and application thereof

Abstract

The invention belongs to the technical field of perovskite material preparation, and particularly relates to a melamine formaldehyde resin coated perovskite quantum dot and a preparation method and application thereof. The melamine formaldehyde resin coated perovskite quantum dot comprises melamine formaldehyde resin and a perovskite quantum dot, and the melamine formaldehyde resin coats the perovskite quantum dot. The melamine formaldehyde resin (MF) and the perovskite quantum dots in the melamine formaldehyde resin coated perovskite quantum dots are connected through electrostatic force, the perovskite quantum dots are stably packaged in MF polymer spheres, and the MF polymer forms a compact protective layer. The stability of the melamine formaldehyde resin coated perovskite quantum dots is improved, and the problem of failure of the perovskite quantum dots due to exposure in an aging environment is prevented.

Description

Technical Field

[0001] The present invention belongs to the technical field of perovskite material preparation, and particularly relates to a melamine formaldehyde resin-coated perovskite quantum dot, a preparation method thereof and an application thereof. Background Art

[0002] As a semiconductor luminescent material, perovskite quantum dots have excellent optical properties such as high color purity, tunable emission color and high quantum yield. As one of the excellent luminescent conversion layer materials, quantum dots can be excited by blue or ultraviolet LEDs to achieve full-color display of Micro / Mini LEDs, realize RGB emission on a single chip, and finally have a wider color gamut, higher brightness and more vivid colors when applied to Micro / Mini LED displays. The instability of perovskite quantum dots has become the biggest obstacle to their practical applications, and for this reason, a large number of researchers have made great efforts.

[0003] At present, there are many reports on improving the stability of PQDs. For example, Wang et al. stirred the pre-prepared PQDs and mesoporous silica in a non-polar solvent, and after purification, a perovskite quantum dot composite coated with mesoporous silica was obtained. Sun et al. used 3-aminopropyltrimethoxysilane (APTES) as a ligand for quantum dots, and added APTES during the synthesis process to crosslink the quantum dots to obtain a PQDs@SiO2 composite material. Huang et al. used methyl orthosilicate (TMOS) instead of the traditionally used TEOS as a silicon precursor. TMOS can slowly hydrolyze under a certain humidity. The research group mixed MAPbBr3 quantum dots with TMOS in toluene containing a small amount of water, stirred in an open environment with a humidity of 60% for a certain time, and a nano-composite material of PQDs@SiO2 can be obtained after purification. Yang et al. added a certain amount of NaNO3 crystals to the MAPbBr3 precursor solution, and then transferred the precursor solution to toluene. While the quantum dots rapidly precipitate, the NaNO3 crystals will also precipitate simultaneously. Pathak et al. mixed PQs with a toluene solution of PS or polymethyl acrylate (PMMA), and prepared blue, green and red light-emitting films of perovskite quantum dots by centrifugation. Through this structure, the ion exchange between different components of perovskite is effectively blocked, and the application of perovskite in white light LEDs is realized. The composite shows high thermal stability and light stability. However, under harsh aging conditions such as damp heat and strong blue light aging in industrial aging requirements, the above perovskite quantum dot materials cannot maintain stability for a long time. This is because the protection of the quantum dots by the coating material fails during the aging process, which in turn leads to the exposure and failure of the quantum dots, resulting in the failure of the protection of the quantum dots by the coating material during the aging process, and then leading to the exposure and failure of the quantum dots.

[0004] Generally speaking, there are mainly three situations for the reasons of the failure of quantum dots exposed due to the existing coating technologies. (1) During the process of coating perovskite quantum dots or after the coating is completed by the existing coating technologies, the coating layer cannot form stable chemical bonds on the surface of the quantum dots, resulting in the inability to stably preserve the bond chains formed between the coating layer and the quantum dots during the aging process, leading to the failure of the coating structure and further the failure of the quantum dots. (2) The instability of the coating material itself causes the coating material to fail first during the long-term aging process, and then leads to the failure of the quantum dots. (3) The existing coating materials often only form a loose winding structure around the quantum dots and cannot form a dense protective layer. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects that the coating material cannot well protect perovskite quantum dots during the aging process of the existing perovskite coating materials, resulting in the exposure and failure of quantum dots, and the stability of the perovskite coating materials needs to be further improved, etc. Thus, a melamine formaldehyde resin-coated perovskite quantum dot, its preparation method and application are provided.

[0006] For this purpose, the present invention provides the following technical solutions.

[0007] The present invention provides a melamine formaldehyde resin-coated perovskite quantum dot, which includes a melamine formaldehyde resin and a perovskite quantum dot, and the melamine formaldehyde resin coats the perovskite quantum dot.

