Method for regulating morphology and structure of perovskite quantum dot material

Abstract

The application provides a method for regulating morphology and structure of 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 dodecylbenzenesulfonic acid, and then heating and dissolving under the protection of inert gas to obtain a precursor solution containing the cesium source and the lead source; S2, dissolving double-octadecylammonium bromide in 1,3,5-trimethylbenzene to obtain a precursor solution containing a bromine source; S3, mixing the two kinds of precursor solutions and cooling to obtain a quantum dot solution; and S4, centrifugally separating the crude solution, adding a mixed solvent of tertiary butyl alcohol and methyl acetate with an arbitrary volume ratio into supernatant, and again centrifugally collecting the precipitate, so as to prepare CsPbBr3 quantum dots after drying.The method effectively regulates the morphology and structure of the quantum dots from dots to nanorods, and meanwhile, good colloidal structure stability is exhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of perovskite nanocrystal preparation, and particularly to a method for regulating morphology and structure of perovskite quantum dot material. BACKGROUND

[0002] Semiconductor nanocrystals (NCs), especially colloidal quantum dots (QDs), have attracted extensive attention due to their tight correlation between size and shape with optoelectronic properties. The size of QDs is usually between 2-20 nm, and the quantum confinement effect brought by this tiny size endows them with higher color purity, luminescence intensity and excellent stability, making them an ideal choice for optoelectronic applications. Perovskite quantum dots (PQDs) as a special class of QD materials, due to their low cost, excellent stability, high photoluminescence and high carrier mobility, etc., have shown great application potential in visible light communication, solar cells, photodetectors, biological imaging and LED devices, etc.

[0003] Since the first report in 2014, researchers have been committed to regulating the morphology and size of PQDs to optimize their optoelectronic properties. These regulation techniques of PQD materials can be summarized into two kinds, the first is during the synthesis process, this process is mainly achieved by two ways: one is to regulate during the synthesis process, the other is to post-treat the synthesized PQDs. Hot-injection method is one of the commonly used synthesis regulation means, this method usually involves high temperature and fast nucleation kinetics, and needs to introduce different ligands to control the growth of quantum dots. These ligands not only play the role of stabilizer, increase the stability of PQD colloid, but also passivate surface defects, improve the luminescence efficiency. However, too much ligand will cause the problem of decreased electron transport efficiency.

[0004] To solve this problem, post-processing technology becomes crucial. The post-processing process generally refers to: by adding a solvent of appropriate polarity (such as ethyl acetate or methyl acetate) to the PQD colloid, to remove excess surface ligands, promote particle combination or crystal phase reconstruction, etc., so as to improve the applicability of PQD materials in optoelectronic devices. For example, the PQD colloid solution synthesized by using the commonly used oleic acid (OA) and oleylamine (OLA) ligands, although the luminescent performance is improved, but in the post-processing process, due to the weak binding force of oleic acid and oleylamine with quantum dots, it is easy to be affected by the solution polarity and environmental factors, leading to the desorption of PQD ligands or phase transition and affecting the stability of the colloid. In addition, after the PQD synthesized by such oleic acid and oleylamine ligands undergoes 2-3 times of post-processing process, not only the morphology size of the quantum dots cannot be effectively controlled, but also the colloidal stability will be seriously decreased. Researchers found that using strong binding force of dodecylbenzenesulfonic acid (DBSA) instead of traditional oleic acid (OA) and oleylamine (OLA) ligands can significantly enhance the colloidal stability and optical performance of PQD after multiple post-processing. However, this process usually only removes free ligands, but cannot effectively remove part of the DBSA ligands combined with PQD, and even after 6 times of washing, the light-emitting efficiency of the prepared LED device is extremely low. In summary, in the post-processing stage, the removal of excess ligands can improve the carrier transport efficiency of PQD to a certain extent, but the removal of too much ligand will affect the colloidal stability and luminescent properties.

[0005] Therefore, it is urgent to develop a new method for regulating the morphology of quantum dots to obtain PQD materials with excellent optoelectronic performance, so as to balance the colloidal stability and electrical performance. SUMMARY

[0006] Therefore, the present application provides a method for regulating the morphology of perovskite quantum dot materials to promote the stability of CsPbBr3 in air environment and the photoelectron transport performance thereof.

