Silicone ligands for stabilizing quantum dots, silicone-modified quantum dots, and methods of making the same

Abstract

The present application relates to a kind of organic silicon ligand for stabilizing quantum dot, organic silicon modified quantum dot and its preparation method, the ligand provided by the present application is a kind of organic silicon molecule that can replace oil amine oil acid as quantum dot ligand, for encapsulating quantum dot, effectively improve the anti-light and thermal stability and processing performance of quantum dot. By solution casting method, quantum dot fluorescent film is prepared, and finally successfully obtain high stability, high fluorescent efficiency and high transmittance of organic silicon encapsulated quantum dot fluorescent film with low cost compared with the current widely used system of introducing exogenous matrix (polystyrene) encapsulating quantum dot, the organic silicon encapsulated quantum dot film of the present application shows better anti-ultraviolet and thermal stability, higher fluorescent efficiency, better transmittance in scattering area and lower film making cost. The present application successfully realizes low-cost high-performance quantum dot fluorescent film, which will promote the practical application of quantum dot film in the field of light emitting and display.

Description

TECHNICAL FIELD

[0001] The present application relates to organosilicon ligands for stabilizing quantum dots, organosilicon-modified quantum dots and methods for their preparation, and belongs to the field of inorganic nanophosphors. BACKGROUND

[0002] Inorganic semiconductor quantum dots (including chalcogenides, sulfides and halide perovskites) have attracted great attention from both academia and industry due to their excellent optical properties (high fluorescence quantum yield > 90%, narrow full width at half maximum ≈ 12-40 nm, tunable emission peak wavelength ≈ 400-700 nm) and mature and inexpensive synthesis strategies [Laser Photon. Rev. 2022, 220055.]. Some well-known semiconductor display companies have launched display products based on quantum dots as light conversion media, which is a powerful signal for the commercialization of quantum dot light-emitting materials [Nat. Rev. Mater. 2022, 7(10), 757-777.]. However, in current practical applications, compared to traditional rare earth element-doped luminescent materials, the intrinsic stability of quantum dots, especially halide perovskite materials, is poor and their optical properties are easily affected by environmental factors such as water and oxygen, which has become a bottleneck for their further commercialization. Therefore, it is of great industrial value to research and develop efficient strategies for stabilizing quantum dots. Encapsulation based on inorganic oxides and organic polymers can provide effective physical isolation for quantum dot materials to prevent them from being affected by environmental factors such as water and oxygen, thereby significantly improving their resistance to light, heat and chemical stability [Adv. Mater. 2022, e2209784.]. However, both polymer and inorganic oxide encapsulation are difficult to balance the good light and heat resistance of quantum dots and still maintain the excellent solution processing performance of quantum dots.

[0003] The encapsulation strategy of organosilica can make up for the shortcomings of inorganic oxide and organic polymer encapsulation strategies and integrate their advantages, effectively improve the photostability and thermal stability of quantum dots, and well maintain the solution processability of quantum dots. It is a very promising quantum dot encapsulation strategy [Adv. Opt. Mater. 2020, 8(17), 2000501.]. Compared with the encapsulation strategy of polymers, organosilica can provide better photostability and thermal stability for quantum dot materials due to the presence of a large number of inorganic O-Si-O bonds in the system. Secondly, compared with the encapsulation strategy of inorganic oxides, organosilica can be cross-linked into a film through the condensation of silicate bonds, so that the precursor has film-forming and solution processing properties similar to polymer materials. Although it has certain advantages, inert long carbon chain ligands (such as oleic acid) are widely used in the current organosilica encapsulated quantum dot system to stabilize colloidal quantum dots [Angew. Chem.-Int. Edit. 2016, 55(31), 8864-8868.]. Although the long carbon chain ligand molecules play an important role in preparing high-fluorescent colloidal quantum dots (including: preparing precursors, assisting quantum dot nucleation and growth, providing colloidal stability and passivating quantum dot surface defects), their inertness and steric hindrance hinder the further improvement of the performance of organosilica encapsulated quantum dot films, resulting in the current performance deficiencies of organosilica encapsulated quantum dot films (such as low transparency, large surface roughness, low fluorescence efficiency, and insufficient adhesion, etc.).

