Method for regulating morphology structure of perovskite quantum dot material

Abstract

The invention provides a method for regulating and controlling the morphology structure of a perovskite quantum dot material, and relates to the technical field of perovskite nanocrystal preparation. The method comprises the following steps: S1, mixing a cesium source, a lead source, octadecene and dodecylbenzene sulfonic acid, and heating and dissolving under the protection of inert gas to obtain a precursor solution containing the cesium source and the lead source; s2, dioctadecyl ammonium bromide is dissolved in 1, 3, 5-trimethylbenzene, and a precursor solution containing a bromine source is obtained; s3, mixing and cooling the two precursor solutions to obtain a quantum dot solution; and S4, centrifugally separating the crude solution, adding a mixed solvent of tert-butyl alcohol and methyl acetate in any volume ratio into the supernate, centrifugally collecting the precipitate again, and drying to obtain the CsPbBr3 quantum dot. According to the method, the morphological structure of the quantum dot is effectively regulated and controlled to be converted into a nanorod from a point, and meanwhile, good colloid structure stability is shown.

Description

Technical Field

[0001] The present invention relates to the technical field of perovskite nanocrystal preparation, and particularly to a method for regulating the morphological structure of perovskite quantum dot materials. Background Art

[0002] Semiconductor nanocrystals (NCs), especially colloidal quantum dots (QDs), have received extensive attention due to the strong correlation between their size and shape and optoelectronic properties. The size of QDs is typically between 2 - 20 nm, and the quantum confinement effect brought about by this tiny size endows them with higher color purity, luminescence intensity, and excellent stability, making them an ideal choice for optoelectronic applications. As a special type of QD material, perovskite quantum dots (PQDs) exhibit great application potential in fields such as visible light communication, solar cells, photodetectors, bioimaging, and LED devices due to their low cost, excellent stability, high photoluminescence, and high carrier mobility.

[0003] Since their first report in 2014, researchers have been committed to regulating the morphology and size of PQDs to optimize their optoelectronic properties. The regulation techniques for these PQD materials can be classified into two types. The first is carried out during their synthesis, which is mainly achieved through two methods: one is to regulate during the synthesis process, and the other is to perform post-treatment on the synthesized PQDs. The thermal injection method is one of the commonly used synthesis regulation means. This method usually involves high temperature and fast nucleation kinetics and requires the introduction of different ligands to control the growth of quantum dots. These ligands not only act as stabilizers to increase the stability of the PQD colloid but also passivate surface defects to improve the luminescence efficiency. However, excessive ligands can lead to the problem of decreased electron transport efficiency.

[0004] To solve this problem, post-treatment technology becomes crucial. The post-treatment process generally refers to the processes of adding solvents with appropriate polarity (such as ethyl acetate or methyl acetate) to the PQD colloid to remove excess surface ligands, promoting particle coalescence or crystal phase reconstruction, etc., so as to improve the applicability of PQD materials in optoelectronic devices. For example, for the PQD colloid solution synthesized using common oleic acid (OA) and oleylamine (OLA) ligands, although the luminescence performance is improved, during the post-treatment process, due to the weak binding force between oleic acid and oleylamine and the quantum dots, it is easily affected by the solution polarity and environmental factors, resulting in ligand desorption or phase transition of PQD, which affects the stability of the colloid. In addition, after the PQD synthesized with such oleic acid and oleylamine ligands undergoes 2 - 3 post-treatment processes, not only can the morphology and size of its quantum dots not be effectively regulated, but the colloid stability will also decrease significantly. Researchers found that using dodecylbenzenesulfonic acid (DBSA) with strong binding force to replace the traditional oleic acid (OA) and oleylamine (OLA) ligands can significantly enhance the colloid stability and optical properties of PQD after multiple post-treatments. However, this process usually only removes free ligands and cannot effectively remove the DBSA ligands partially bound to PQD. Even after washing 6 times, the luminous efficiency of the prepared LED devices is extremely low. Generally speaking, in the post-treatment stage, the removal of excess ligands can improve the carrier transport efficiency of PQD to a certain extent, but the removal of too many ligands will affect its colloid stability and luminescence characteristics.

[0005] Therefore, it is urgent to develop a new method for regulating the morphology and structure of quantum dots to obtain PQD materials with excellent optoelectronic properties, so as to achieve the purpose of balancing its colloid stability and electrical properties. Summary of the Invention

[0006] In view of this, the present invention proposes a method for regulating the morphology and structure of perovskite quantum dot materials to promote the stability of CsPbBr3 in an air environment and its optoelectronic transport performance.