[0008] The raw materials of the melamine formaldehyde resin-coated perovskite quantum dot include modified perovskite quantum dots.

[0009] The modified perovskite quantum dots have negative charges.

[0010] The raw materials of the modified perovskite quantum dots include at least one of lecithin, amino acid and betaine;

[0011] Preferably, the amino acid is at least one of leucine, isoleucine and phenylalanine.

[0012] The present invention also provides a preparation method of a melamine formaldehyde resin-coated perovskite quantum dot, which includes the following steps:

[0013] (1) Prepare modified perovskite quantum dots;

[0014] (2) Mix the melamine formaldehyde resin prepolymer with the modified perovskite quantum dots and react.

[0015] The step (2) is carried out under airtight conditions;

[0016] Preferably, the reaction time is 2-12 h.

[0017] The perovskite quantum dots in the modified perovskite quantum dots have the structural formula ABX3;

[0018] wherein, A is Cs or FA; B is Pb; X is a halogen;

[0019] Preferably, the molar ratio of B in the mixed solution of melamine and perovskite precursor is (2-6):1. Among them, the raw materials of melamine formaldehyde resin include melamine and formaldehyde.

[0020] The preparation method of the modified perovskite quantum dots includes: adding a solution containing a modifier to the mixed solution of perovskite precursors, and reacting to obtain perovskite quantum dots with negative charges.

[0021] The modifier is at least one of lecithin, amino acid and betaine.

[0022] Furthermore, when preparing the modified perovskite quantum dots, the reaction time is 15 min to 2 h;

[0023] Preferably, when preparing the modified perovskite quantum dots, the solvent in the solution containing the modifier includes at least one of water and an organic solvent;

[0024] Preferably, the organic solvent is an alcohol solvent;

[0025] Preferably, the organic solvent is ethanol and / or methanol;

[0026] Preferably, the molar ratio of B to the modifier in the mixed solution of perovskite precursors is (1-3):(1-2).

[0027] In the present invention, when preparing the melamine formaldehyde resin prepolymer, the reaction temperature can be but is not limited to 50 °C, and the time can be but is not limited to 40 min;

[0028] When preparing the melamine formaldehyde resin, it further includes the step of adding a solvent, and the solvent can be but is not limited to at least one of water, ethanol, methanol, dimethylformamide and dimethyl sulfoxide.

[0029] In addition, the present invention also provides an application of the above-mentioned melamine formaldehyde resin-coated perovskite quantum dots or the melamine formaldehyde resin-coated perovskite quantum dots prepared by the above-mentioned preparation method, and the melamine formaldehyde resin-coated perovskite quantum dots are applied to the fields of lighting, display, laser, detection or solar cells.

[0030] Principle of the melamine formaldehyde resin-coated perovskite quantum dots of the present invention: After synthesizing the perovskite quantum dots, ligands are used for modification to make the surface of the quantum dots negatively charged; the MF prepolymer is positively charged; the halogen ions on the surface of the perovskite quantum dot lattice form a stable structure with one end of the modifier (for example, Br ions form a hydrogen bond stable structure with amino groups, or form a hydrogen bond structure with carboxyl groups, etc.), and the other end makes the surface of the quantum dots negatively charged due to weak ionization; before the MF prepolymer forms polymer microspheres, the perovskite quantum dots are adsorbed on the branched molecules of the MF prepolymer through electrostatic interaction forces, and after the MF prepolymer forms MF polymer microspheres, the quantum dots are encapsulated inside the microspheres, forming a dense coating layer structure.

[0031] The technical solution of the present invention has the following advantages:

[0032] 1. The melamine formaldehyde resin-coated perovskite quantum dots provided by the present invention have excellent optical properties, thermal stability, and resistance to polar solvents and other properties. In the melamine formaldehyde resin-coated perovskite quantum dots of the present invention, the melamine formaldehyde resin (MF) and the perovskite quantum dots are connected by electrostatic interaction forces, and the perovskite quantum dots are stably encapsulated inside the MF polymer microspheres. The MF polymer forms a dense protective layer, improving the stability of the melamine formaldehyde resin-coated perovskite quantum dots and preventing the perovskite quantum dots from failing due to exposure in an aging environment.