[0004] Chinese patent document CN111057536A discloses a kind of silicon-based ligand modified all-inorganic perovskite quantum dot composite polydimethylsiloxane fluorescent film;The perovskite quantum dot is CsPbX3, wherein X is one of Cl, Br, I;The size of CsPbX3 quantum dot is about 2-50nm. The film utilizes the good compatibility of polydimethylsiloxane and silicon-based ligand, can effectively coat CsPbX3 quantum dot, realizes high-stability flexible fluorescent film and its preparation method, improves the thermal stability of perovskite quantum dots, so that quantum dots do not occur agglomeration in high temperature curing process, and ensure that quantum dots can be uniformly dispersed in polydimethylsiloxane. However, the patent introduces an exogenous encapsulation matrix in the preparation process, which significantly reduces the solid content of fluorescent quantum dots in the quantum dot film. In addition, it is difficult to prepare thinner films (<500nm). Secondly, the ligand is not enough to passivate the surface defects of quantum dots, so that the prepared quantum dot film has low fluorescence efficiency.

[0005] Therefore, there is an urgent need to develop a quantum dot film with high transparency, high fluorescence efficiency and low surface roughness. SUMMARY

[0006] In view of the problems of the existing organic silicon encapsulated quantum dots, especially the problems of low transparency, low fluorescence efficiency and high surface roughness, the present application aims to provide an organic silicon ligand for stabilizing quantum dots, an organic silicon modified quantum dot and a preparation method thereof.

[0007] The ligand provided by the present application is a kind of organic silicon molecule capable of replacing oleylamine and oleic acid as a quantum dot ligand, and is used for encapsulating quantum dots to effectively improve the light and heat stability and processing performance of the quantum dots.

[0008] The present application prepares a quantum dot fluorescent film by a solution casting method, and finally successfully obtains an organic silicon encapsulated quantum dot fluorescent film with high stability, high fluorescence efficiency and high light transmittance at low cost, the obtained quantum dot film has high fluorescence quantum efficiency (more than 90%), high light transmittance (more than 90% in a scattering area under a film thickness of 40 microns) and low surface roughness (less than 30 nm under a film thickness of 40 microns), and has good potential for application in the fields of display and X-ray imaging.

[0009] The present application is realized by the following technical scheme:

[0010] The first object of the present application provides an organic silicon ligand molecule for stabilizing quantum dots.

[0011] The organic silicon ligand for the surface of the quantum dot includes an organic silicon ligand A and an organic silicon ligand B, the organic silicon ligand A is a kind of silane coupling agent with amino as a terminal, is an analogue of gamma-aminopropyl triethoxysilane, and the general structure thereof is NH2-R1-Si(OR2)3, wherein R1 is an alkylene group with a C atom number of more than or equal to 3, and plays a role of coupling amino and silicate functional groups, and R2 is methyl, ethyl or propyl.

[0012] The organic silicon ligand B is a kind of silane coupling agent with carboxyl as a terminal, the general structure thereof is HOOC-R3-Si(OR2)3, wherein R3 is selected from a carbon chain with a C atom number of more than or equal to 10, or a carbon chain containing a carbonyl, an amide bond, an ester bond or an ether bond with a C atom number of more than or equal to 10, and plays a role of coupling carboxyl and silicate functional groups; and R2 is methyl, ethyl or propyl.

[0013] According to the present application, the organic silicon ligand A contains a trialkoxy silane tail, an amino group, a double amino group or a triple amino group head, and specifically, the organic silicon ligand A has the structures shown in A1, A2 or A3 as follows:

[0014]

[0015] According to the present application, the organic silicon ligand B contains a carboxyl head and a trialkoxy silane tail, and has the structures shown in B1, B2, B3 or B4 as follows:

[0016]

[0017] According to the present application, the trialkoxysilane tail mentioned above can be trialkylethoxysilane, trialkylmethoxysilane, trialkyl-t-butoxysilane, as long as the purpose of the present application can be achieved.