[0007] The present invention provides a method for regulating the morphology and structure of perovskite quantum dot materials, including the following steps:

[0008] S1. Mix a cesium source, a lead source, octadecene (ODE), and dodecylbenzenesulfonic acid (DBSA), and heat and dissolve them under the protection of an inert gas to obtain a precursor solution containing the cesium source and the lead source;

[0009] S2. Dissolve dioctadecyldimethylammonium bromide (DDOAB) in 1,3,5 - trimethylbenzene to obtain a precursor solution containing a bromine source;

[0010] S3. After preheating the precursor solution containing the cesium source and the lead source in step S1, inject the precursor solution containing the bromine source in step S2 and mix them, and then cool to obtain a quantum dot solution;

[0011] S4. Centrifuge the quantum dot solution from step S3, add a post-treatment solvent to the supernatant, centrifuge to collect the precipitate, and dry it to obtain CsPbBr3 quantum dots.

[0012] The post-treatment solvent is a mixed solvent of tert-butanol and methyl acetate in any volume ratio.

[0013] In one or some possible embodiments, the volume ratio of tert-butanol to methyl acetate is 1:(0.6 - 1.5).

[0014] In one or some possible embodiments, the cesium source is selected from cesium carbonate or cesium acetate, and the lead source is selected from lead carbonate or lead acetate.

[0015] In one or some possible embodiments, in step S1, the mass-volume ratio of the cesium source, lead source, octadecene, and dodecylbenzenesulfonic acid is (0.06 - 0.15) g: 0.076 g: (5 - 25) ml: (0.5 - 1.5) ml.

[0016] In one or some possible embodiments, in step S1, the dissolution temperature is 100 - 120 °C, and the time is 1 - 1.5 h.

[0017] In one or some possible embodiments, in step S2, the mass-volume ratio of dioctadecylammonium bromide to 1,3,5-trimethylbenzene is 0.4367 g: (0.5 - 1.5) ml.

[0018] In one or some possible embodiments, in step S3, the preheating temperature is 150 - 160 °C; the mixing time is 2 - 10 min.

[0019] In one or some possible embodiments, in step S4, the centrifugation speed is 7500 - 8500 rpm, and the time is 5 - 10 min.

[0020] In one or some possible embodiments, in step S4, the drying temperature is 40 - 60 °C, and the time is 12 - 24 h.

[0021] The method for regulating the morphology and structure of perovskite quantum dot materials provided by the present invention has the following beneficial effects compared with the prior art:

[0022] (1) The post-treatment solvent (methyl acetate and tert-butanol) adopted in the present invention has a stronger washing effect on the surface ligand (DBSA) of cesium lead bromide quantum dots. While showing good colloidal structure stability, it effectively regulates the morphology and structure of quantum dots from perovskite quantum dots to perovskite nanorods.

[0023] (2) The cesium lead bromide quantum dots prepared by the present invention have been significantly improved in both optical properties (photoluminescence quantum yield, PLQY) and electrical properties (electron transport efficiency). The PLQY value of the quantum dots is as high as 85-95%, and the external quantum efficiency EQE value of the LED device prepared therefrom is as high as 9.6%. This value is nearly three times higher than that of the quantum dot thin film LED device passivated with DBSA ligand in the prior art, showing a great advantage in electron transport efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 Schematic diagram of the post-treatment process of the quantum dot solution of the present invention;

[0026] Figure 2 Post-treatment physical diagrams of CsPbBr3 quantum dots in Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0027] Figure 3 Post-treatment physical diagram of CsPbBr3 quantum dots in Comparative Example 4 of the present invention;

[0028] Figure 4 Post-treatment physical diagram of CsPbBr3 quantum dots in Comparative Example 5 of the present invention;

[0029] Figure 5 XRD test diagram of CsPbBr3 quantum dots prepared in Examples 1-3 of the present invention;

[0030] Figure 6 XRD test diagram of CsPbBr3 quantum dots prepared in Example 2 and Comparative Examples 1-4 of the present invention;

[0031] Figure 7 Ligand density change diagram of CsPbBr3 quantum dots prepared in Examples 1-3 of the present invention;