[0033] Furthermore, the MF material has a highly cross-linked and porous internal structure, high tolerance to solvents, and good thermal stability, which plays a good protective role for the quantum dots. The MF prepolymer is positively charged and has a branched structure; in the present invention, the surface of the perovskite quantum dots is made negatively charged through modification, forming an electrostatic interaction force with the positive charge in the MF prepolymer, forming a stable chemical bond, firmly adsorbing the perovskite quantum dots inside the branched molecules of the MF prepolymer. The formed melamine formaldehyde resin-coated perovskite quantum dots will neither expose the perovskite quantum dots due to the failure of the coating material during the aging process, nor will the quantum dots be exposed due to the weak force between the coating layer and the quantum dots and the resulting fracture. By forming an electrostatic interaction force between the modified perovskite quantum dots and MF, the present invention can significantly improve the hygrothermal stability of the coated perovskite material.

[0034] 2. For the melamine formaldehyde resin-coated perovskite quantum dots provided by the present invention, lecithin, amino acids, betaine, etc. are introduced onto the surface of the perovskite quantum dots to provide negative charges, which can form electrostatic interaction forces with the melamine formaldehyde resin, improving the thermal stability of the coated perovskite quantum dots.

[0035] 3. The preparation method of the perovskite quantum dots coated with melamine formaldehyde resin provided by the present invention. The melamine formaldehyde resin prepolymer has a positive charge and a branched structure; the modified perovskite quantum dots have a negative charge, and the modified perovskite quantum dots can be combined with the branched small molecules of the melamine formaldehyde resin prepolymer through electrostatic interaction. After the MF prepolymer forms MF polymer microspheres, the modified perovskite quantum dots are stably encapsulated inside the MF microspheres, and the perovskite quantum dots coated with melamine formaldehyde resin are obtained. In the present invention, the perovskite quantum dots are encapsulated inside the MF microspheres, and the MF polymer forms a dense coating layer. A stable chemical bond is formed between the coating layer and the perovskite quantum dots, preventing problems such as quantum dot exposure due to coating layer aging and quantum dot exposure due to bond cleavage between the coating layer and the quantum dots. The perovskite quantum dots coated with melamine formaldehyde resin prepared by the present invention have excellent thermal stability, optical properties and resistance to polar solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0037] Figure 1 It is the potential diagram of the melamine formaldehyde resin prepolymer and the modified perovskite quantum dots provided by each embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following embodiments are provided to better understand the present invention further. They are not limited to the best embodiments, and do not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0039] For those steps or conditions not specified in the examples, the operations or conditions of the conventional experimental steps described in the literature in the art can be followed. For the reagents or instruments not specified by the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0040] In some specific embodiments, a preparation method of perovskite quantum dots coated with melamine formaldehyde resin is provided, including the following steps:

[0041] (1) Prepare a perovskite precursor mixed solution; specifically, the structural formula of the perovskite quantum dots is ABX3, where the A-site element is Cs, FA provided by cesium carbonate, formamidinium acetate, etc., the B-site element is Pb provided by lead oxide, and X is a halogen element provided by dilute hydrochloric acid, hydroiodic acid, and hydrobromic acid; first prepare a solution containing A, a solution containing B, and a solution containing X, and mix them to obtain a perovskite precursor mixed solution.

[0042] After the color of the perovskite precursor mixed solution turns milky white, add a solution containing a modifier and react to obtain modified perovskite quantum dots, that is, perovskite quantum dots with negative charges.

[0043] (2) Mix melamine and paraformaldehyde to obtain a transparent melamine formaldehyde resin prepolymer solution; mix it with the modified perovskite quantum dot solution and react to obtain melamine formaldehyde resin-coated perovskite quantum dots, that is, perovskite quantum dots coated with melamine formaldehyde microspheres.

[0044] Example 1

[0045] This example provides a preparation method for melamine formaldehyde resin-coated perovskite quantum dots, including the following steps:

[0046] (1) Take 0.325 g of cesium carbonate, 2 ml of oleic acid and 20 ml of 1-octadecene solvent, mix and stir, slowly heat to 110 °C and keep under vacuum for 30 min, then cool to room temperature to obtain precursor solution -1.

[0047] Take 0.446 g of lead oxide, 2 ml of oleic acid and 20 ml of 1-octadecene, mix and stir, slowly heat to 120 °C and keep under vacuum for 30 min, then cool to room temperature to obtain precursor solution -2.

[0048] Take 1.2 ml of 48 wt% hydrobromic acid and 10 ml of oleylamine, mix and stir, slowly heat to 110 °C and keep under vacuum for 30 min, then cool to room temperature to obtain precursor solution -3.

[0049] Take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of the precursor solutions 1-3. After the solution color turns milky white, add 1 ml of methanol and 1 ml of a betaine aqueous solution (the concentration of betaine is 0.03 mmol / ml), and stir for 30 min to obtain a betaine-modified perovskite quantum dot solution.