[0018] According to the present application, the preferred organosilicon ligand A1, A2, A3 are commercially available products, and the trade names of A1, A2 and A3 are γ-aminopropyltrimethoxysilane, N-aminoethyl-3-aminopropylmethyldimethoxysilane and γ-divinyltriaminepropylmethyldimethoxysilane coupling agent, respectively.

[0019] According to the present application, the preferred organosilicon ligand B1, B2, B3 and B4 are prepared by the following method:

[0020] The organosilicon ligand B1 is prepared by the following method: 0.68g of adipic anhydride and 1.17g of A1 molecules are dissolved in 10mL of tetrahydrofuran, and then refluxed at 60℃ for 12h, the product is collected and the residual solvent is removed by rotary evaporation.

[0021] The organosilicon ligand B2 is prepared by the following method: 0.59g of glutaric anhydride and 1.17g of A1 molecules are dissolved in 10mL of tetrahydrofuran, and then refluxed at 60℃ for 12h, the product is collected and the residual solvent is removed by rotary evaporation.

[0022] The organosilicon ligand B3 is prepared by the following method: 0.76g of 2,2-dimethylglutaric anhydride and 1.17g of A1 molecules are dissolved in 10mL of tetrahydrofuran, and then refluxed at 60℃ for 12h, the product is collected and the residual solvent is removed by rotary evaporation.

[0023] The organosilicon ligand B4 is prepared by the following method: 0.61g of diglycolic anhydride and 1.17g of A1 molecules are dissolved in 10mL of tetrahydrofuran, and then refluxed at 60℃ for 16h, the product is collected and the residual solvent is removed by rotary evaporation.

[0024] The second object of the present application is to provide a preparation method of a full organosilicon ligand modified colloidal quantum dot.

[0025] A preparation method of a full organosilicon ligand modified colloidal quantum dot, comprising the following steps:

[0026] 1) Mix cesium bromide, lead bromide and N,N-dimethylformamide, and ultrasonically disperse until completely dissolved to obtain a mixed solution;

[0027] 2) Add organosilicon ligand A and organosilicon ligand B to the mixed solution, continue stirring until completely dissolved to obtain a quantum dot precursor;

[0028] 3) The quantum dot precursor is injected into the strongly stirred toluene at room temperature to obtain the organosilicon ligand modified colloidal quantum dots.

[0029] According to the application, preferably, in step 1), the mass ratio of cesium bromide and lead bromide is (0.03-0.05):(0.06-0.08), and the mass-volume ratio of cesium bromide and N,N-dimethylformamide is (0.03-0.05):(4-10) g / mL.

[0030] According to the application, preferably, in step 2), the mass ratio of organosilicon ligand A and organosilicon ligand B is (100-120):(130-150).

[0031] According to the application, preferably, in step 2), the mass-volume ratio of organosilicon ligand A and N,N-dimethylformamide is (100-120):(4-10) mg / mL.

[0032] According to the application, preferably, in step 3), the volume ratio of quantum dot precursor and toluene is (0.4-0.8):(5-15).

[0033] The third object of the application is to provide a preparation method of organosilicon ligand modified colloidal quantum dot fluorescent film.

[0034] The preparation method of organosilicon ligand modified colloidal quantum dot fluorescent film comprises the following steps:

[0035] (1) The organosilicon ligand modified colloidal quantum dot solution is dropped on a clean glass slide,

[0036] (2) The glass slide is transferred to a drying oven for heating, so that the solvent is volatilized and the organosilicon is fully condensed and crosslinked to form a film, and finally the organosilicon ligand modified colloidal quantum dot fluorescent film is prepared.

[0037] According to the application, preferably, in step (1), the amount of organosilicon ligand modified colloidal quantum dot solution is 0.1-0.5 mL.

[0038] According to the application, preferably, in step (2), the heating temperature of the drying oven is 65-75℃.

[0039] The organosilicon encapsulated quantum dot film prepared by the application has high fluorescence quantum efficiency (more than 90%), high light transmittance (more than 90% in the scattering area under 40 μm film thickness) and low surface roughness (<30 nm under 40 μm film thickness), and has great potential in the fields of display and X-ray imaging.

