Preparation method of red light perovskite quantum dot with core-shell structure

Abstract

The invention provides a preparation method of a red light perovskite quantum dot with a core-shell structure, and belongs to the technical field of quantum dot preparation. According to the method, a CsPbI3 quantum dot coarse solution and a cadmium sulfide precursor solution are mixed, stirred and heated to a certain temperature, cadmium sulfide grows on the surface of the quantum dot in an epitaxial mode, the red light CsPbI3 / CdS core-shell quantum dot is prepared, the formation of a core-shell structure is beneficial to passivation of defects on the surface of the quantum dot, and meanwhile ion migration and Auger recombination of the quantum dot are inhibited. The invention provides a solution for preparing the red light perovskite quantum dot light-emitting diode with high external quantum efficiency, long service life and low efficiency roll-off.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of quantum dot preparation, and particularly relates to a preparation method of red light perovskite quantum dots with a core-shell structure. BACKGROUND

[0002] CsPbI3 perovskite quantum dots with red light emission are considered to be a strong competitor of rare earth and organic light-emitting materials due to advantages such as narrow emission spectrum, high defect tolerance, wide color gamut and simple preparation process, and have great development potential and application value in the display field. In recent years, they have attracted the attention of governments and international academia and industry.

[0003] Although CsPbI3 quantum dots show excellent defect tolerance, their ionic conduction characteristics and surface defect states make them very prone to ion migration under an electric field, thereby reducing the electroluminescent performance and stability of light-emitting diodes. At present, the main means to inhibit ion migration of CsPbI3 quantum dots is to passivate their surface defects by external ligands and to increase the activation energy of iodine ion migration, but this method is not ideal for inhibiting ion migration. On the other hand, the high exciton binding energy of quantum dots will cause serious Auger recombination, which reduces the radiation recombination rate and generates a large amount of Joule heat, which is also not conducive to the improvement of device working efficiency and service life.

[0004] Therefore, developing a new method that can effectively passivate the surface defects of CsPbI3 quantum dots while inhibiting their ion migration and Auger recombination is crucial for obtaining red light perovskite quantum dot light-emitting diodes with high external quantum efficiency, long running life and low efficiency roll-off. SUMMARY

[0005] In view of the problems in the background art, the purpose of the present application is to provide a preparation method of red light perovskite quantum dots with a core-shell structure. The method mixes and stirs a CsPbI3 quantum dot crude solution with a cadmium sulfide precursor solution and heats it to a certain temperature, allowing cadmium sulfide to grow epitaxially on the surface of the quantum dots, to prepare red light CsPbI3 / CdS core-shell quantum dots. The formation of the core-shell structure helps to passivate the defects on the surface of the quantum dots, while inhibiting their ion migration and Auger recombination.

[0006] To achieve the above-mentioned purpose, the technical solution of the present application is as follows:

[0007] A preparation method of red light perovskite quantum dots with a core-shell structure, comprising the following steps:

[0008] Step 1. Prepare a red light CsPbI3 quantum dot crude solution;

[0009] Step 2. Shell epitaxial growth: the red light CsPbI3 quantum dot crude solution prepared in step 1 is warmed to 50-60 ℃, then cadmium sulfide precursor solution is added thereto, stirring, and the solution temperature is increased to 95-105 ℃ at a certain temperature increasing rate, then it is immediately taken out and placed in an ice water bath for stirring cooling to room temperature, thereby obtaining a red light CsPbI3 / CdS core-shell quantum dot crude solution;

[0010] Step 3. Methyl acetate is added to the red light CsPbI3 / CdS core-shell quantum dot crude solution, then centrifugal treatment is performed, the precipitate obtained by centrifugation is dispersed in a non-polar solvent, methyl acetate is added again, centrifugal treatment is performed again, then the precipitate obtained is re-dispersed in a non-polar solvent, thereby obtaining a red light CsPbI3 / CdS core-shell quantum dot dispersion.