[0032] Figure 8 High-resolution transmission electron microscope atomic image structure diagram of CsPbBr3 quantum dots prepared in Examples 1-3 of the present invention;

[0033] Figure 9 High-resolution transmission electron microscope atomic image structure diagram of CsPbBr3 quantum dots prepared in Comparative Examples 1-4 of the present invention;

[0034] Figure 10 PLQY test diagrams of CsPbBr3 quantum dots prepared in Examples 1-3 of the present invention;

[0035] Figure 11 PLQY test diagrams of CsPbBr3 quantum dots prepared in Example 2 and Comparative Examples 1-4 of the present invention;

[0036] Figure 12 Schematic diagram of the LED device prepared by the present invention;

[0037] Figure 13 Graph showing the relationship between current density and voltage of the LED devices prepared in Examples 1-3 of the present invention;

[0038] Figure 14 Graph showing the relationship between current density and voltage of the LED devices prepared in Example 2 and Comparative Examples 1 and 2 of the present invention;

[0039] Figure 15 Test result diagram of the external quantum dot efficiency of the LED devices prepared in Examples 1-3 and Comparative Examples 1-2 of the present invention. Detailed implementation manners

[0040] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0041] In order to effectively regulate the morphology and structure of quantum dots during the post-treatment process in the prior art, a method of removing surface ligands and promoting particle aggregation or crystal phase reconstruction by changing the polarity of the post-treatment solution is proposed. The inventor found during the research process that: due to the ionic characteristics of PQD, it shows a high solubility in polar solvents. Generally, the greater the polarity of the solvent, the easier it is to cause the desorption of the surface ligands of the quantum dots. Therefore, the range of post-treatment solvents suitable for PQD colloidal solutions is relatively limited. Although medium-polarity solvents such as methyl acetate or ethyl acetate commonly used can partially remove surface ligands, the effect on PQD passivated by DBSA ligands with strong binding force is not ideal. If stronger polar alcohol solvents such as methanol or ethanol are used, the quantum dot structure may be damaged, affecting its stability. In view of the fact that the prior art does not meet the inventor's expectations, the inventor made the present invention through further exploration and research.

[0042] The present invention attempts to adopt a hybrid strategy, that is, to mix stronger polar tert-butanol with medium polar methyl acetate or ethyl acetate as the post-treatment solvent for the quantum dot solution. Compared with other alcohol solvents that may damage the quantum dot structure, tert-butanol has a milder polarity and is more suitable for this hybrid system. The inventors further found that by adjusting the ratio of these two solvents, the overall polarity of the post-treatment solvent can be precisely controlled, thereby effectively regulating the morphology and size of the PQD passivated by the DBSA ligand. This method not only solves the problem of difficult regulation of the morphology and structure of perovskite nanocrystal colloids during the post-treatment process, but also enables the quantum dots to self-assemble into nanorods, further optimizing their optoelectronic properties.

[0043] The technical solution for regulating the morphology and structure of perovskite quantum dot materials in the present invention includes the following steps:

[0044] S1. Mix a cesium source, a lead source, octadecene, and dodecylbenzenesulfonic acid, and heat and dissolve them under the protection of an inert gas to obtain a precursor solution containing the cesium source and the lead source;

[0045] S2. Dissolve dioctadecylammonium bromide in 1,3,5-trimethylbenzene to obtain a precursor solution containing a bromine source;

[0046] S3. After preheating the precursor solution containing the cesium source and the lead source in step S1, inject the precursor solution containing the bromine source in step S2 and mix them, and then cool to obtain a quantum dot solution;

[0047] S4. Refer to Appendix Figure 1 , centrifuge and separate the quantum dot solution in step S3, add a post-treatment solvent to the supernatant, centrifuge and collect the precipitate, and dry it to obtain CsPbBr3 quantum dots;

[0048] The post-treatment solvent is a mixed solvent of tert-butanol and methyl acetate in any volume ratio.

[0049] By adding mixed solvents with different ratios during the post-treatment process, the present invention can effectively regulate the morphology and size of quantum dots, enabling the morphology of perovskite quantum dots to self-assemble from nanocrystals into nanorods. This regulation process is attributed to the dynamics of ligand binding to the PQD surface: during the ligand detachment process, the PQD crystal is prone to preferentially grow on the facet with low binding energy. More importantly, the formation of these nanorods reduces the ligand density of the quantum dots while maintaining high optical performance, thereby effectively enhancing the electron transport efficiency of PQD devices.

