Preparation method and application of blue light CsPbBr3 perovskite quantum dots

Abstract

The application aims to provide a preparation method and application of blue light CsPbBr3 perovskite quantum dots, and belongs to the technical field of quantum dot preparation. The method uses a heterogeneous ligand exchange strategy to introduce 1-ethyl-3-methyl imidazole hexafluorophosphate molecules on the surface of quantum dots, and simultaneously realizes passivation of defects on the surface of quantum dots and inhibition of Auger recombination, thereby improving the optical performance and stability of the quantum dots, and the photoluminescence quantum yield is increased from 78% to 92%; a blue light emitting diode prepared based on the CsPbBr3 quantum dots realizes a maximum external quantum efficiency of 20.02% under a luminance of 6441 cd / m 2 , and still has an external quantum efficiency of nearly 19% under a high luminance of nearly 10000 cd / m 2 ; under an initial luminance of 106 cd / m 2 , a running half-life of nearly 700 minutes is obtained; and the preparation of a blue light perovskite quantum dot light emitting diode with high external quantum efficiency, high luminance, long running life and low efficiency roll-off is realized.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot preparation technology, and relates to the preparation of blue light perovskite quantum dots, specifically to a method for preparing blue light CsPbBr3 perovskite quantum dots and their application. Background Technology

[0002] Information display technology is an important measure of a country's informatization level. Active light-emitting diode (ALD)-based display technology, with its advantages of high brightness, vibrant colors, and energy efficiency, has become the mainstream development path for information display technology. As one of the three primary colors in display technology, the performance of blue light-emitting diodes directly determines the display quality. Cesium lead halide perovskite (CsPbX3, X = Cl, Br, I) quantum dots, as a novel luminescent material, have shown great potential in the field of next-generation high-definition displays due to their narrow emission bandwidth, high defect tolerance, wide color gamut, and simple synthesis process. They are considered a strong competitor to rare earth materials and organic light-emitting materials.

[0003] Currently, there are two main methods for preparing blue-emitting cesium lead halide perovskite quantum dots: mixed halogen component engineering and strong quantum confinement effect. Mixed halogen component engineering remains the most commonly used method for synthesizing blue-emitting perovskite quantum dots, but it still faces many bottlenecks. For example, under the influence of external fields such as electric fields and light fields, the blue-emitting mixed halide perovskite (CsPbBr) does not readily emit light. 3-x Cl x Halogen ions in quantum dots readily migrate, causing irreversible shifts in the spectra of the quantum dots and their devices, thus reducing color purity. In contrast, blue CsPbBr3 quantum dots synthesized using strong quantum confinement effects effectively solve this problem. 3-x Cl x The problem of poor spectral stability of quantum dots. However, as the size of quantum dots decreases, their specific surface area increases continuously, thereby exacerbating the impact of surface defects on blue CsPbBr3 quantum dots and Auger recombination.

[0004] Therefore, developing a new method to effectively passivate surface defects of blue CsPbBr3 quantum dots, stabilize the quantum dot surface, and suppress Auger recombination is crucial for improving the optical performance and stability of blue perovskite quantum dots and the performance of light-emitting diodes based on them. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a method for preparing and applying blue CsPbBr3 perovskite quantum dots. The method of the present invention utilizes a heterogeneous ligand exchange strategy to introduce 1-ethyl-3-methylimidazolium hexafluorophosphate onto the surface of the quantum dots, simultaneously achieving passivation of surface defects and suppression of Auger recombination, thereby improving the optical performance and stability of the quantum dots. This results in the fabrication of blue perovskite quantum dot light-emitting diodes with high external quantum efficiency, high brightness, long lifetime, and low efficiency roll-off.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing blue CsPbBr3 perovskite quantum dots includes the following steps:

[0008] Step 1. Prepare a crude solution of blue-light-emitting CsPbBr3 quantum dots;

[0009] Step 2. Add the obtained blue CsPbBr3 quantum dot crude solution and methyl acetate to a centrifuge tube in sequence, 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 the first quantum dot dispersion.

[0010] Step 3. Add 1-ethyl-3-methylimidazolium hexafluorophosphate to the reaction vessel, then add the first quantum dot dispersion, stir, and filter to obtain a blue CsPbBr3 perovskite quantum dot dispersion.