[0007] The present application provides a method for regulating the morphology of perovskite quantum dot materials, comprising the following steps:

[0008] S1, mixing a cesium source, a lead source, octadecene (ODE) and dodecylbenzenesulfonic acid (DBSA), and then heating and dissolving under the protection of inert gas to obtain a precursor solution containing cesium source and lead source;

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

[0010] S3, preheating the precursor solution containing cesium source and lead source of step S1, then injecting the precursor solution containing bromine source of step S2 for mixing, and then cooling to obtain a quantum dot solution;

[0011] S4, centrifugal separation of the quantum dot solution of step S3, adding a post-processing solvent to the supernatant, collecting the precipitate by centrifugation, and drying to obtain CsPbBr3 quantum dots;

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

[0013] In one or some possible embodiments, the volume ratio of the tert-butyl alcohol to the 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, the 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 dissolving temperature is 100-120℃, and the time is 1-1.5 h.

[0017] In one or some possible embodiments, 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.

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

[0019] In one or some possible embodiments, in step S4, the centrifugal 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℃, and the time is 12-24 h.

[0021] The method for regulating the morphology and structure of perovskite quantum dot material provided by the application has the following beneficial effects relative to the prior art:

[0022] (1) The post-processing solvent (methyl acetate and tert-butyl alcohol) used in the application has a stronger washing effect on the surface ligand (DBSA) of cesium-lead-bromine quantum dots, exhibits good colloidal structure stability, and effectively regulates the morphology and structure of the quantum dots from perovskite quantum dots to perovskite nanorods.

[0023] (2) The CsPbBr3 quantum dots prepared by the application have been significantly improved in optical performance (photoluminescence quantum yield, PLQY) and electrical performance (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 by the quantum dots is as high as 9.6%, which is nearly 3 times higher than the quantum dot film LED device using DBSA ligand passivation in the prior art, and has great advantages in electron transport efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0025] Figure 1 A schematic diagram of the post-treatment process of the quantum dot solution of the application;

[0026] Figure 2 A post-treatment physical diagram of the CsPbBr3 quantum dots of Examples 1-3 and Comparative Examples 1-3 of the application;

[0027] Figure 3 A post-treatment physical diagram of the CsPbBr3 quantum dots of Comparative Example 4 of the application;

[0028] Figure 4 A post-treatment physical diagram of the CsPbBr3 quantum dots of Comparative Example 5 of the application;

[0029] Figure 5 An XRD test diagram of the CsPbBr3 quantum dots prepared by Examples 1-3 of the application;

[0030] Figure 6 An XRD test diagram of the CsPbBr3 quantum dots prepared by Example 2 and Comparative Examples 1-4 of the application;

[0031] Figure 7 A ligand density change diagram of the CsPbBr3 quantum dots prepared by Examples 1-3 of the application;

[0032] Figure 8 A high-resolution transmission electron microscope atomic image structure diagram of the CsPbBr3 quantum dots prepared by Examples 1-3 of the application;

[0033] Figure 9 A high-resolution transmission electron microscope atomic image structure diagram of the CsPbBr3 quantum dots prepared by Comparative Examples 1-4 of the application;

[0034] Figure 10 PLQY test chart of CsPbBr3 quantum dots prepared for the present application examples 1-3;

[0035] Figure 11 PLQY test chart of CsPbBr3 quantum dots prepared for the present application example 2 and comparative examples 1-4;

[0036] Figure 12 Schematic diagram of LED device prepared for the present application;

[0037] Figure 13 Current density-voltage relationship chart of LED device prepared for the present application examples 1-3;

[0038] Figure 14 Current density-voltage relationship chart of LED device prepared for the present application example 2 and comparative examples 1, 2;

[0039] Figure 15 External quantum efficiency test result chart of LED device prepared for the present application examples 1-3 and comparative examples 1-2. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0041] In order to effectively control the morphology of quantum dots in the post-processing process, the prior art proposes a method of removing surface ligands and promoting particle combination or crystal phase reconstruction by changing the polarity of the post-processing solution. The inventors found in the research process that: because PQD has ionic characteristics, it shows 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 the post-processing solvent suitable for PQD colloidal solution is relatively limited. Although the commonly used medium polarity solvents such as methyl acetate or ethyl acetate can partially remove the surface ligands, the effect is not ideal for DBSA ligand passivated PQD. If more polar alcohol solvents such as methanol and ethanol are used, the structure of the quantum dots may be damaged, affecting their stability. Since the prior art does not meet the expectations of the inventors, the inventors have made the present application through further exploration and research.

