Preparation Of Green CdZnSeS Gradient Alloy Core-shell Quantum Dots And Study On Their Performance Of Devices

Quantum dots(QDs),as a strong competitor for the next generation of display materials,have the advantages of continuously adjustable emission spectrum,high fluorescent quantum yield,high color purity,strong chemical stability,and solution processability.After decades of exploration by researchers,the synthesis technology of quantum dots has rapidly developed.The performance of quantum dot light-emitting diodes(QLEDs)based on quantum dots has also steadily improved and has now essentially met the application requirements for displays and lighting.Multicomponent alloy quantum dots are increasingly favored by researchers because their band positions can be easily modulated.Due to the lattice mismatch and energy level position difference of core-shell materials,binary CdSe-based quantum points lead to serious core-shell interface defects and band bending,which affect the performance of light-emitting devices.CdZnSeS quaternary alloy quantum dots have adjustable energy levels and lattice parameters,which can effectively improve core-shell interface defects and band bending.However,current methods for synthesizing quaternary alloy quantum dots primarily rely on adjusting the relative proportions of each element to control the composition structure,which is relatively simple and has limited tuning space for a specific color.Based on this,this article starts with the synthesis of quantum dots and introduces highly active surface ligands to change the precursor concentration and regulate the composition distribution of gradient alloy quantum dots,designing and synthesizing CdZnSeS/ZnSeS/ZnS gradient alloy core-shell quantum dots with gradient composition distribution structures,which provides a new idea for synthesizing CdZnSeS quaternary alloy quantum dot systems.The specific content is as follows:(1)Preparation of CdZnSeS/ZnSeS/ZnS quantum dots based on CdZnSeS gradient alloy crystal nuclei and study on the performance of its devices: In this chapter,this article explore the CdZnSeS quaternary quantum dot system and add the precursor 2-ethylhexanoic acid(EHA)as a surface ligand to change the differential reactivity of each element precursor,adjust the composition distribution of CdZnSeS quantum dots by changing the amount of EHA used,and successfully synthesize gradient alloy quantum dots with different degrees.Through the growth kinetics study of quantum dots,this article found that an appropriate amount of EHA can enhance the reactivity of Znprecursors,but excess EHA leads to an increase in the overall reaction system activity and surface defects of quantum dots.Subsequently,ZnSeS and ZnS shells were grown on these gradient alloy quantum dots,and QLED devices were constructed.Based on quantum dot characterization and device results,this article found that CdZnSeS gradient alloy quantum dots with cores coated with CdZnSeS/ZnSeS/ZnS shells using 2 m L EHA had the highest relative fluorescent quantum yield of 58%,and their devices had maximum brightness of 212828.52 cd/m~2,which were the best among the four types of quantum dots studied.(2)Shell regulation of CdZnSeS/ZnSeS/ZnS gradient alloy core-shell quantum dots and study on the performance of its devices: Based on the previous chapter’s research,this article selected CdZnSeS gradient alloy quantum dots with 2 m L EHA for this chapter’s quantum dot nuclei.This article changed the Seand S in the 6 m L ZnSeS shell layer and introduced a gradient alloy intermediate shell layer to achieve a gradient variation of Seand S elements in the ZnSeS shell layer.Based on the quantum dot characterization,this article found that the Se/S ratio of the 2 m L ZnSeS shell layer adjacent to the CdZnSeS nuclei was 2:1,while that of the 2 m L ZnSeS shell layer adjacent to the ZnS shell was 1:2.Then,this article added an intermediate shell layer with a Se/S ratio of 1:1 in the ZnSeS shell layer,successfully synthesizing CdZnSeS/ZnSeS/ZnS gradient alloy core-shell quantum dots with a fluorescent quantum yield of 93%.Compared to quantum dots without shell regulation,the valence band of these shell-regulated quantum dots was further raised,reducing the hole injection barrier and facilitating carrier injection balance.Finally,this article constructed QLED devices based on these quantum dots,and the maximum external quantum efficiency of the device reached 13.39%,the maximum current efficiency was 54.39 cd/A,and the maximum brightness was 412325 cd/m~2.