[0011] Further, the specific process for preparing the red light CsPbI3 quantum dot crude solution in step 1 is as follows:

[0012] Step 1.1. Cesium carbonate and oleic acid are sequentially added to octadecene, stirring, and gradient heating is performed under vacuum, then nitrogen replacement is performed, thereby obtaining a first precursor solution;

[0013] Step 1.2. Lead iodide and zinc iodide are mixed with octadecene, then gradient heating is performed on the mixture under vacuum, nitrogen replacement is performed, then oleic acid and oleylamine are added, stirring, thereby obtaining a second precursor solution;

[0014] Step 1.3. The temperature of the second precursor solution is set to 165-175 ℃, the first precursor solution is added to the second precursor solution under a nitrogen environment, after a certain period of incubation, it is taken out and placed in an ice water bath for stirring cooling to room temperature, thereby obtaining a red light CsPbI3 quantum dot crude solution.

[0015] Further, in step 1.1, the mass of cesium carbonate to the volume of octadecene is 18-22 mg / mL, and the volume of oleic acid to the volume of octadecene is 0.12-0.16; in step 1.2, the mass of lead iodide to the volume of octadecene is 34-36 mg / mL, the mass of zinc iodide to the volume of octadecene is 71-73 mg / mL, the volume ratio of oleic acid to octadecene is 0.55-0.65, and the volume ratio of oleylamine to octadecene is 0.55-0.65.

[0016] Further, the gradient heating conditions of step 1.1 are sequentially at 40 ℃, 60 ℃, and 100 ℃, each temperature stage is maintained for 10 minutes; the gradient heating conditions of step 1.2 are sequentially at 40 ℃, 60 ℃, 100 ℃, and 120 ℃, each temperature stage is maintained for 10 minutes.

[0017] Further, in step 2, the temperature rising rate is 9-18 ℃ / min.

[0018] Further, in step 2, the volume ratio of the red light CsPbI3 quantum dot crude solution and the cadmium sulfide precursor solution is 51-94.

[0019] Further, in step 2, the preparation process of the cadmium sulfide precursor solution is: adding cadmium diethyldithiocarbamate into a container containing oleylamine and a non-polar solvent, and after fully shaking, the cadmium sulfide precursor solution is obtained; wherein the volume ratio of oleylamine and non-polar solvent is 1:1, and the mass of cadmium diethyldithiocarbamate and the volume of oleylamine are in the proportion of 72-92 mg / mL.

[0020] Further, the non-polar solvent is one of n-octane, n-hexane and toluene.

[0021] Further, in step 3, the volume of the first added methyl acetate is 45-55 mL, the volume of the first added non-polar solvent is 1 mL, the volume of the second added methyl acetate is 2-3 mL, and the volume of the second added non-polar solvent is 0.4-0.6 mL.

[0022] Further, the non-polar solvent is one or several of n-octane, n-hexane and toluene.

[0023] In summary, due to the adoption of the above technical solutions, the present application has the following beneficial effects:

[0024] The application discloses a preparation method of red light perovskite quantum dots with a core-shell structure. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The chemical structural formula of cadmium diethyldithiocarbamate.

[0026] Figure 2 The preparation mechanism diagram of the CsPbI3 / CdS core-shell quantum dots.

[0027] Figure 3Photoluminescence spectrum and ultraviolet-visible absorption spectrum of red light perovskite quantum dots; (a) is the photoluminescence spectrum and ultraviolet-visible absorption spectrum of red light CsPbI3 quantum dots synthesized by the comparative example, and (b) is the photoluminescence spectrum and ultraviolet-visible absorption spectrum of red light CsPbI3 / CdS core-shell quantum dots synthesized by Example 1.