[0042] This invention employs a hybrid strategy, using a mixture of more polar tert-butanol and moderately polar methyl acetate or ethyl acetate as the post-treatment solvent for quantum dot solutions. Compared to 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 discovered that by adjusting the ratio of these two solvents, the overall polarity of the post-treatment solvent can be precisely controlled, thereby achieving effective regulation of the morphology and size of DBSA-passivated PQDs. This method not only solves the problem of difficulty in controlling the morphology and structure of perovskite nanocrystal colloids during post-treatment but also enables quantum dots to self-assemble into nanorods, further optimizing their photoelectric properties.

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

[0044] S1. Cesium source, lead source, octadecene and dodecylbenzenesulfonic acid are mixed and then heated to dissolve under the protection of an inert gas to obtain a precursor solution containing cesium source and 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 cesium and lead sources from step S1, inject it into the precursor solution containing bromine sources from step S2 and mix. Then cool to obtain a quantum dot solution.

[0047] S4, see appendix Figure 1 The quantum dot solution from step S3 was centrifuged, and a post-treatment solvent was added to the supernatant. After centrifugation to collect the precipitate, it was dried to obtain CsPbBr3 quantum dots.

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

[0049] By adding mixed solvents in different proportions during post-processing, this invention can effectively control the morphology and size of quantum dots, enabling perovskite quantum dots to self-assemble from nanocrystals into nanorods. This control process is attributed to the kinetics of ligand binding to the PQD surface: during ligand detachment, PQD crystals preferentially grow towards facets with lower binding energies. 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 description is based on specific embodiments. Unless otherwise specified, the materials and equipment involved in the embodiments are all commercially available conventional products.

[0051] Example 1

[0052] S1, 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 were mixed, heated to 100°C under the protection of nitrogen, stirred for 1 h to dissolve, to exclude water oxygen, to obtain a precursor solution containing cesium source and lead source;

[0053] S2, 0.4367 g of DDOAB was dissolved in 1 ml of 1,3,5-trimethylbenzene, and shaken to dissolve, to obtain a precursor solution containing bromine source;

[0054] S3, the precursor solution containing cesium source and lead source of step S1 was preheated to 155°C, 1 ml of the precursor solution containing bromine source of step S2 was injected, mixed for 2 min, then cooled to room temperature in an ice water bath, to obtain a quantum dot solution;

[0055] S4, the quantum dot solution of step S3 was centrifuged at a speed of 7800 rpm for 5 min, the supernatant was separated and collected to remove the incomplete precipitate, a post-processing solvent (volume ratio of 2:3) was added to the supernatant, centrifuged at a speed of 7500 rpm for 8 min, and the precipitate was separated and collected, the process was repeated twice, and finally the precipitate was dried at 50°C for 18 h, to obtain CsPbBr3 quantum dots;

[0056] The post-processing solvent is a mixed solvent of tert-butyl alcohol and methyl acetate with a volume ratio of 2:3.

[0057] Example 2

[0058] S1, 0.1 g of Cs2CO3, 0.076 g of Pb(Ac)2, 10 ml of ODE and 1 ml of DBSA were mixed, heated to 100°C under the protection of nitrogen, stirred for 1 h to dissolve, to exclude water oxygen, to obtain a precursor solution containing cesium source and lead source;

[0059] S2, 0.4367 g of DDOAB was dissolved in 1 ml of 1,3,5-trimethylbenzene, and shaken to dissolve, to obtain a precursor solution containing bromine source;

[0060] S3, the precursor solution containing cesium source and lead source of step S1 was preheated to 155°C, 1 ml of the precursor solution containing bromine source of step S2 was injected, mixed for 2 min, then cooled to room temperature in an ice water bath, to obtain a quantum dot solution;

[0061] S4, the quantum dot solution of step S3 was centrifuged at a speed of 7800 rpm for 5 min, the supernatant was separated and collected to remove the incomplete precipitate, a post-processing solvent (volume ratio of 2:3) was added to the supernatant, centrifuged at a speed of 7500 rpm for 8 min, and the precipitate was separated and collected, the process was repeated twice, and finally the precipitate was dried at 50°C for 18 h, to obtain CsPbBr3 quantum dots;

[0062] The post-processing solvent is a mixture of tert-butyl alcohol and methyl acetate in a volume ratio of 1:1.