[0011] Furthermore, the mass ratio of 1-ethyl-3-methylimidazolium hexafluorophosphate to the volume of the first quantum dot dispersion is 5~17 mg / mL.

[0012] Furthermore, the specific process for preparing the crude blue CsPbBr3 quantum dot solution in step 1 is as follows:

[0013] Step 1.1. Cesium carbonate and oleic acid are added to octadecene in sequence, stirred, and heated under vacuum conditions with a gradient. Then, nitrogen is used to replace the atmosphere of the reaction vessel with nitrogen to obtain the first precursor solution.

[0014] Step 1.2. After mixing lead bromide, zinc bromide 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.

[0015] Step 1.3. Set the temperature of the second precursor solution to 115~125 ℃. Under nitrogen atmosphere, add the first precursor solution to the second precursor solution. After keeping it at this temperature for a period of time, take it out and place it in an ice-water bath to stir and cool to room temperature to obtain a crude solution of blue CsPbBr3 quantum dots. The volume ratio of the second precursor to the first precursor is 11~14.

[0016] Further, in step 1.1, the mass ratio of cesium carbonate to octadecene is 8-12 mg / mL, and the volume ratio of oleic acid to octadecene is 0.06-0.08; in step 1.2, the mass ratio of lead bromide to octadecene is 13-15 mg / mL, the mass ratio of zinc bromide to octadecene is 67-69 mg / mL, the volume ratio of oleic acid to octadecene is 0.45-0.55, and the volume ratio of oleylamine to octadecene is 0.45-0.55.

[0017] Further, in step 1.1, the gradient heating conditions are 40 ℃, 60 ℃, and 100 ℃ in sequence, with each temperature stage held for 10 minutes; in step 1.2, the gradient heating conditions are 40 ℃, 60 ℃, 100 ℃, and 120 ℃ in sequence, with each temperature stage held for 10 minutes.

[0018] Further, in step 2, the volume ratio of methyl acetate to the crude quantum dot solution added for the first time is 3.4 to 4.0, the volume of the non-polar solvent added for the first time is 1 mL, the volume of methyl acetate added for the second time is 2 to 3 mL, and the volume of the non-polar solvent added for the second time is 0.4 to 0.6 mL; the non-polar solvent is one or more of n-octane, n-hexane, and toluene.

[0019] This invention also provides the application of blue CsPbBr3 perovskite quantum dots obtained by the above preparation method in blue light-emitting diodes.

[0020] Furthermore, the fabrication process of the blue light-emitting diode is as follows:

[0021] S1. Preparation of poly(3,4-ethylenedioxythiophene)polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) thin films on indium tin oxide-glass substrates;

[0022] S2. Blue CsPbBr3 perovskite quantum dot dispersion was spin-coated onto the surface of a poly(3,4-ethylenedioxythiophene)polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film to obtain a perovskite quantum dot film;

[0023] S3. A patterned mask is coated on the surface of a perovskite quantum dot film, and then vacuum thermal evaporation is performed to sequentially deposit 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, lithium fluoride, and electrodes on the surface of the perovskite quantum dot film at a evaporation rate of 0.2~0.4 Å / s, thereby obtaining the desired blue light-emitting diode based on perovskite quantum dots.

[0024] Furthermore, in S1, the specific preparation process of the poly(3,4-ethylenedioxythiophene)polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film is as follows:

[0025] Clean the indium tin oxide-glass substrate, dry it with a nitrogen gun, and then treat the substrate with ultraviolet-ozone.

[0026] An aqueous solution of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate was spin-coated onto the surface of an indium tin oxide-glass substrate that had undergone UV-ozone treatment, and then annealed at 145-155 °C for 8-12 minutes, followed by cooling to room temperature.

[0027] Then, spin-coat a poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)chlorobenzene solution (4~6 mg / mL) onto the surface of the poly(3,4-ethylenedioxythiophene)polystyrene sulfonate film, and anneal it at 145~155 ℃ for 13~17 minutes. After annealing, cool to room temperature to obtain a poly(3,4-ethylenedioxythiophene)polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film on an indium tin oxide-glass substrate.

[0028] Furthermore, in S3, the thickness of the 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene layer is 45~55 nm, the thickness of the lithium fluoride layer is 0.9~1.1 nm, and the thickness of the electrode is 100 nm.