[0028] Figure 4 Transmission electron microscope image and size distribution histogram of red light perovskite quantum dots; (a) is the transmission electron microscope image of red light CsPbI3 quantum dots synthesized by the comparative example, (b) is the transmission electron microscope image of red light CsPbI3 / CdS core-shell quantum dots synthesized by Example 1, (c) is the size distribution histogram of red light CsPbI3 quantum dots synthesized by the comparative example, and (d) is the size distribution histogram of red light CsPbI3 / CdS core-shell quantum dots synthesized by Example 1. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with embodiments and drawings.

[0030] Example 1

[0031] A preparation method of red light perovskite quantum dots with core-shell structure, comprising the following steps:

[0032] Step 1. Preparation of red light CsPbI3 quantum dot crude solution, the specific process is as follows:

[0033] Step 1.1. Add 10 mL of octadecene, 1.4 mL of oleic acid and 200 mg of cesium carbonate into a three-necked flask, transfer to a heating jacket, then stir at a speed of 300 revolutions per minute, perform gradient heating in a vacuum environment, and the step temperatures are 40℃, 60℃ and 100℃ respectively, and the time intervals are all 10 minutes; then use a hileck line to replace the gas environment in the three-necked flask with nitrogen, repeat the operation for 3 times, maintain the nitrogen atmosphere, and obtain a first precursor solution;

[0034] Step 1.2. 10 mL of octadecene, 350 mg of lead iodide and 720 mg of zinc iodide were added into another three-neck flask, which was transferred into a heating mantle and stirred at 400 rpm, and gradient heating was performed in a vacuum environment with step temperatures of 40 ℃, 60 ℃, 100 ℃ and 120 ℃, and the time interval was 10 minutes; then the gas environment in the three-neck flask was replaced with nitrogen by using a helium line, and the operation was repeated 3 times to maintain a nitrogen atmosphere; then 6 mL of oleic acid and 6 mL of oleylamine were sequentially injected into the three-neck flask, and the stirring speed was increased to 700 rpm; when the solution in the three-neck flask became clear and transparent, a second precursor solution was obtained;

[0035] Step 1.3. The second precursor solution was heated to 170 ℃ under a nitrogen atmosphere, 1.6 mL of the first precursor solution was quickly injected into the second precursor solution, and the three-neck flask was taken out and placed in an ice water bath after 5 seconds of incubation, and the solution was cooled to room temperature by magnetic stirring to obtain a red-light CsPbI3 quantum dot crude solution;

[0036] Step 2. Preparation of a cadmium sulfide precursor solution: 41 mg of cadmium diethyl dithiocarbamate was added to a vial containing 0.5 mL of oleylamine and 0.5 mL of n-octane, and the vial was shaken to obtain a cadmium sulfide precursor solution;

[0037] Step 3. The red-light CsPbI3 quantum dot crude solution obtained in step 1 was heated to 55 ℃, and then 0.36 mL of the cadmium sulfide precursor solution prepared in step 2 was added thereto, and the solution was stirred for 1 minute; then the temperature of the crude solution was increased to 100 ℃ at a rate of 12 ℃ / min, and then the three-neck flask was quickly taken out and placed in an ice water bath again to cool to room temperature, thereby obtaining a red-light CsPbI3 / CdS core-shell quantum dot crude solution;

[0038] Step 4. In a centrifuge tube, 50 mL of methyl acetate was added to the obtained red-light CsPbI3 / CdS core-shell quantum dot crude solution as an anti-solvent, and centrifugation was performed at a speed of 10,000 rpm for 1 minute; the supernatant was discarded, 1 mL of n-octane was added to the precipitate, and the mixture was shaken; then 2.5 mL of methyl acetate was added as an anti-solvent, and centrifugation was performed at a speed of 12,000 rpm for 1 minute; the supernatant was discarded, and the precipitate was dispersed with 0.5 mL of n-octane, thereby obtaining a red-light CsPbI3 / CdS core-shell quantum dot dispersion.