[0063] Example 3

[0064] S1, 0.1 g of Cs2CO3, 0.076 g of Pb(Ac)2, 10 ml of ODE and 1 ml of DBSA were mixed, and then heated to 100°C under the protection of nitrogen, stirred for 1 h to dissolve, to exclude water oxygen, to obtain a precursor solution containing cesium source and lead source;

[0065] S2, 0.4367 g of DDOAB was dissolved in 1 ml of 1,3,5-trimethylbenzene, and shaken to dissolve, to obtain a precursor solution containing bromine source;

[0066] S3, the precursor solution containing cesium source and lead source in step S1 was preheated to 155°C, 1 ml of the precursor solution containing bromine source in step S2 was injected, mixed for 2 min, and then cooled to room temperature in an ice water bath, to obtain a quantum dot solution;

[0067] S4, the quantum dot solution in step S3 was centrifuged at a speed of 7800 rpm for 5 min, the supernatant was collected to remove the precipitate, post-processing solvent (volume ratio of 3:2) was added to the supernatant, and then centrifuged at a speed of 7500 rpm for 8 min, the precipitate was collected, the process was repeated for 2 times, and finally the precipitate was dried at 50°C for 18 h, to obtain CsPbBr3 quantum dots;

[0068] The post-processing solvent is a mixture of tert-butyl alcohol and methyl acetate in a volume ratio of 3:2.

[0069] Example 4

[0070] S1, 0.06 g of Cs2CO3, 0.076 g of Pb(Ac)2, 5 ml of ODE and 0.5 ml of DBSA were mixed, and then heated to 100°C under the protection of nitrogen, stirred for 1 h to dissolve, to exclude water oxygen, to obtain a precursor solution containing cesium source and lead source;

[0071] S2, 0.4367 g of DDOAB was dissolved in 0.5 ml of 1,3,5-trimethylbenzene, and shaken to dissolve, to obtain a precursor solution containing bromine source;

[0072] S3, the precursor solution containing cesium source and lead source in step S1 was preheated to 150°C, 1 ml of the precursor solution containing bromine source in step S2 was injected, mixed for 5 min, and then cooled to room temperature in an ice water bath, to obtain a quantum dot solution;

[0073] S4, centrifuging the quantum dot solution of step S3 at a speed of 8500 rpm for 10 min, separating and collecting the supernatant to remove the incomplete precipitation of the reaction, adding a post-processing solvent (volume ratio of 2:3) to the supernatant, centrifuging at a speed of 7500 rpm for 5 min, and then separating and collecting the precipitate, which can be repeated 2-3 times, and finally drying the precipitate at 50°C for 24 h to obtain the CsPbBr3 quantum dots;

[0074] The post-processing solvent is a mixed solvent of tert-butyl alcohol and methyl acetate with a volume ratio of 2:3.

[0075] Example 5

[0076] S1, mixing 0.1 g of Cs2CO3, 0.076 g of Pb(Ac)2, 15 ml of ODE and 1 ml of DBSA, heating to 110°C under the protection of nitrogen, stirring for 1.2 h to dissolve, and removing water and oxygen to obtain a precursor solution containing cesium and lead sources;

[0077] S2, dissolving 0.4367 g of DDOAB in 1 ml of 1,3,5-trimethylbenzene, and oscillating to dissolve to obtain a precursor solution containing a bromine source;

[0078] S3, preheating the precursor solution containing cesium and lead sources of step S1 to 155°C, injecting 1 ml of the precursor solution containing the bromine source of step S2, mixing and reacting for 8 min, and then cooling to room temperature in an ice water bath to obtain a quantum dot solution;

[0079] S4, centrifuging the quantum dot solution of step S3 at a speed of 7500 rpm for 5 min, separating and collecting the supernatant to remove the incomplete precipitation of the reaction, adding a post-processing solvent (volume ratio of 1:1) to the supernatant, centrifuging at a speed of 7500 rpm for 5 min, and then separating and collecting the precipitate, which can be repeated 2-3 times, and finally drying the precipitate at 60°C for 12 h to obtain the CsPbBr3 quantum dots;

[0080] The post-processing solvent is a mixed solvent of tert-butyl alcohol and methyl acetate with a volume ratio of 1:1.