[0029] The mechanism of this invention is as follows:

[0030] This invention employs a heterogeneous ligand exchange strategy to introduce 1-ethyl-3-methylimidazolium hexafluorophosphate molecules, replacing some of the original oleic acid and oleylamine on the quantum dot surface to stabilize it. 1-ethyl-3-methylimidazolium hexafluorophosphate can partially ionize in nonpolar solvents into 1-ethyl-3-methylimidazolium cations and hexafluorophosphate ions. The hexafluorophosphate ions can form strong bonds with the lead dangling bonds and cesium sites of the quantum dots, while their large steric hindrance weakens the coupling effect between quantum dots. The 1-ethyl-3-methylimidazolium cation bonds with the bromine dangling bonds of the quantum dots, passivating surface defects and significantly suppressing Auger recombination, thus jointly improving the optical properties and stability of the quantum dots.

[0031] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0032] 1. The photoluminescence spectrum of the CsPbBr3 quantum dots prepared by this invention is 475 nm, which belongs to the blue light band; the quantum dots have excellent optical properties and stability, the photoluminescence quantum yield is increased from 78% to 92%, and the preparation method is simple and easy to operate.

[0033] 2. The blue light-emitting diode fabricated based on the CsPbBr3 quantum dots of this invention achieved a maximum external quantum efficiency (20.02%) at a brightness of 6441 cd / m², and approached 10000 cd / m². 2 Even at high brightness, it still maintains an external quantum efficiency of nearly 19%, which is among the industry's leading levels; at 106 cd / m²... 2 At its initial brightness, it achieved an operating half-life of nearly 700 minutes (the operating time corresponding to the brightness of the light-emitting diode decaying to half of its initial value), which is 125 times that of an unoptimized blue quantum dot-based light-emitting diode. Attached Figure Description

[0034] Figure 1 The adsorption energies are those of hexafluorophosphate ions and 1-ethyl-3-methylimidazolium ions on the surface of CsPbBr3 quantum dots.

[0035] Figure 2 The UV-Vis absorption and photoluminescence spectra of CsPbBr3 quantum dots synthesized in Example 1 and the comparative example are shown.

[0036] Among them, (a) is the photoluminescence spectrum of the CsPbBr3 quantum dots synthesized in the comparative example, (b) is the photoluminescence spectrum of the CsPbBr3 quantum dots synthesized in Example 1, and (c) is the ultraviolet-visible absorption spectrum of the CsPbBr3 quantum dots synthesized in Example 1 and the comparative example.

[0037] Figure 3 Scanning-transmission electron microscope images and size distribution diagrams of CsPbBr3 quantum dots synthesized in Example 1 and the comparative example;

[0038] Among them, (a) is a scanning transmission electron microscope image of the CsPbBr3 quantum dots synthesized in the comparative example, (b) is a scanning transmission electron microscope image of the CsPbBr3 quantum dots synthesized in Example 1, (c) is a size distribution diagram of the CsPbBr3 quantum dots synthesized in the comparative example, and (d) is a size distribution diagram of the CsPbBr3 quantum dots synthesized in Example 1.

[0039] Figure 4 The photoluminescence quantum yield of CsPbBr3 quantum dots synthesized in Example 1 and the comparative example is shown.

[0040] Figure 5 The femtosecond transient absorption spectra of CsPbBr3 quantum dots synthesized in Example 1 and the comparative example are shown as they change over time.

[0041] Wherein, (a) is the femtosecond transient absorption spectrum of the comparative example, and (b) is the femtosecond transient absorption spectrum of Example 1.

[0042] Figure 6 The current density-brightness-voltage curves are for blue light-emitting diodes based on CsPbBr3 quantum dots synthesized in Example 1 and the comparative example.

[0043] Figure 7 The external quantum efficiency-luminance curves are shown for blue light-emitting diodes based on CsPbBr3 quantum dots synthesized in Example 1 and the comparative example.