[0050] The following is illustrated with specific examples. The materials and equipment involved in the examples are all commercially available conventional products without special source instructions.

[0051] Example 1

[0052] S1. Mix 0.1 g of cesium carbonate (Cs2CO3), 0.076 g of lead acetate (Pb(Ac)2), 10 ml of ODE, and 1 ml of DBSA, then heat the mixture to 100 °C under the protection of nitrogen and stir for 1 h until dissolved to remove water and oxygen, obtaining a precursor solution containing cesium source and lead source;

[0053] S2. Dissolve 0.4367 g of DDOAB in 1 ml of 1,3,5 - trimethylbenzene and shake to dissolve, obtaining a precursor solution containing bromine source;

[0054] S3. After preheating the precursor solution containing cesium source and lead source in step S1 to 155 °C, inject 1 ml of the precursor solution containing bromine source in step S2, mix and react for 2 min, then cool to room temperature in an ice - water bath to obtain a quantum dot solution;

[0055] S4. Centrifuge the quantum dot solution in step S3 at a speed of 7800 rpm for 5 min, separate and collect the supernatant to remove incompletely reacted precipitates. Add a post - treatment solvent (volume ratio 2:3) to the supernatant, centrifuge at a speed of 7500 rpm for 8 min, then separate and collect the precipitate. This process can be repeated 2 times. Finally, dry the precipitate at 50 °C for 18 h to obtain CsPbBr3 quantum dots;

[0056] The post - treatment solvent used is a mixed solvent of tert - butanol and methyl acetate with a volume ratio of 2:3.

[0057] Example 2

[0058] S1. Mix 0.1 g of Cs2CO3, 0.076 g of Pb(Ac)2, 10 ml of ODE, and 1 ml of DBSA, then heat the mixture to 100 °C under the protection of nitrogen and stir for 1 h until dissolved to remove water and oxygen, obtaining a precursor solution containing cesium source and lead source;

[0059] S2. Dissolve 0.4367 g of DDOAB in 1 ml of 1,3,5 - trimethylbenzene and shake to dissolve, obtaining a precursor solution containing bromine source;

[0060] S3. After preheating the precursor solution containing cesium source and lead source in step S1 to 155 °C, inject 1 ml of the precursor solution containing bromine source in step S2, mix and react for 2 min, then cool to room temperature in an ice - water bath to obtain a quantum dot solution;

[0061] S4. Centrifuge the quantum dot solution in step S3 at a speed of 7800 rpm for 5 min, separate and collect the supernatant to remove incompletely reacted precipitates. Add a post - treatment solvent (volume ratio 1:1) to the supernatant, centrifuge at a speed of 7500 rpm for 8 min, then separate and collect the precipitate. This process can be repeated 2 times. Finally, dry the precipitate at 50 °C for 18 h to obtain CsPbBr3 quantum dots;

[0062] The post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 1:1.

[0063] Example 3

[0064] S1. After mixing 0.1 g of Cs2CO3, 0.076 g of Pb(Ac)2, 10 ml of ODE and 1 ml of DBSA, heat the mixture to 100 °C under the protection of nitrogen and stir for 1 h until dissolved to remove water and oxygen, obtaining a precursor solution containing cesium source and lead source;

[0065] S2. Dissolve 0.4367 g of DDOAB in 1 ml of 1,3,5-trimethylbenzene and shake to dissolve, obtaining a precursor solution containing bromine source;

[0066] S3. After preheating the precursor solution containing cesium source and lead source in step S1 to 155 °C, inject 1 ml of the precursor solution containing bromine source in step S2, mix and react for 2 min, then cool to room temperature in an ice-water bath to obtain a quantum dot solution;

[0067] S4. Centrifuge the quantum dot solution in step S3 at a speed of 7800 rpm for 5 min, separate and collect the supernatant to remove the incompletely reacted precipitate. Add the post-treatment solvent (volume ratio 3:2) to the supernatant, centrifuge at a speed of 7500 rpm for 8 min, then separate and collect the precipitate. This process can be repeated 2 times. Finally, dry the precipitate at 50 °C for 18 h to obtain CsPbBr3 quantum dots;

[0068] The post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 3:2.