[0081] Example 6

[0082] S1, mixing 0.15 g of Cs2CO3, 0.076 g of Pb(Ac)2, 25 ml of ODE and 1.5 ml of DBSA, heating to 120°C under the protection of nitrogen, stirring for 1.5 h to dissolve, and removing water and oxygen to obtain a precursor solution containing cesium and lead sources;

[0083] S2, dissolving 0.4367 g of DDOAB in 1.5 ml of 1,3,5-trimethylbenzene, and oscillating to dissolve to obtain a precursor solution containing a bromine source;

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

[0085] S4, the quantum dot solution in step S3 is centrifuged at a speed of 8500 rpm for 10 min, the supernatant is collected to remove the precipitate of incomplete reaction, and a post-processing solvent (volume ratio of 3:2) is added to the supernatant, and after centrifugation at a speed of 7500 rpm for 5 min, the precipitate is collected, and the process can be repeated 2-3 times, and finally the precipitate is dried at 55°C for 14h;

[0086] The post-processing solvent is a mixed solvent of tert-butyl alcohol 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 is used as the post-processing solvent, and the other steps remain unchanged.

[0089] Comparative Example 2

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

[0091] Comparative Example 3

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

[0093] Comparative Example 4

[0094] The difference from Example 2 is that in step S1, OA and OLA are used instead of DBSA, and the other steps remain unchanged.

[0095] Comparative Example 5

[0096] The difference from Example 2 is that the post-processing solvent is isopropyl alcohol, and the other steps remain unchanged.

[0097] The physical pictures of the quantum dot solutions prepared in Examples 1-3 and Comparative Examples 1-5 after the post-processing process are recorded as shown in Figures 2-4 .

[0098] Figure 2The middle three groups of real pictures respectively show the states before, during and after post-processing, and each group of pictures contains 6 centrifugal tubes, which correspond to the real pictures of the quantum dot solutions prepared by Comparative Example 1, Comparative Example 2, Example 1, Example 2, Example 3 and Comparative Example 3 at different processing stages from left to right. As can be seen from the figure: the quantum dot solutions prepared by the examples and comparative examples can maintain a stable state before post-processing, and after completing the post-processing, the quantum dot solutions prepared by Comparative Examples 1-2 can still maintain stability, while the quantum dot solution prepared by Comparative Example 3 is obviously yellow, indicating that the stability of the quantum dot solution is destroyed by the polar solvent, thereby causing the quantum dot solution to undergo phase transition, so it can be inferred that the use of tert-butyl alcohol alone for post-processing is more likely to destroy the stability of the quantum dots. At the same time, the quantum dot solutions of Examples 1-3 samples can still maintain good solution stability before and after processing, indicating that the post-processing of the quantum dot solution by the method of the application will not cause structural phase transition.

[0099] Figure 3 The left to right corresponds to the real pictures of the quantum dot solution prepared by Comparative Example 4 before and after post-processing. As can be seen from the figure: after post-processing with a mixed solvent of tert-butyl alcohol and methyl acetate in a volume ratio of 1:1, the color of the quantum dot solution becomes yellow, indicating that the quantum dot solution has undergone phase transition. It can be inferred from this that the combination effect of oleic acid and oleylamine on cesium lead bromide quantum dots is not strong, so the post-processing effect using the mixed solvent of the application is not ideal, which shows that the regulation method of the application has certain pertinence and has a significant advantage for using DBSA ligand.

[0100] Figure 4 The left to right corresponds to the real pictures of the quantum dot solution prepared by Comparative Example 5 before and after post-processing. As can be seen from the figure: after post-processing with isopropanol, the color of the quantum dot solution becomes yellow, indicating that the result has undergone phase transition and precipitation. It shows that using only a polar isopropanol solution for post-processing process will destroy the stability of the quantum dot solution.

[0101] XRD tests were performed on the CsPbBr3 quantum dots prepared in Examples 1-3 to observe their crystal structures, and the test results are shown in Figure 5 .