[0044] Figure 8 The operating half-life of the blue light-emitting diodes based on CsPbBr3 quantum dots synthesized in Example 1 and the comparative example is given. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0046] Example 1

[0047] A method for preparing blue CsPbBr3 perovskite quantum dots includes the following steps:

[0048] Step 1. Prepare a crude solution of blue CsPbBr3 quantum dots. The specific process is as follows:

[0049] Step 1.1. Add 10 mL of octadecene, 0.7 mL of oleic acid, and 100 mg of cesium carbonate to a three-necked flask, transfer to a heating mantle, and then stir at 250 rpm. Perform gradient heating in a vacuum environment with step temperatures of 40 ℃, 60 ℃, and 100 ℃, with a time interval of 10 minutes. Subsequently, replace the gas environment in the three-necked flask with nitrogen using a Schiller line to obtain the first precursor solution.

[0050] Step 1.2. Add 10 mL of octadecene, 140 mg of lead bromide, and 680 mg of zinc bromide to another three-necked flask, transfer it to a heating mantle, and then stir at 400 rpm. Perform gradient heating in a vacuum environment with step temperatures of 40 ℃, 60 ℃, 100 ℃, and 120 ℃, with each step lasting 10 minutes. Then, replace the gas environment in the three-necked flask with nitrogen using a Schiller line, and then sequentially inject 5 mL of oleic acid and 5 mL of oleylamine. Increase the stirring speed to 700 rpm. When the solution in the three-necked flask becomes clear and transparent, the second precursor solution is obtained.

[0051] Step 1.3. Take 1.6 mL of the first precursor solution and quickly inject it into the second precursor solution at a temperature of 120 °C. After holding the solution at this temperature for 5 seconds, remove the three-necked flask and place it in an ice-water bath to stir and cool it to room temperature to obtain a crude solution of blue CsPbBr3 quantum dots.

[0052] Step 2. In a centrifuge tube, add 80 mL of methyl acetate as an antisolvent to the obtained crude solution of blue CsPbBr3 quantum dots, centrifuge at 10000 rpm for 1 minute, discard the supernatant, add 1 mL of n-octane to the precipitate, shake, and then add 2.5 mL of methyl acetate as an antisolvent. Centrifuge at 12000 rpm for 1 minute, discard the supernatant, and disperse the precipitate with 0.5 mL of n-octane to obtain the first quantum dot dispersion.

[0053] Step 3. Transfer the first quantum dot dispersion to a vial containing 5 mg of 1-ethyl-3-methylimidazolium hexafluorophosphate, place the vial on a magnetic stirrer and stir at 300 rpm for 30 seconds. Then filter the quantum dot dispersion after ligand exchange using a microporous filter head to obtain a blue CsPbBr3 perovskite quantum dot dispersion.

[0054] The blue light-emitting diode was fabricated using the CsPbBr3 quantum dots synthesized in this embodiment. The specific process is as follows:

[0055] S1. Cleaning Indium Tin Oxide-Glass Substrate: First, carefully scrub the substrate with glass cleaning solution, then place the substrate in ultrapure water and anhydrous ethanol for ultrasonic cleaning for 30 minutes each. After cleaning, dry the substrate with nitrogen and place it in an ultraviolet-ozone environment for 25 minutes.

[0056] S2. Preparation of poly(3,4-ethylenedioxythiophene)polystyrene sulfonate film on clean indium tin oxide-glass substrate: The purchased poly(3,4-ethylenedioxythiophene)polystyrene sulfonate aqueous solution was uniformly spin-coated onto the surface of the indium tin oxide-glass substrate using a spin coater. The spin coating parameters were: spin speed 4000 rpm, time 40 seconds. After spin coating, the substrate was placed on a hot plate at 150 ℃ for annealing treatment for 10 minutes. After annealing, it was transferred to a petri dish and allowed to cool naturally to room temperature.

[0057] S3. Preparation of poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film by spin coating on the surface of poly(3,4-ethylenedioxythiophene)polystyrene sulfonate film: The substrate was transferred to a nitrogen glove box, and a purchased poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)chlorobenzene solution (5 mg / mL) was uniformly spin-coated onto the surface of poly(3,4-ethylenedioxythiophene)polystyrene sulfonate film using a spin coater at a speed of 4000 rpm for 45 seconds. The substrate was then transferred to a hot plate at 150°C for annealing for 15 minutes. After annealing, it was transferred to a petri dish and allowed to cool naturally to room temperature to obtain poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film.