[0069] Example 4

[0070] S1. After mixing 0.06 g of Cs2CO3, 0.076 g of Pb(Ac)2, 5 ml of ODE and 0.5 ml of DBSA, heat the mixture to 100 °C under the protection of nitrogen and stir for 1 h until dissolved to remove water and oxygen, obtaining a precursor solution containing cesium source and lead source;

[0071] S2. Dissolve 0.4367 g of DDOAB in 0.5 ml of 1,3,5-trimethylbenzene and shake to dissolve, obtaining a precursor solution containing bromine source;

[0072] S3. After preheating the precursor solution containing cesium source and lead source in step S1 to 150 °C, inject 1 ml of the precursor solution containing bromine source in step S2, mix and react for 5 min, then cool to room temperature in an ice-water bath to obtain a quantum dot solution;

[0073] S4. Centrifuge the quantum dot solution from step S3 at 8500 rpm for 10 min, separate and collect the supernatant to remove the incompletely reacted precipitate. Add the post-treatment solvent (volume ratio 2:3) to the supernatant, centrifuge at 7500 rpm for 5 min, then separate and collect the precipitate. This process can be repeated 2 - 3 times. Finally, dry the precipitate at 50 °C for 24 h to obtain CsPbBr3 quantum dots.

[0074] The post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 2:3.

[0075] Example 5

[0076] S1. Mix 0.1 g of Cs2CO3, 0.076 g of Pb(Ac)2, 15 ml of ODE, and 1 ml of DBSA, then heat to 110 °C under the protection of nitrogen and stir for 1.2 h until dissolved to exclude water and oxygen, obtaining a precursor solution containing cesium source and lead source.

[0077] S2. Dissolve 0.4367 g of DDOAB in 1 ml of 1,3,5-trimethylbenzene and shake to dissolve, obtaining a precursor solution containing bromine source.

[0078] S3. After preheating the precursor solution containing cesium source and lead source from step S1 to 155 °C, inject 1 ml of the precursor solution containing bromine source from step S2, mix and react for 8 min, then cool to room temperature in an ice-water bath to obtain a quantum dot solution.

[0079] S4. Centrifuge the quantum dot solution from step S3 at 7500 rpm for 5 min, separate and collect the supernatant to remove the incompletely reacted precipitate. Add the post-treatment solvent (volume ratio 1:1) to the supernatant, centrifuge at 7500 rpm for 5 min, then separate and collect the precipitate. This process can be repeated 2 - 3 times. Finally, dry the precipitate at 60 °C for 12 h to obtain CsPbBr3 quantum dots.

[0080] The post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 1:1.

[0081] Example 6

[0082] S1. Mix 0.15 g of Cs2CO3, 0.076 g of Pb(Ac)2, 25 ml of ODE, and 1.5 ml of DBSA, then heat to 120 °C under the protection of nitrogen and stir for 1.5 h until dissolved to exclude water and oxygen, obtaining a precursor solution containing cesium source and lead source.

[0083] S2. Dissolve 0.4367 g of DDOAB in 1.5 ml of 1,3,5-trimethylbenzene and shake to dissolve, obtaining a precursor solution containing bromine source.

[0084] S3. After preheating the precursor solution containing cesium source and lead source in step S1 to 160 °C, 1 ml of the precursor solution containing bromine source in step S2 was injected, and after mixing and reacting for 10 min, it was cooled to room temperature in an ice-water bath to obtain a quantum dot solution;

[0085] S4. Centrifuge the quantum dot solution in step S3 at a speed of 8500 rpm for 10 min, separate and collect the supernatant to remove the incompletely reacted precipitate. Add a post-treatment solvent (volume ratio 3:2) to the supernatant, centrifuge at a speed of 7500 rpm for 5 min, separate and collect the precipitate. This process can be repeated 2 - 3 times, and finally dry the precipitate at 55 °C for 14 h;

[0086] The post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 3:2.

[0087] Comparative Example 1

[0088] The difference from Example 2 is that: only ethyl acetate was used as the post-treatment solvent, and the other steps remained unchanged.

[0089] Comparative Example 2

[0090] The difference from Example 2 is that: the post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 1:4, and the other steps remained unchanged.

[0091] Comparative Example 3

[0092] The difference from Example 2 is that: the post-treatment solvent used is a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 4:1, and the other steps remained unchanged.

[0093] Comparative Example 4

[0094] The difference from Example 2 is that: in step S1, OA and OLA were used to replace DBSA, and the other steps remained unchanged.