[0102] As can be seen from Figure 5 : when the ratio of post-processing solvents methyl acetate and tert-butyl alcohol is in the range of 2:3 to 3:2, the samples of Examples 1-3 show (100), (110), (111), (200), (210), (211), (202), (103) and other crystal face characteristic XRD peaks, proving that post-processing with mixed solvents in this interval will not affect the phase structure of CsPbBr3 quantum dots.

[0103] X-ray diffraction was used to perform XRD tests on the CsPbBr3 quantum dots prepared in comparative examples 1–4 to observe their crystal structure. The test results are as follows: Figure 6 As shown.

[0104] Depend on Figure 6 It is understood that when using the mixed solvent of the present invention for post-treatment of quantum dot solutions, if the proportion of tert-butanol is low, such as... Figure 6 a and Figure 6 As shown in b, its XRD phase structure remained unchanged, indicating that a small amount of ligand exfoliation did not alter its crystal structure; with the increase of the proportion of tert-butanol added, as... Figure 6 As shown in c, its XRD phase structure has changed, indicating that excessive tert-butanol treatment can easily lead to the destruction of the crystal structure. Figure 6 The XRD pattern of d shows that there are impurity peaks in the CsPbBr3 quantum dots prepared in Comparative Example 4, indicating that its crystal structure is beginning to destabilize and is prone to phase transition.

[0105] The changes in ligand density in the CsPbBr3 quantum dots prepared in Examples 1-3 were analyzed using thermogravimetric analysis (TGA). Figure 7 As shown.

[0106] Depend on Figure 7 It is known that when using the mixed solvent of the present invention to post-treat the quantum dot solution, the higher the proportion of tert-butanol, the more obvious the stripping effect on the DBSA ligand of CsPbBr3 quantum dots.

[0107] based on Figure 6 c and Figure 7 Based on the analysis, we can draw the following conclusions: Although increasing the proportion of tert-butanol helps to improve the exfoliation effect of ligands, excessive use may damage the crystal integrity of quantum dots. Therefore, the inventors suggest that the volume ratio of tert-butanol to methyl acetate should be further controlled between 1:(0.6 to 1.5) to obtain the best treatment effect.

[0108] High-resolution transmission electron microscopy (TEM) was used to examine the CsPbBr3 quantum dots prepared after post-processing in Examples 1-3 and Comparative Examples 1-4. The results are as follows: Figure 8 , 9 As shown.

[0109] Figure 8 High-resolution transmission electron microscopy (TEM) atomic structure images of CsPbBr3 quantum dots prepared by post-treatment in Examples 1-3 are shown. As can be seen from the figures, when the volume ratio of tert-butanol and methyl acetate mixed in the CsPbBr3 quantum dot solution passivated by DBSA ligand is controlled within the range of 1:(0.6-1.5) during post-treatment, the quantum dot morphology and size can self-assemble into nanorods.

[0110] Figure 9 High-resolution transmission electron microscopy (TEM) atomic structure images of CsPbBr3 quantum dots prepared by post-treatment in Comparative Examples 1–4 are shown. For quantum dots using DBSA ligands, Comparative Examples 1–3 were post-treated with mixed solutions of tert-butanol and methyl acetate at volume ratios of 0:1, 1:4, and 4:1, respectively. The images clearly show that when the tert-butanol content in the detergent is low, the solution polarity does not change significantly, and the morphology of the quantum dots is not significantly altered. However, when the tert-butanol content is high, the solution polarity increases, leading to the formation of overlapping nanorods in Comparative Example 3. In Comparative Example 4, the quantum dots prepared using OA and OLA ligands showed aggregation when post-treated with a mixed solvent of tert-butanol and methyl acetate at a volume ratio of 1:1, indicating a significant decrease in their colloidal stability. This indicates that using too much tert-butanol can lead to excessive polarity and cause a phase transition in the quantum dot solution during post-processing. Conversely, using too little tert-butanol will fail to effectively control the morphology and structure of the quantum dots. Therefore, appropriate polarity of the post-processing solution is key to changing its morphology and structure.

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

[0112] 10 mg of the prepared CsPbBr3 quantum dot powder was poured into a cuvette, and 4 mL of n-hexane was added. The mixture was gently shaken to promote dissolution. The cuvette was then placed in an EI-FLS1000 photoluminescence spectrometer for PL measurement. The PL luminescence intensity was obtained by selecting the PL measurement module, and PLQY was measured using an integrating sphere. The PLQY values ​​were then statistically analyzed using the testing software. The test results are shown in Table 1. Figure 10 , 11 As shown.