[0058] S4. Blue CsPbBr3 quantum dot film was prepared by uniformly spin-coating a blue CsPbBr3 perovskite quantum dot dispersion onto the surface of a poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film. The spin-coating parameters were: spin speed 2000 rpm and spin time 40 seconds.

[0059] S5. A patterned mask was coated on the surface of a perovskite quantum dot film, and 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, lithium fluoride, and aluminum electrodes were sequentially deposited on its surface using a vacuum thermal evaporation method; the gas pressure inside the vacuum thermal evaporation chamber was less than 5 × 10⁻⁶. -4 A blue light-emitting diode based on CsPbBr3 quantum dots can be obtained by using a deposition rate of 0.3 Å / s, a thickness of 50 nm for 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, a thickness of 1 nm for lithium fluoride, and a thickness of 100 nm for the aluminum electrode.

[0060] Example 2

[0061] A blue light-emitting diode based on CsPbBr3 quantum dots was prepared according to the steps of Example 1, except that the mass ratio of cesium carbonate to octadecene in step 1.1 was adjusted to 8 mg / mL, the volume ratio of oleic acid to octadecene was adjusted to 0.06, the mass ratio of lead bromide to octadecene in step 1.2 was adjusted to 13 mg / mL, the mass ratio of zinc bromide to octadecene was adjusted to 67 mg / mL, the volume ratio of oleic acid to octadecene was adjusted to 0.45, and the volume ratio of oleylamine to octadecene was adjusted to 0.45; and the temperature of the second precursor solution in step 1.3 was adjusted to 115 °C.

[0062] In step 2, the volume ratio of methyl acetate to the crude quantum dot solution added for the first time was adjusted to 3.4, and the volume of methyl acetate added for the second time was adjusted to 2 mL; in step 3, the mass ratio of 1-ethyl-3-methylimidazolium hexafluorophosphate to the volume of the first quantum dot dispersion was adjusted to 5 mg / mL; the nonpolar solvent added in both steps was adjusted to n-hexane.

[0063] The annealing temperature in S2 and S3 is adjusted to 145 ℃; the annealing time in S2 is adjusted to 8 minutes and the annealing time in S3 is adjusted to 13 minutes; the concentration of the poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)chlorobenzene solution in S3 is adjusted to 4 mg / mL; in S4, the evaporation rate is adjusted to 0.2 Å / s, the thickness of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene is adjusted to 45 nm, and the thickness of lithium fluoride is 0.9 nm; other steps remain unchanged.

[0064] Example 3

[0065] A blue light-emitting diode based on CsPbBr3 quantum dots was prepared according to the steps of Example 1, except that the mass ratio of cesium carbonate to octadecene in step 1.1 was adjusted to 12 mg / mL, the volume ratio of oleic acid to octadecene was adjusted to 0.08, the mass ratio of lead bromide to octadecene in step 1.2 was adjusted to 15 mg / mL, the mass ratio of zinc bromide to octadecene was adjusted to 69 mg / mL, the volume ratio of oleic acid to octadecene was adjusted to 0.55, and the volume ratio of oleylamine to octadecene was adjusted to 0.55; and the temperature of the second precursor solution in step 1.3 was adjusted to 125 °C.

[0066] In step 2, the volume ratio of methyl acetate to the crude quantum dot solution added for the first time was adjusted to 4.0, and the volume of methyl acetate added for the second time was adjusted to 3 mL; in step 3, the mass ratio of 1-ethyl-3-methylimidazolium hexafluorophosphate to the volume of the first quantum dot dispersion was adjusted to 17 mg / mL; the nonpolar solvent added in both steps was adjusted to toluene.

[0067] The annealing temperature in S2 and S3 is adjusted to 155 ℃; the annealing time in S2 is adjusted to 12 minutes and the annealing time in S3 is adjusted to 17 minutes; the concentration of the poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)chlorobenzene solution in S3 is adjusted to 6 mg / mL; in S4, the evaporation rate is adjusted to 0.4 Å / s, the thickness of 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene is adjusted to 55 nm, and the thickness of lithium fluoride is 1.1 nm; other steps remain unchanged.

[0068] Comparative Example

[0069] Blue CsPbBr3 quantum dots and blue light-emitting diodes were prepared according to the steps in Example 1, except that step 3 was omitted.