[0095] Comparative Example 5

[0096] The difference from Example 2 is that: isopropyl alcohol was used as the post-treatment solvent, and the other steps remained unchanged.

[0097] Record the physical pictures of the quantum dot solutions prepared in Examples 1 - 3 and Comparative Examples 1 - 5 during the post-treatment process, as Figures 2 - 4 shown.

[0098] Figure 2Three groups of physical pictures respectively show the states before, during, and after post-treatment. Each group of pictures contains 6 centrifuge tubes, which correspond to the physical pictures of the quantum dot solutions prepared in Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3, and Comparative Example 3 at different treatment stages from left to right. It can be seen from the figure that: the quantum dot solutions prepared in the examples and comparative examples can maintain a stable state before post-treatment. After the post-treatment is completed, the quantum dot solutions prepared in Comparative Examples 1-2 can still maintain stability, while the quantum dot solution prepared in Comparative Example 3 turns significantly yellow, indicating that the stability of its quantum dot solution is damaged by the polar solvent, resulting in a phase change of the quantum dot solution. From this, it can be inferred that using tert-butanol alone for post-treatment is more likely to damage the stability of quantum dots. At the same time, the quantum dot solutions of the samples in Examples 1-3 can still maintain good solution stability before and after treatment, indicating that post-treating the quantum dot solution by the method of the present invention will not cause a structural phase change.

[0099] Figure 3 From left to right, they respectively correspond to the physical pictures of the quantum dot solution prepared in Comparative Example 4 before and after post-treatment. It can be seen from the figure that: after post-treatment with a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 1:1, the color of its quantum dot solution turns yellow, indicating that its quantum dot solution has undergone a phase change. From this, it can be inferred that oleic acid and oleylamine do not have a strong binding effect on cesium lead bromide quantum dots. Therefore, the technical effect of post-treatment with the mixed solvent of the present invention is not ideal, indicating that the regulation method of the present invention has a certain pertinence and has significant advantages for ligands using DBSA.

[0100] Figure 4 From left to right, they respectively correspond to the physical pictures of the quantum dot solution prepared in Comparative Example 5 before and after post-treatment. It can be seen from the figure that: after post-treatment with isopropanol, the color of its quantum dot solution turns yellow, indicating that its result has undergone a phase change and precipitation. It shows that only using a relatively polar isopropanol solution for the post-treatment process will damage the stability of the quantum dot solution.

[0101] XRD tests were performed on the CsPbBr3 quantum dots prepared in Examples 1-3 using X-ray diffraction to observe their crystal structures. The test results are as Figure 5 shown.

[0102] From Figure 5 it can be seen that: when the ratio range of the post-treatment solvents methyl acetate and tert-butanol is adjusted to be within 2:3 to 3:2 for post-treatment, the samples in Examples 1-3 show XRD peaks of crystal plane characteristics such as (100), (110), (111), (200), (210), (211), (202), (103), etc., proving that post-treatment with the mixed solvent within this range will not affect the phase structure of CsPbBr3 quantum dots.

[0103] The XRD test was carried out on the CsPbBr3 quantum dots prepared in Comparative Examples 1-4 by using X-ray diffraction to observe their crystal structures, and the test results are as Figure 6 shown.

[0104] It can be Figure 6 seen that: when the post-treatment process of the quantum dot solution is carried out by using the mixed solvent of the present invention, when the proportion of tert-butanol is low, such as Figure 6 a and Figure 6 b, the XRD phase structure does not change, indicating that a small amount of ligand stripping does not change its crystal structure; as the proportion of tert-butanol added increases, such as Figure 6 c, the XRD phase structure changes, indicating that excessive treatment with tert-butanol easily leads to the destruction of the crystal structure; Figure 6 From the XRD pattern result of

[0105] d, it can be seen that there are impurity peaks in the CsPbBr3 quantum dots prepared in Comparative Example 4, indicating that its crystal structure begins to become unstable and is prone to phase change.

[0105] By using the TGA thermogravimetric test method, the change of ligand density in the CsPbBr3 quantum dots prepared in Examples 1-3 was analyzed, as Figure 7 shown.

[0106] It can be Figure 7 seen that: when the post-treatment of the quantum dot solution is carried out by using the mixed solvent of the present invention, the more the proportion of tert-butanol, the more obvious the stripping effect on the DBSA ligand of the CsPbBr3 quantum dots.