[0039] Example 2

[0040] A red light CsPbI3 / CdS core-shell quantum dot dispersion was prepared according to the procedure of Example 1, only adjusting the ratio of the mass of cesium carbonate to the volume of octadecene in step 1.1 to 18 mg / mL, the volume ratio of oleic acid to the volume of octadecene to 0.12, the ratio of the mass of lead iodide to the volume of octadecene in step 1.2 to 34 mg / mL, the mass of zinc iodide to the volume of octadecene to 71 mg / mL, the volume of oleic acid to the volume of octadecene to 0.55, and the volume of oleylamine to the volume of octadecene to 0.55; the temperature of the second precursor solution in step 1.3 was adjusted to 165 °C;

[0041] The mass of cadmium diethyl dithiocarbamate to the volume of oleylamine in step 2 was adjusted to 72 mg / mL;

[0042] The temperature of the red light CsPbI3quantum dot crude solution in step 3 was adjusted to 50 °C, the volume ratio of the red light CsPbI3quantum dot crude solution to the cadmium sulfide precursor solution was adjusted to 51, and then the crude solution temperature was raised to 95 °C at a temperature rise rate of 9 °C / min;

[0043] In step 4, the volume of the first addition of methyl acetate was adjusted to 45 mL, the second addition of non-polar solvent was adjusted to n-hexane, the volume was still 1 mL, the volume of the second addition of methyl acetate was adjusted to 2 mL, the second addition of non-polar solvent was adjusted to n-hexane, and the volume was adjusted to 0.4 mL; the other steps were unchanged.

[0044] Example 3

[0045] A red light CsPbI3 / CdS core-shell quantum dot dispersion was prepared according to the procedure of Example 1, only adjusting the ratio of the mass of cesium carbonate to the volume of octadecene in step 1.1 to 22 mg / mL, the volume ratio of oleic acid to the volume of octadecene to 0.16; the ratio of the mass of lead iodide to the volume of octadecene in step 1.2 to 36 mg / mL, the mass of zinc iodide to the volume of octadecene to 73 mg / mL, the volume of oleic acid to the volume of octadecene to 0.65, and the volume of oleylamine to the volume of octadecene to 0.65; the temperature of the second precursor solution in step 1.3 was adjusted to 175 °C;

[0046] The mass of cadmium diethyl dithiocarbamate to the volume of oleylamine in step 2 was adjusted to 92 mg / mL;

[0047] The temperature of the red light CsPbI3 quantum dot crude solution in step 3 is adjusted to 60 ℃, the volume ratio of the red light CsPbI3 quantum dot crude solution and the cadmium sulfide precursor solution is adjusted to 94, and then the temperature of the crude solution is raised to 105 ℃ at a temperature raising rate of 18 ℃ / min;

[0048] In step 4, the volume of the first methyl acetate is adjusted to 55 mL, the second non-polar solvent is adjusted to toluene, the volume is still 1 mL, the volume of the second methyl acetate is adjusted to 3 mL, the second non-polar solvent is adjusted to toluene, and the volume is adjusted to 0.6 mL; the other steps remain unchanged.

[0049] Comparative example

[0050] The red light CsPbI3 / CdS core-shell quantum dot dispersion liquid is prepared according to the steps of example 1, only the steps 2 and 3 are not performed, the volume of the first methyl acetate in step 4 is adjusted to 80 mL, and the other steps remain unchanged.

[0051] Figure 1 It is the chemical structural formula of cadmium diethyl dithiocarbamate, which is a precursor molecule of cadmium sulfide. In the figure, the diethyl dithiocarbamate ion is negatively charged, and can form stable coordination with the positively charged lead dangling bond in the CsPbI3 quantum dot. The cadmium ion is positively charged, and can form stable coordination with the negatively charged iodine dangling bond of the CsPbI3 quantum dot, which provides favorable conditions for the epitaxial growth of cadmium sulfide.