[0070] Figure 1 The adsorption energies are those of hexafluorophosphate ions and 1-ethyl-3-methylimidazolium cations on the quantum dot surface. The negatively charged hexafluorophosphate ions tend to bond with the positively charged lead dangling bonds and cesium sites, while the positively charged 1-ethyl-3-methylimidazolium cation tends to bond with the negatively charged bromine dangling bonds. First-principles calculations show that the adsorption energies of both ions in 1-ethyl-3-methylimidazolium hexafluorophosphate on the quantum dot surface are negative, indicating that both ions bond with the quantum dot surface. The absolute value of the adsorption energy of the hexafluorophosphate ion on the quantum dot surface is significantly greater than that of the 1-ethyl-3-methylimidazolium cation (|-279.8 kcal / mol| > |-16.8 kcal / mol|), indicating a stronger bond between the hexafluorophosphate ion and the lead dangling bonds and cesium sites on the quantum dots, representing a strong bond.

[0071] Figure 2 Figure 1 shows the UV-Vis absorption and photoluminescence spectra of the CsPbBr3 quantum dots synthesized in Example 1 and the comparative example. Figure 2 shows the photoluminescence spectrum of the CsPbBr3 quantum dots synthesized in the comparative example, Figure 3 shows the photoluminescence spectrum of the CsPbBr3 quantum dots synthesized in Example 1, and Figure 4 shows the UV-Vis absorption spectra of the CsPbBr3 quantum dots synthesized in Example 1 and the comparative example. As can be seen from Figures (a) and (b), compared with the CsPbBr3 quantum dots synthesized in the comparative example, the photoluminescence peak of the CsPbBr3 quantum dots prepared in Example 1 was slightly blue-shifted by 1 nm to 475 nm, which is still in the blue light band, and the full width at half maximum (FWHM) was narrowed by 1 nm to 26 nm. Meanwhile, as can be seen from Figure (c), both the CsPbBr3 quantum dots before and after passivation with 1-ethyl-3-methylimidazolium hexafluorophosphate have obvious exciton absorption peaks, indicating that the 1-ethyl-3-methylimidazolium hexafluorophosphate molecule introduced in this invention does not change the strong quantum confinement characteristics of the quantum dots.

[0072] Figure 3 Figure 1 shows scanning transmission electron microscope (STEM) images and size distribution diagrams of CsPbBr3 quantum dots synthesized in Example 1 and the comparative example. Figure 2 shows the STEM image of the CsPbBr3 quantum dots synthesized in the comparative example, Figure 3 shows the STEM image of the CsPbBr3 quantum dots synthesized in Example 1, Figure 4 shows the size distribution diagram of the CsPbBr3 quantum dots synthesized in the comparative example, and Figure 5 shows the size distribution diagram of the CsPbBr3 quantum dots synthesized in Example 1. A comparison of Figures (a) and (b) shows that the distance between the CsPbBr3 quantum dots prepared in Example 1 is increased, which weakens the coupling effect, suppresses the fluorescence resonance energy transfer between quantum dots, and improves the luminescence performance of the quantum dots; at the same time, it has a higher degree of arrangement order (the degree of arrangement order in Example 1 is 0.94, and the degree of arrangement order in the comparative example is 0.86); in addition, the surface of the CsPbBr3 quantum dots prepared in Example 1 is almost free of metallic lead nanocrystals generated by high-energy electron irradiation (the brighter areas on the surface of the quantum dots in the figure), which means that the quantum dots synthesized in Example 1 have a more stable surface. A comparison of Figures (c) and (d) shows that the average size of the quantum dots synthesized in Example 1 is 4.0 nm, which is slightly smaller than the average size of the quantum dots synthesized in the comparative example (average size is 4.2 nm), indicating that the introduction of 1-ethyl-3-methylimidazolium hexafluorophosphate did not significantly affect the size of the quantum dots, that is, it did not weaken the confinement effect of the quantum dots.

[0073] Figure 4 The figures show the photoluminescence quantum yields of the CsPbBr3 quantum dots synthesized in Example 1 and the comparative example. As can be seen from the figures, after introducing 1-ethyl-3-methylimidazolium hexafluorophosphate onto the quantum dot surface, the photoluminescence quantum yield of the CsPbBr3 quantum dots synthesized in Example 1 increased from 78% to 92% compared to the comparative example. This indicates that the introduction of 1-ethyl-3-methylimidazolium hexafluorophosphate molecules reduces the density of trapped states on the quantum dot surface, thereby suppressing nonradiative recombination of charge carriers and increasing the radiative recombination rate of charge carriers.