[0050] (2) Take 2.6 g of melamine, 3.7 g of paraformaldehyde and 50 mL of water, mix and heat to 50 °C, then stir magnetically for 40 min, and filter to obtain a transparent MF prepolymer solution.

[0051] (3) Mix 5 ml of the betaine-modified perovskite quantum dot solution and 1 ml of the MF prepolymer solution, and stir for 24 h under closed conditions to obtain perovskite quantum dots coated with melamine formaldehyde resin.

[0052] Example 2

[0053] This example provides a method for preparing perovskite quantum dots coated with melamine formaldehyde resin, which includes the following steps:

[0054] (1) Prepare precursor solutions 1-3 according to Example 1 for standby; Take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of precursor solutions 1-3. After the solution color turns milky white, add 1 ml of methanol and 1 ml of a lecithin aqueous solution (the concentration of lecithin is 0.03 mmol / ml), and stir for 30 min to obtain a lecithin-modified perovskite quantum dot solution.

[0055] (2) Prepare the MF prepolymer solution according to Example 1.

[0056] (3) Mix 5 ml of the lecithin-modified perovskite quantum dot solution and 1 ml of the MF prepolymer solution, and stir for 24 h under closed conditions to obtain perovskite quantum dots coated with melamine formaldehyde resin.

[0057] Example 3

[0058] This example provides a method for preparing perovskite quantum dots coated with melamine formaldehyde resin, which includes the following steps:

[0059] (1) Prepare precursor solutions 1-3 according to Example 1 for standby; Take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of precursor solutions 1-3. After the solution color turns milky white, add 1 ml of methanol and 1 ml of a leucine aqueous solution (the concentration of leucine is 0.03 mmol / ml), and stir for 40 min to obtain a leucine-modified perovskite quantum dot solution.

[0060] (2) Prepare the MF prepolymer solution according to Example 1.

[0061] (3) Mix 5 ml of the leucine-modified perovskite quantum dot solution and 1 ml of the MF prepolymer solution, and stir for 24 h under closed conditions to obtain perovskite quantum dots coated with melamine formaldehyde resin.

[0062] Example 4

[0063] This example provides a method for preparing perovskite quantum dots coated with melamine formaldehyde resin, which includes the following steps:

[0064] (1) Prepare the precursor solution 1-3 according to Example 1 for standby; take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of the precursor solutions 1-3. After the solution color turns milky white, add 1 ml of methanol and 1 ml of phenylalanine aqueous solution (the concentration of phenylalanine is 0.03 mmol / ml), and stir for 60 min to obtain a phenylalanine-modified perovskite quantum dot solution.

[0065] (2) Prepare the MF prepolymer solution according to Example 1.

[0066] (3) Mix 5 ml of the phenylalanine-modified perovskite quantum dot solution and 1 ml of the MF prepolymer solution, and stir for 24 h under closed conditions to obtain perovskite quantum dots coated with melamine formaldehyde resin.

[0067] Comparative Example 1

[0068] This comparative example provides a method for preparing perovskite quantum dots. Prepare the precursors 1-3 according to the example. Take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of the precursor solutions 1-3, and stir to obtain a perovskite quantum dot dispersion.

[0069] Comparative Example 2

[0070] This comparative example provides a method for preparing coated perovskite quantum dots. The difference from Example 1 is that water and ethanol solvents are directly added during the quantum dot synthesis process without modifying the surface of the quantum dots. The specific steps are as follows:

[0071] (1) Prepare the precursor solution 1-3 according to Example 1 for standby; take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of the precursor solutions 1-3, and stir for 30 min to obtain a perovskite quantum dot solution.

[0072] (2) Prepare the MF prepolymer solution according to Example 1.

[0073] (3) Mix 5 ml of the perovskite quantum dot solution and 1 ml of the MF prepolymer solution, and stir for 24 h under closed conditions to obtain perovskite quantum dots coated with melamine formaldehyde resin.

[0074] Comparative Example 3

[0075] This comparative example provides a method for preparing coated perovskite quantum dots, including:

[0076] (1) Prepare the precursor solution 1-3 according to Example 1. Take 10 ml of toluene in a beaker, stir, and sequentially add 1 ml of each of the precursor solutions 1-3, and stir for 15 min to 2 h to obtain a perovskite quantum dot solution.

[0077] (2) Add 0.01 g of mesoporous SiO2 (pore size 2 - 50 nm) to 5 ml of perovskite quantum dot solution, and stir for 24 h under airtight conditions to obtain silica-coated perovskite quantum dots.