[0052] Figure 2 It is a preparation mechanism diagram of CsPbI3 / CdS core-shell quantum dots. Cadmium sulfide as a shell material usually needs to be epitaxially grown at high temperature or in an environment containing a large amount of base. However, the soft lattice characteristics of perovskite quantum dots make them unable to be stable in such extreme environment. The surface of the CsPbI3 quantum dots grown in the iodine-rich environment tends to adsorb the oil amine ligand, which helps to reduce the epitaxial growth temperature of the cadmium sulfide shell. Specifically, the red light CsPbI3 quantum dot crude solution obtained by hot injection method is added with a cadmium sulfide precursor which can be partially ionized into cadmium ions and diethyl dithiocarbamate ions, and stirring is performed to form stable coordination between the cadmium ions and the iodine dangling bond of the quantum dots, and stable coordination between the diethyl dithiocarbamate ions and the lead dangling bond; then the crude solution is heated to 95~105 ℃, at which time the abundant oil amine ligand on the surface of the quantum dots will induce the cadmium sulfide precursor to epitaxially grow into a cadmium sulfide shell. The formation of the shell helps to inhibit the Auger recombination and ion migration of the CsPbI3 quantum dots while improving the stability thereof.

[0053] Figure 3The photoluminescence spectrum and the ultraviolet-visible absorption spectrum of the red light perovskite quantum dots, (a) is the red light CsPbI3 quantum dots synthesized in the comparative example, (b) is the red light CsPbI3 / CdS core-shell quantum dots synthesized in Example 1. As shown in the figure, the photoluminescence peak of the CsPbI3 / CdS core-shell quantum dots prepared in Example 1 is 647 nm, and the full width at half maximum is 35 nm; the photoluminescence peak of the CsPbI3 quantum dots synthesized in the comparative example is 642 nm, and the full width at half maximum is 32 nm; although the photoluminescence peak of the CsPbI3 / CdS core-shell quantum dots has a certain red shift, and the full width at half maximum is slightly broadened, it is still in the red light band. Compared with the quantum dots synthesized in the comparative example, the first exciton absorption peak of the CsPbI3 / CdS core-shell quantum dots synthesized in Example 1 is red-shifted from 622 nm to 634 nm, which is due to the delocalization of the electron and hole wave functions generated by the photoexcitation into the shell material, resulting in a decrease in the kinetic energy of the exciton, thereby reducing the band gap of the quantum dots. At the same time, the Stokes shift of the CsPbI3 / CdS core-shell quantum dots synthesized in Example 1 is reduced from 20 nm to 13 nm, indicating a decrease in non-radiative recombination of the quantum dots.

[0054] Figure 4 The transmission electron microscopy image and size distribution histogram of the red light perovskite quantum dots, (a) and (c) are the red light CsPbI3 quantum dots synthesized in the comparative example, (b) and (d) are the red light CsPbI3 / CdS core-shell quantum dots synthesized in Example 1, wherein the insets in (a) and (b) are high-resolution transmission electron microscopy images. As shown in the figure, the interplanar spacing of the surface of the red light CsPbI3 / CdS core-shell quantum dots synthesized in Example 1 has changed obviously, from the (002) crystal face (0.31 nm) belonging to the cubic phase of CsPbI3 to the (001) crystal face (0.54 nm) and the (002) crystal face (0.27 nm) belonging to the cubic phase of sphalerite cadmium sulfide, and at the same time, the average size of the quantum dots is also increased from 5.35 nm to 6.06 nm. These facts show that the cadmium sulfide is successfully epitaxially grown on the surface of the quantum dots, and the cadmium sulfide shell is combined with the quantum dots in a wurtzite structure Figure 3 It can be seen that the quantum dots are still CsPbI3, and the cadmium sulfide shell grown on the surface does not change the morphology of the quantum dots, which is still a regular cube.