[0113] Table 1 Performance Test Results

[0114]

[0115]

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

[0117] Depend on Figure 11It can be seen that the PLQY values of Comparative Example 1 and Comparative Example 2 are close to 90%, and the appropriate amount of ligand stripping does not change the optical properties of the quantum dots containing the DBSA ligand; in Comparative Example 3, the optical properties gradually decrease with the increase of the polarity of the post-processing solvent; 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 the oleic acid / oleylamine ligand is not good in the post-processing.

[0118] For Examples 1-3 and Comparative Examples 1-2, LED devices were prepared and the corresponding electrical performance tests were performed, and the preparation method included the following steps:

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

[0120] The LED devices prepared in Examples 1-3 and Comparative Examples 1-2 were analyzed by an LED tester, and the current density change graph under different voltage conditions is shown in Figure 13 , 14 .

[0121] It can be seen from Figure 13 that the LED devices of Examples 1-3 have a higher current density, indicating that adjusting the polarity of the post-processing solvent effectively improves the 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 Examples 1 and 2, indicating that when the DBSA ligand density is higher, the electron transport efficiency of the LED device is lower, and the electron transport efficiency can be improved with effective stripping of the ligand.

[0123] The external quantum dot efficiency of the LED devices prepared in Examples 1-3 and Comparative Examples 1-2 was tested by a fluorescence quantum efficiency measuring instrument, and the test results are shown in​Figure 15 as shown.

[0124] From Figure 15 It can be seen that the LED devices of Examples 1 to 3 generally exceed an EQE value of 8%, with the EQE value in the device of Example 2 being as high as 9.6%, which is nearly 3 times greater than the comparative Example 1 of the prior art.

[0125] The above description is merely that of the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall fall within the scope of the present application.

Claims

1.A method for regulating morphology of perovskite quantum dot material, characterized in that, The method comprises the following steps: S1, mixing a cesium source, a lead source, octadecene and dodecylbenzenesulfonic acid, and then heating and dissolving under the protection of inert gas to obtain a precursor solution containing the cesium source and the lead source; S2, dissolving dioctadecylammonium bromide in 1, 3, 5-trimethylbenzene to obtain a precursor solution containing a bromine source; S3, preheating the precursor solution containing the cesium source and the lead source in step S1 to 150-160 DEG C, then injecting the precursor solution containing the bromine source in step S2, mixing for 2-10 min, and then cooling to obtain a quantum dot solution; S4, centrifuging the quantum dot solution in step S3, adding a post-treatment solvent to the supernatant, centrifuging to collect the precipitate, and then drying to obtain CsPbBr3 nanorods; The post-treatment solvent is a mixed solvent of tert-butyl alcohol and methyl acetate, and the volume ratio of tert-butyl alcohol to methyl acetate is 1: (0.6-1.5). 2.The method of claim 1, wherein the method comprises: adjusting a pH value of the solution to a range of 1.5-2.5; and adjusting a temperature of the solution to a range of 60-80 ℃. 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. 3.The method of claim 1, wherein the method comprises: adjusting a pH value of the solution to be between 1 and 3; and adjusting a temperature of the solution to be between 60 ℃ and 80 ℃. In step S1, the dissolving temperature is 100-120 DEG C, and the time is 1-1.5 h. 4.The method of claim 1, wherein the method comprises: adjusting a pH value of a solution containing the perovskite quantum dots; and adjusting a concentration of a ligand of the perovskite quantum dots. In step S2, the mass-volume ratio of dioctadecylammonium bromide to 1, 3, 5-trimethylbenzene is 0.4367 g: (0.5-1.5) ml. 5.The method of claim 1, wherein the method comprises: adjusting a pH value of a solution containing the perovskite quantum dot material to a first pH value; and adjusting the pH value of the solution to a second pH value. In step S4, the centrifugal speed is 7500-8500 rpm, and the time is 5-10 min. 6.The method of claim 5, wherein the method further comprises: adjusting the concentration of the halide ions in the solution to control the morphology of the perovskite quantum dots. In step S4, the drying temperature is 40-60 DEG C, and the time is 12-24 h.

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