[0040] In addition, the preparation operation of the present application is simple and easy to operate, does not need inert atmosphere protection, does not need expensive film forming equipment, and raw materials are easy to obtain, the dispersion solvent of quantum dots can be recycled, and industrialized production is easy to realize. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 A toluene solution chart of perovskite colloidal quantum dots corresponding to the present application;

[0042] Figure 2 A UV-Vis absorption and fluorescence emission chart of the organic silicon encapsulated quantum dot film prepared in Example 1;

[0043] Figure 3 An appearance chart of the organic silicon encapsulated quantum dot film prepared in Example 1 under different thicknesses;

[0044] Figure 4 A micrograph of the organic silicon encapsulated quantum dot film prepared in Example 1;

[0045] Figure 5 A surface chart of the organic silicon encapsulated quantum dot film prepared in Example 1 under an atomic force microscope;

[0046] Figure 6 A transmittance chart of the organic silicon encapsulated quantum dot film prepared in Example 1 to UV-Vis light;

[0047] Figure 7 A fluorescence stability chart of the organic silicon and polystyrene encapsulated quantum dot film prepared in Example 1 to heat and UV radiation, a is the fluorescence stability to heat, and b is the fluorescence stability to UV radiation. DETAILED DESCRIPTION

[0048] The above description of the embodiments is only used to help understand the method of the present application and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

[0049] Example 1

[0050] The preparation method of the all-organic silicon ligand modified colloidal quantum dot fluorescence film is as follows:

[0051] 1) 0.0424 g of cesium bromide, 0.0736 g of lead bromide and 5 mL of N,N-dimethylformamide (DMF) were mixed, and then ultrasonically dispersed until completely dissolved to obtain a mixed solution, which was placed at room temperature 25℃ for standby.

[0052] 2) Add 113 mg of organic ligand A1 and 140 mg of organic ligand B1 to the mixed solution, continue stirring until completely dissolved, to obtain quantum dot precursors;

[0053] 3) Take 0.5 mL of quantum dot precursors, inject into 10 mL of toluene solution under strong stirring at room temperature, to obtain a colloidal quantum dot solution modified by full organic silicon ligands, as shown in Figure 1

[0054] The UV-visible light absorption and fluorescence emission spectra of the colloidal quantum dot solution are shown in Figure 2 Figure 2 It can be seen that the luminescent performance is excellent;

[0055] 4) Take 0.5 mL of colloidal quantum dot solution, drop coat on a clean glass slide of 2*2 cm 2 , and vacuum heat in a vacuum drying oven at 70°C, to volatilize the solvent and fully condense and crosslink the organic silicon to form a film, to obtain a uniform colloidal quantum dot fluorescence film modified by full organic silicon ligands.

[0056] The quantum dots of the present application can obtain quantum dot films of different thicknesses, and the quantum dot fluorescence films modified by full organic silicon ligands of different thicknesses have the appearance as shown in Figure 3 Figure 4 The microscopic magnified image shows that the prepared colloidal quantum dot fluorescence film modified by full organic silicon ligands does not exhibit obvious aggregation. Figure 5 The atomic force microscope image shows that the prepared film has very small surface roughness (the surface roughness of a film of about 40 μm is less than 30 nm). Figure 6 It is shown that the prepared quantum dot film encapsulated by organic silicon has very good transmittance of light in the scattering area (the transmittance of a film of about 40 μm in the scattering area is greater than 90%). In addition, compared with the film encapsulated by polystyrene under the same quantum dot solid content, the prepared quantum dot film encapsulated by organic silicon exhibits better fluorescence stability against heat and UV radiation (as shown in Figure 7

[0057] Example 2:

[0058] The preparation method of the colloidal quantum dot fluorescence film modified by full organic silicon ligands is as follows:

[0059] 1) Mix 0.0424 g of cesium bromide, 0.0736 g of lead bromide and 5 mL of N,N-dimethylformamide, and then ultrasonically disperse until completely dissolved, and place at room temperature of 25°C for standby.