[0078] Test Example

[0079] This test example provides the performance test results of the perovskite quantum dot products in the examples and comparative examples, which are as follows:

[0080] Prepare films from the perovskite quantum dot products provided in each example and comparative example, and test their damp heat stability; among them, the film preparation process includes: dissolving PS particles in toluene to form a mixed solution, then adding the perovskite quantum dot product to the mixed solution, and forming a film after the solvent evaporates; the test conditions for damp heat stability are an environment of 65 °C and 95% humidity, monitor the change in PLQY in the aging environment, and test the time maintained when the PLQY decreases by 20% (T80) in this environment, that is, the evaluation criterion for the damp heat stability of the coated perovskite quantum dots. The results are shown in Table 1.

[0081] Table 1 Performance test results of the coated perovskite quantum dots in the examples and comparative examples

[0082] Example 6595 / T80 Time Example 1 133h Example 2 125h Example 3 144h Example 4 136h Comparative Example 1 0.5h Comparative Example 2 58h Comparative Example 3 16h

[0083] Compared with the existing coating materials such as APTES, TMOS, SiO2, ZIF, COF, PMMA, and PS, using MF as the coating material in the present invention can significantly improve the damp heat stability of the coated perovskite quantum dots. From the above results, it can be seen that the melamine formaldehyde resin-coated perovskite quantum dots provided by the present invention have good damp heat stability.

[0084] Figure 1 is the potential diagram of the melamine formaldehyde resin prepolymer and the modified perovskite quantum dots provided in each example. From Figure 1 it can be seen that the melamine formaldehyde resin prepolymer prepared in Example 1 has a positive charge, and the modified perovskite quantum dots prepared in Examples 1 - 4 have a negative charge, indicating that there is an electrostatic interaction between the melamine formaldehyde resin and the modified perovskite quantum dots.

[0085] Obviously, the above examples are only for clear illustration and not a limitation of the implementation manner. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A melamine formaldehyde resin-coated perovskite quantum dot, characterized in that, It includes melamine formaldehyde resin and perovskite quantum dots, and the melamine formaldehyde resin coats the perovskite quantum dots.

2. The perovskite quantum dots coated with melamine formaldehyde resin according to claim 1, wherein Its raw materials include modified perovskite quantum dots.

3. The perovskite quantum dots coated with melamine formaldehyde resin according to claim 2, wherein, The modified perovskite quantum dots have negative charges.

4. The perovskite quantum dot coated with melamine formaldehyde resin according to claim 2 or 3, characterized in that, The raw materials of the modified perovskite quantum dots include at least one of lecithin, amino acids and betaine; Preferably, the amino acids are at least one of leucine, isoleucine and phenylalanine.

5. A preparation method of perovskite quantum dots coated with melamine formaldehyde resin, characterized in that, It includes the following steps: (1) Prepare modified perovskite quantum dots; (2) Mix the melamine formaldehyde resin prepolymer with the modified perovskite quantum dots and react.

6. The preparation method according to claim 5, characterized in that, The step (2) is carried out under airtight conditions; Preferably, the reaction time is 2 - 12 h.

7. The preparation method according to claim 5 or 6, characterized in that, The perovskite quantum dots in the modified perovskite quantum dots have the structural formula ABX3; Among them, A is Cs or FA; B is Pb; X is a halogen; Preferably, the molar ratio of B in the mixed solution of melamine and perovskite precursor is (2 - 6):

1.

8. The preparation method according to any one of claims 5-7, characterized in that, The preparation method of the modified perovskite quantum dots includes: adding a solution containing a modifier to the perovskite precursor mixed solution, reacting to obtain perovskite quantum dots with negative charges.

9. The preparation method according to any one of claims 5-8, characterized in that, When preparing the modified perovskite quantum dots, the reaction time is 15 min to 2 h; Preferably, when preparing the modified perovskite quantum dots, the solvent in the solution containing the modifier includes at least one of water and organic solvents; Preferably, the organic solvent is an alcohol solvent; Preferably, the organic solvent is ethanol and / or methanol; Preferably, the molar ratio of B and the modifier in the perovskite precursor mixed solution is (1 - 3):(1 - 2).

10. Use of the melamine formaldehyde resin-coated perovskite quantum dots according to any one of claims 1-4 or the melamine formaldehyde resin-coated perovskite quantum dots prepared by the preparation method according to any one of claims 5-9, characterized in that, The melamine formaldehyde resin-coated perovskite quantum dots are applied to the fields of lighting, display, laser, detection or solar cells.

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