[0074] Figure 5 The figures show the time-varying femtosecond transient absorption spectra of CsPbBr3 quantum dots synthesized in Example 1 and the comparative example. Figure (a) is the comparative example, and Figure (b) is Example 1. As can be seen from the figures, the replacement of the original long-chain ligand molecules on the quantum dot surface by 1-ethyl-3-methylimidazolium hexafluorophosphate significantly reduces the absorption spectrum at high excitation intensities (26 µJ / cm²). 2 The decay under the condition of ) effectively suppresses Auger recombination of CsPbBr3 quantum dots at high carrier density.

[0075] Figure 6The current density-luminance-voltage curves of blue light-emitting diodes based on CsPbBr3 quantum dots synthesized in Example 1 and the comparative example are shown. Compared with the comparative example, the blue light-emitting diode prepared in Example 1 has a lower turn-on voltage (2.6 V) and a higher luminance (13389 cd / m²). 2 This indicates that 1-ethyl-3-methylimidazolium hexafluorophosphate improves charge injection inside the light-emitting diode, making the charge injection more balanced, while stabilizing the surface of the quantum dots, enabling the device to achieve higher brightness;

[0076] Figure 7 The external quantum efficiency-luminance curves of blue light-emitting diodes based on CsPbBr3 quantum dots synthesized in Example 1 and the comparative example are shown. Compared with the comparative example, the quantum dot-based light-emitting diode prepared in Example 1 has an external quantum efficiency of 6441 cd / m². 2 A higher external quantum efficiency (20.02%) was achieved at a brightness close to 10000 cd / m². 2 Even at high brightness, it still maintains an external quantum efficiency of nearly 19%. Some tin-based and bismuth-based perovskite materials developed in recent years lag far behind cesium lead halide perovskites in photoelectric performance, making them unsuitable for the fabrication of high-performance light-emitting diodes (LEDs). The results of this invention represent a significant step towards blue perovskite LEDs for high-definition displays, setting a new world record for blue perovskite LEDs.

[0077] Figure 8 To determine the operating half-life of blue light-emitting diodes based on CsPbBr3 quantum dots synthesized in Example 1 and the comparative example, the light-emitting diode prepared in Example 1 has an operating half-life of 106 cd / m². 2 At its initial brightness, it achieved an operating half-life of nearly 700 minutes, which is 125 times that of a comparatively prepared light-emitting diode and is currently the world record for blue perovskite light-emitting diodes prepared using vacuum thermal evaporation technology.

[0078] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A method for preparing blue CsPbBr3 perovskite quantum dots, characterized in that, Comprising the following steps: Step 1. Preparation of a blue light CsPbBr3 quantum dot crude solution; Step 2. The obtained blue light CsPbBr3 quantum dot crude solution and methyl acetate are sequentially added to a centrifuge tube, then centrifugal treatment is carried out, the precipitate obtained by centrifugation is dispersed in a non-polar solvent, methyl acetate is added again, centrifugal treatment is carried out again, then the obtained precipitate is redispersed in a non-polar solvent, and a first quantum dot dispersion is obtained; Step 3. 1-ethyl-3-methylimidazolium hexafluorophosphate is added to a reaction container, then the first quantum dot dispersion is added, stirring and filtration are carried out, and a blue light CsPbBr3 perovskite quantum dot dispersion is obtained; wherein the mass of 1-ethyl-3-methylimidazolium hexafluorophosphate and the volume of the first quantum dot dispersion are in a ratio of 5-17 mg / mL.

2. The method for preparing blue CsPbBr3 perovskite quantum dots as described in claim 1, characterized in that, The specific process of Step 1 for preparing a blue light CsPbBr3 quantum dot crude solution is as follows: Step 1.

1. Cesium carbonate and oleic acid are sequentially added to octadecene, stirring is carried out, and gradient heating is carried out under vacuum conditions, then nitrogen replacement is carried out, the atmosphere of the reaction container is replaced with nitrogen, and a first precursor solution is obtained; Step 1.