[0060] 2) Add 107 mg of organic ligand A2 and 150 mg of organic ligand B3 to the above solution, continue stirring until completely dissolved, as precursors for synthesizing quantum dots.​​​​

[0061] 3) Take 0.2 mL of the precursor solution and inject it into 10 mL of toluene solution under strong stirring at room temperature, to obtain a colloidal quantum dot solution dispersed in toluene.

[0062] 4) Take 0.2 mL of the colloidal quantum dot solution and drop it on a clean glass slide of 2*2 cm 2 , and heat it in a 60°C drying oven to evaporate the solvent and fully condense and cross-link the organosilicon into a film, to finally obtain a uniform organosilicon-encapsulated quantum dot fluorescent film.

[0063] Example 3:

[0064] The preparation method of the organosilicon-encapsulated perovskite quantum dot and its fluorescent film is as follows:

[0065] 1) Mix 0.0337 g of cesium chloride, 0.0556 g of lead chloride, and 5 mL of N,N-dimethylformamide, and then ultrasonically disperse until completely dissolved, and place it at room temperature of 25°C for standby.

[0066] 2) Add 113 mg of organic ligand A1 and 140 mg of organic ligand B1 to the above solution, and continue to stir until completely dissolved, as the precursor for synthesizing quantum dots.

[0067] 3) Take 0.2 mL of the precursor solution and inject it into 10 mL of toluene solution under strong stirring at room temperature, to obtain a colloidal quantum dot solution dispersed in toluene, as shown in Figure 1 . The ultraviolet-visible light absorption and fluorescence emission spectra of the quantum dot colloidal solution are shown in Figure 2 .

[0068] 4) Take 0.5 mL of the colloidal quantum dot solution and drop it on a clean glass slide of 2*2 cm 2 , and heat it in a 70°C vacuum drying oven to evaporate the solvent and fully condense and cross-link the organosilicon into a film, to finally obtain a uniform organosilicon-encapsulated quantum dot fluorescent film.

Claims

1. A method for preparing a full-organic-silicon-ligand-modified colloidal quantum dot, comprising the following steps: 1) mixing cesium bromide, lead bromide and N, N-dimethylformamide, and ultrasonically dispersing until completely dissolved to obtain a mixed solution; the mass ratio of cesium bromide to lead bromide is (0.03-0.05):(0.06-0.08), and the mass-volume ratio of cesium bromide to N, N-dimethylformamide is (0.03-0.05):(4-10) g / mL; 2) adding organic silicon ligand A and organic silicon ligand B to the mixed solution, and continuing to stir until completely dissolved to obtain a quantum dot precursor; 3) injecting the quantum dot precursor into strongly stirred toluene at room temperature to obtain a full-organic-silicon-ligand-modified colloidal quantum dot; the volume ratio of the quantum dot precursor to toluene is (0.4-0.8):(5-15); the organic silicon ligand for the surface of the quantum dot comprises organic silicon ligand A and organic silicon ligand B, the structure of the organic silicon ligand A is shown in A1, A2 or A3: 、 、 the structure of the organic silicon ligand B is shown in B1, B2, B3 or B4: 、 、 。 2. The production method according to claim 1, characterized by, in step 2), the mass ratio of the organic silicon ligand A to the organic silicon ligand B is (100-120):(130-150).

3. The preparation method according to claim 1, characterized in that, in step 2), the mass-volume ratio of the organic silicon ligand A to N, N-dimethylformamide is (100-120):(4-10) mg / mL.

4. A method for preparing a full-organic-silicon-ligand-modified colloidal quantum dot fluorescent film, comprising the following steps: (1) taking a full-organic-silicon-ligand-modified colloidal quantum dot solution, and drop-casting it on a clean glass slide, wherein the full-organic-silicon-ligand-modified colloidal quantum dot solution is prepared by the method of claim 1; (2) transferring to a drying oven for heating, so that the solvent volatilizes and the organic silicon fully condenses and crosslinks to form a film, and finally a full-organic-silicon-ligand-modified colloidal quantum dot fluorescent film is prepared.

5. The preparation method according to claim 4, characterized in that, in step (1), the amount of the full-organic-silicon-ligand-modified colloidal quantum dot solution is 0.1-0.5 mL, and in step (2), the heating temperature of the drying oven is 65-75°C.

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