[0107] Based on Figure 6 c and Figure 7 analysis, we can draw the following conclusion: although increasing the proportion of tert-butanol helps to improve the ligand stripping effect, excessive use may damage the crystal integrity of the quantum dots. Therefore, the inventor suggests that the volume ratio of tert-butanol to methyl acetate be further controlled between 1:(0.6-1.5) to obtain the best treatment effect.

[0108] The high-resolution transmission electron microscopy test was carried out on the CsPbBr3 quantum dots prepared in Examples 1-3 and Comparative Examples 1-4 after post-treatment by using a transmission electron microscope, and the test results are as Figure 8 , 9 shown.

[0109] Figure 8 shows the high-resolution transmission electron microscopy atomic image structure diagram of the CsPbBr3 quantum dots prepared in Examples 1-3 after post-treatment. It can be seen from the figure that when the volume ratio of the mixed solution of tert-butanol and methyl acetate is controlled within the range of 1:(0.6-1.5) during the post-treatment of the CsPbBr3 quantum dot solution passivated with DBSA ligand, the morphology and size of the quantum dots can self-assemble into nanorods.

[0110] Figure 9 Figure 1 shows the high-resolution transmission electron microscopy (HRTEM) atomic image structure diagrams of CsPbBr3 quantum dots prepared by post-treatment in Comparative Examples 1-4. For the quantum dots using DBSA ligand, in Comparative Examples 1-3, a mixed solution of tert-butanol and methyl acetate with volume ratios of 0:1, 1:4, and 4:1 was used for post-treatment respectively. It can be clearly seen from the figure that when the content of tert-butanol in the detergent is low, the change in solution polarity is small, and the morphology and structure of the quantum dots cannot be significantly changed; while when the content of tert-butanol is high, the solution polarity increases, resulting in the formation of overlapping nanorods in the quantum dots of Comparative Example 3. In Comparative Example 4, when the quantum dots prepared with OA and OLA ligands were post-treated with a mixed solvent of tert-butanol and methyl acetate with a volume ratio of 1:1, it can be seen from the figure that the quantum dots have agglomerated, indicating that their colloidal stability has significantly decreased. This shows that when too much tert-butanol is used, the excessive polarity easily leads to a phase change in the quantum dot solution during the post-treatment process, while too little tert-butanol cannot effectively regulate the morphology and structure of the quantum dots. Therefore, an appropriate polarity of the post-treatment solution is the key to changing its morphology and structure.

[0111] To analyze the effect of post-treatment on the photoluminescence quantum yield (PLQY) of CsPbBr3 quantum dots prepared in Examples 1-3 and Comparative Examples 1-4, the inventors conducted the following tests:

[0112] Take 10 mg of the prepared CsPbBr3 quantum dot powder and pour it into a cuvette, then add 4 mL of n-hexane and gently shake to promote its dissolution. Then place the cuvette in a photoluminescence spectrometer EI-FLS1000 for PL testing. Select the PL test module to obtain the PL emission intensity, and use an integrating sphere to measure the PLQY, and combine the test software to statistically analyze the PLQY value. The test results are shown in Table 1, Figure 10 、 11 as shown.

[0113] Table 1 Performance test results

[0114]

[0115]

[0116] It can be Figure 10 seen that the CsPbBr3 quantum dots in Examples 1-3 exhibited a PLQY higher than 80%; among them, Example 2 showed a PLQY close to 93%, indicating that Example 2 exhibited the best optical performance.

[0117] It can be Figure 11It can be seen that the PLQY values of Comparative Example 1 and Comparative Example 2 are close to 90%. For quantum dots containing DBSA ligands, appropriate ligand stripping does not change their optical properties; in Comparative Example 3, as the polarity of the post-treatment solvent increases, its optical performance gradually decreases; in Comparative Example 4, the optical properties of the quantum dots are relatively low, indicating that the washing effect of the quantum dots passivated by oleic acid and oleylamine ligands is poor during post-treatment.