2. Lead bromide and zinc bromide are mixed with octadecene, gradient heating is carried out under vacuum conditions, then nitrogen replacement is carried out, oleic acid and oleylamine are added, and stirring is carried out to obtain a second precursor solution; Step 1.

3. The temperature of the second precursor solution is set to 115-125 DEG C, the first precursor solution is added to the second precursor solution under a nitrogen environment, after a period of incubation, it is taken out, placed in an ice water bath, and stirred to cool to room temperature, and a blue light CsPbBr3 quantum dot crude solution is obtained; wherein the volume ratio of the second precursor to the first precursor is 11-14.

3. The method for preparing blue CsPbBr3 perovskite quantum dots as described in claim 2, characterized in that, In Step 1.1, the mass ratio of cesium carbonate to the volume of octadecene is 8-12 mg / mL, and the volume ratio of oleic acid to the volume of octadecene is 0.06-0.08; in Step 1.2, the mass ratio of lead bromide to the volume of octadecene is 13-15 mg / mL, the mass ratio of zinc bromide to the volume of octadecene is 67-69 mg / mL, the volume ratio of oleic acid to the volume of octadecene is 0.45-0.55, and the volume ratio of oleylamine to the volume of octadecene is 0.45-0.

55.

4. The method for preparing blue CsPbBr3 perovskite quantum dots as described in claim 2, characterized in that, In Step 1.1, the gradient heating conditions are sequentially at 40 DEG C, 60 DEG C, and 100 DEG C, and each temperature stage is maintained for 10 minutes; in Step 1.2, the gradient heating conditions are sequentially at 40 DEG C, 60 DEG C, 100 DEG C, and 120 DEG C, and each temperature stage is maintained for 10 minutes.

5. The method for preparing blue CsPbBr3 perovskite quantum dots as described in claim 1, characterized in that, In Step 2, the volume ratio of the first addition of methyl acetate to the volume of the quantum dot crude solution is 3.4-4.0, the volume of the first addition of non-polar solvent is 1 mL, the volume of the second addition of methyl acetate is 2-3 mL, and the volume of the second addition of non-polar solvent is 0.4-0.6 mL; the non-polar solvent is one or more of n-octane, n-hexane, and toluene.

6. The application of the blue light CsPbBr3 perovskite quantum dots prepared by the method of any one of claims 1-5 in a blue light emitting diode.

7. The use of blue light CsPbBr3 perovskite quantum dots in blue light emitting diodes according to claim 6, characterized in that, The preparation process of the blue light emitting diode is as follows: S1. Preparing a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film on an indium tin oxide-glass substrate; S2. Spinning a blue light CsPbBr3 perovskite quantum dot dispersion on the surface of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film to obtain a perovskite quantum dot film; S3. Covering the surface of the perovskite quantum dot film with a patterned mask plate, and then performing vacuum thermal evaporation to sequentially evaporate 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene, lithium fluoride and an electrode on the surface of the perovskite quantum dot film at a rate of 0.2-0.4 Å / s, thereby obtaining the desired blue light emitting diode based on perovskite quantum dots.

8. The use of blue light CsPbBr3 perovskite quantum dots in blue light emitting diodes according to claim 7, characterized in that, In S1, the specific preparation process of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film is as follows: The indium tin oxide-glass substrate is cleaned, dried with a nitrogen gun and subjected to ultraviolet-ozone treatment; The surface of the indium tin oxide-glass substrate after ultraviolet-ozone treatment is spun with an aqueous solution of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, annealed at a temperature of 145-155 ℃ for 8-12 minutes, and then cooled to room temperature; The surface of the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate film is further spun with a chlorobenzene solution of poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine), annealed at a temperature of 145-155 ℃ for 13-17 minutes, and then cooled to room temperature, thereby obtaining the poly(3,4-ethylenedioxythiophene) polystyrene sulfonate / poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) film on the indium tin oxide-glass substrate.

9. The use of blue light CsPbBr3perovskite quantum dots in blue light emitting diodes according to claim 7, characterized in that, In S3, the thickness of the 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene layer is 45-55 nm, the thickness of the lithium fluoride layer is 0.9-1.1 nm, and the thickness of the electrode is 100 nm.

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