High-Quality CdS-Based Anionic And Cationic Alloy Blue Quantum Dots And Their Application In Light-Emitting Diodes

Quantum dots（QDs）are considered to be one of the rising star materials in the field of display lighting because of their continuously tunable emission spectra,high fluorescence quantum yield,excellent color purity,good photochemical stability,and solution processability.With the continuous exploration of quantum dot synthesis technology,surface ligand modification and device structure,the device performance of red and green quantum dot light-emitting diodes（QLED）has been developed rapidly and basically meets the demand of display lighting applications,however,the performance of blue QLED is far behind that of red and green QLEDs,which is one of the bottlenecks limiting the application of QLED.The main reason for limiting the performance of blue QLED devices is the deep valence band energy level of blue QDs,which leads to a large injection barrier between them and the hole transport layer,resulting in low hole injection efficiency and unbalanced carrier injection.Cd S QDs as a wide bandgap direct bandgap semiconductor material,can achieve fluorescence emission in the whole blue region by size tuning,and at the same time,the construction of alloyed quantum dot system is beneficial for quantum dots energy band position tuning,suppression of oscillation complex and scintillation phenomena,and construction of core-shell structure quantum dots with thick shell layer.Based on this,this thesis adopts the strategy of building anion/cation alloying from the structure of quantum dots to design and synthesize high-quality blue Cd S-based alloyed quantum dot systems and construct QLED devices,which provides new ideas for the development of blue QLED.（1）Preparation of CdZnS/ZnS quantum dots and their light-emitting diode study:in this chapter,we explore the cationic alloyed CdZnS system,design and synthesize high-quality blue CdZnS/ZnS core-shell quantum dots by material component design and shell layer growth activity regulation strategy,and construct QLED devices based on the quantum dots.Firstly,we optimized the feeding ratio of Cd:Zn:S to produce high-quality alloyed CdZnS nuclei,and clarified that the alloyed CdZnS nuclei were best matched when the feeding ratio of Cd:Zn:S was 2:16:3;subsequently,CdZnS/ZnS quantum dots with a fluorescence peak position at 472 nm and a half-peak width of 29 nm and a fluorescence quantum yield of more than 80%were successfully prepared using S-TOP as the sulfur source and Zn-OA as the zinc source.Further constructing QLED devices based on the quantum dots,the maximum brightness of the devices is 26850 cd/m²,the peak EQE is 16.26%,and the maximum current efficiency is 13.77 cd/A.（2）Preparation of CdSeS/ZnSeS/ZnS quantum dots and their light-emitting diode study:in this chapter,we explore the anion alloyed CdSeS system,and firstly through the control of anion components and activity,we prepare CdSeS nuclei with UV-visible absorption peak position tuned in the range of 420-460 nm,and the CdSeS nuclei with a Se:S ratio of 1:2were preferred to be the best match.Subsequently,CdSeS/4 ML ZnSe_0.4S_0.6/4 ML ZnS quantum dots with a fluorescence peak position at 470 nm,a half-peak width of 26 nm and a fluorescence quantum yield of more than 90%were successfully prepared by adjusting the Se,S ratio in the ZnSeS shell layer,ZnSeS layer thickness and ZnS layer thickness based on the shell layer component and thickness tuning strategy.Based on this high-quality quantum dot as the light-emitting layer,the QLED device was constructed by the solution method,and the maximum brightness of the device was 41,243cd/m²,the maximum EQE was 22.51%,and the maximum current efficiency was 19.03 cd/A,where EQE is the highest blue efficiency reported so far.The design and synthesis of this high quality blue CdSeS/ZnSeS/ZnS core-shell structure quantum dots provide a new material choice and research idea for blue QLED development.