[0055] The above is only a specific implementation of the present application, any feature disclosed in this specification can be replaced by other equivalent or similar purpose alternative features unless specifically described; all features disclosed, or steps in all methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for preparing red perovskite quantum dots with a core-shell structure, characterized in that, Includes the following steps: Step 1. Prepare a crude solution of red-light-emitting CsPbI3 quantum dots; Step 2. Shell epitaxial growth: The crude red CsPbI3 quantum dot solution prepared in Step 1 is heated to 50-60 °C, and then a cadmium sulfide precursor solution is added to it. The mixture is stirred and the temperature of the solution is raised to 95-105 °C at a certain heating rate. The solution is then immediately removed and placed in an ice-water bath to be stirred and cooled to room temperature to obtain the crude red CsPbI3 / CdS core-shell quantum dot solution. Step 3. Add methyl acetate to the crude solution of red-light CsPbI3 / CdS core-shell quantum dots, then centrifuge. Disperse the precipitate obtained by centrifugation in a non-polar solvent, add methyl acetate again, centrifuge again, and then redisperse the precipitate in a non-polar solvent to obtain a dispersion of red-light CsPbI3 / CdS core-shell quantum dots.

2. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 1, characterized in that, The specific process for preparing the crude solution of red-light CsPbI3 quantum dots in step 1 is as follows: Step 1.

1. Cesium carbonate and oleic acid are added to octadecene sequentially, stirred, and subjected to gradient heating under vacuum conditions, followed by nitrogen purging to obtain the first precursor solution; Step 1.

2. After mixing lead iodide, zinc iodide and octadecene, the mixture is heated under vacuum with a gradient, then replaced with nitrogen, and then oleic acid and oleylamine are added and stirred to obtain the second precursor solution. Step 1.

3. Set the temperature of the second precursor solution to 165~175 ℃. Under nitrogen atmosphere, add the first precursor solution to the second precursor solution, keep it warm for a period of time, take it out, put it in an ice water bath and stir to cool to room temperature to obtain a crude solution of red CsPbI3 quantum dots.

3. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 2, characterized in that, In step 1.1, the mass ratio of cesium carbonate to octadecene is 18-22 mg / mL, and the volume ratio of oleic acid to octadecene is 0.12-0.

16. In step 1.2, the mass ratio of lead iodide to octadecene is 34-36 mg / mL, the mass ratio of zinc iodide to octadecene is 71-73 mg / mL, the volume ratio of oleic acid to octadecene is 0.55-0.65, and the volume ratio of oleylamine to octadecene is 0.55-0.

65.

4. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 2, characterized in that, The gradient heating conditions in step 1.1 are 40 ℃, 60 ℃, and 100 ℃ in sequence, with each temperature stage held for 10 minutes; the gradient heating conditions in step 1.2 are 40 ℃, 60 ℃, 100 ℃, and 120 ℃ in sequence, with each temperature stage held for 10 minutes.

5. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 1, characterized in that, In step 2, the heating rate is 9~18 ℃ / min.

6. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 1, characterized in that, In step 2, the volume ratio of the crude red CsPbI3 quantum dot solution to the cadmium sulfide precursor solution is 51-94.

7. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 1, characterized in that, In step 2, the preparation process of the cadmium sulfide precursor solution is as follows: Cadmium diethyldithiocarbamate is added to a container containing oleylamine and a non-polar solvent, and after thorough shaking, a cadmium sulfide precursor solution is obtained; wherein, the volume ratio of oleylamine and the non-polar solvent is 1:1, and the mass ratio of cadmium diethyldithiocarbamate to the volume ratio of oleylamine is 72~92 mg / mL.

8. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 7, characterized in that, The nonpolar solvent is one of n-octane, n-hexane, or toluene.

9. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 1, characterized in that, In step 3, the volume of methyl acetate added for the first time is 45-55 mL, the volume of non-polar solvent added for the first time is 1 mL, the volume of methyl acetate added for the second time is 2-3 mL, and the volume of non-polar solvent added for the second time is 0.4-0.6 mL.

10. The method for preparing red perovskite quantum dots with a core-shell structure as described in claim 9, characterized in that, The nonpolar solvent is one or more of n-octane, n-hexane, and toluene.

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