[0118] Taking Examples 1 to 3 and Comparative Examples 1 to 2 as examples, LED devices were prepared and corresponding electrical performance tests were carried out. The preparation method includes the following steps:

[0119] Spin-coat the PEDOT:PSS (poly(3,4-ethylenedioxythiophene) / polystyrene sulfonate) solution onto an ITO (indium tin oxide) glass substrate (4000 r / min, 60 s), and heat-treat it at 140 °C for 15 min to form a PEDOT:PSS electron transport layer; then, dissolve the CsPbBr3 quantum dot powder prepared in each example in n-hexane (concentration of 5 mg / mL), and then spin-coat the quantum dot solution onto the above PEDOT:PSS layer at a speed of 2000 r / min for 60 s. After spin-coating, heat-treat it at 120 °C for 15 min. Finally, deposit TPBI and Al electrodes using a thermal evaporation system; under a vacuum of 2×10 -5 First, deposit 2 nm thick TPBI (1,3,5-tris(1-phenyl-1H-benzoimidazol-2-yl)benzene) as a hole transport layer at a rate of , and then deposit the Al electrode at a rate of to obtain the LED device, as shown in Figure 12 .

[0120] Analyze the LED devices prepared in Examples 1 to 3 and Comparative Examples 1 to 2 through an LED tester, and the change diagram of the current density under different voltage conditions. The results are as shown in Figure 13 、 14 .

[0121] It can be seen from Figure 13 that the LED devices of Examples 1 to 3 have a high current density, indicating that regulating the polarity of the post-treatment solvent effectively improves their electron transport efficiency.

[0122] It can be seen from Figure 14 that the current density of the device of Example 2 is higher than that of Comparative Example 1 and Comparative Example 2, indicating that when the DBSA ligand density is relatively high, the electron transport efficiency of its LED device is relatively low, and with the effective stripping of the ligand, the electron transport efficiency can be improved.

[0123] Test the external quantum dot efficiency of the LED devices prepared in Examples 1 to 3 and Comparative Examples 1 to 2 through a fluorescence quantum efficiency measurement instrument. The test results are asFigure 15 as shown

[0124] It can be seen from Figure 15 that the EQE values of the LED devices in Examples 1 to 3 generally exceed 8%, and the EQE value of the device in Example 2 is as high as 9.6%, which is nearly three times higher than that of Comparative Example 1 in the prior art.

[0125] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for regulating the morphological structure of perovskite quantum dot materials, characterized in that, It includes the following steps: S1. After mixing a cesium source, a lead source, octadecene, and dodecylbenzenesulfonic acid, heat and dissolve them under the protection of an inert gas to obtain a precursor solution containing the cesium source and the lead source; S2. Dissolve dioctadecylammonium bromide in 1,3,5-trimethylbenzene to obtain a precursor solution containing a bromine source; S3. After preheating the precursor solution containing the cesium source and the lead source in step S1, inject and mix it with the precursor solution containing the bromine source in step S2, and then cool to obtain a quantum dot solution; S4. Centrifuge and separate the quantum dot solution in step S3, add a post-treatment solvent to the supernatant, centrifuge to collect the precipitate, and dry it to obtain CsPbBr3 quantum dots; The post-treatment solvent is a mixed solvent of tert-butanol and methyl acetate in any volume ratio.

2. The method for regulating the morphology and structure of perovskite quantum dot materials according to claim 1, characterized in that, The volume ratio of the tert-butanol to the methyl acetate is 1:(0.6 - 1.5).

3. The method for regulating the morphological structure of perovskite quantum dot materials according to claim 1, characterized in that, In step S1, the mass-volume ratio of the cesium source, the lead source, octadecene, and dodecylbenzenesulfonic acid is (0.06 - 0.15) g:0.076 g:(5 - 25) ml:(0.5 - 1.5) ml.

4. The method for regulating the morphological structure of perovskite quantum dot materials according to claim 3, characterized in that, In step S1, the dissolution temperature is 100 - 120 °C and the time is 1 - 1.5 h.

5. The method for regulating the morphology and structure of perovskite quantum dot materials according to claim 1, characterized in that, In step S2, the mass-volume ratio of the dioctadecylammonium bromide to the 1,3,5-trimethylbenzene is 0.4367 g:(0.5 - 1.5) ml.

6. The method for regulating the morphology and structure of perovskite quantum dot materials according to claim 1, wherein, In step S3, the preheating temperature is 150 - 160 °C; the mixing time is 2 - 10 min.

7. The method for regulating the morphology and structure of perovskite quantum dot materials according to claim 1, characterized in that, In step S4, the centrifugation speed is 7500 - 8500 rpm and the time is 5 - 10 min.

8. The method for regulating the morphology and structure of perovskite quantum dot materials according to claim 7, characterized in that, In step S4, the drying temperature is 40 - 60 °C and the time is 12 - 24 h.

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