Preparation Of Multi-Ligand Modified CsPbBr₃ Perovskite Quantum Dots And LED Devices

In recent years,perovskite materials have attracted significant research interest in photovoltaics due to their advantages of easy synthesis,low cost,high absorption coefficient,and long carrier diffusion distance.In addition to their high performance in photovoltaic fields,perovskites have attracted extensive research interest in other optoelectronic devices,such as light-emitting diodes(LEDs),photodetectors and lasers.Among the perovskite materials,all-inorganic metal halide perovskite quantum dots(Cs Pb X₃,X=Cl,Br,I)have excellent optical properties,such as high photoluminescence quantum efficiency,tunable emission in the whole visible range,obvious quantum confinement effect and large exciton binding energy.Therefore,they have attracted extensive research interests in the field of next generation displays and solid state lighting.However,Cs Pb X₃ quantum dots synthesized by existing methods,in which oleic acid(OA)and oleylamine(OLA)are usually used as surface chelating ligands.The highly dynamic binding between the ligands and the quantum dot surface leads to the losing of ligands during the purification process,leaving a large number of defects on the surface of quantum dots.The non-radiative recombination and low stability caused by these defects are considered to be the main problems that need to be solved urgently in the practical application of perovskite quantum dots in high efficiency light emitting diodes.How to effectively passivate the defect sites on the surface of perovskite quantum dots and improve the performance and stability of perovskite quantum dot LED devices has become a research hotspot.Therefore,this thesis proposes a multi-ligand passivation strategy to effectively passivate the surface defects of Cs Pb Br₃ quantum dots,prepares LED devices with excellent performance and high stability,and by replacing the organic charge transport materials in the devices with inorganic materials to further improve device stability.The specific research content of this thesis is as follows:Firstly,we use a multi-ligand passivation strategy to prepare a highly fluorescent and highly stable Cs Pb Br₃ quantum dot colloidal solution,that is,zwitterionic ligands(C3-sulfobetaines)and hexylamine ligands are used to replace part of the oleylamine ligands to modify the Cs Pb Br₃ quantum dots.The results have shown that the multi-ligand passivation strategy can effectively passivate the surface defects of Cs Pb Br₃quantum dots.Among them,the binding kinetics of zwitterionic ligands to the surface of quantum dots is more stable through chelation,and the affinity of hexylamine ligands to the electropositive sites on the surface of quantum dots is stronger than that of oleylamine ligands.This strategy effectively suppresses non-radiative recombination,improves the radiation efficiency,and improves the colloidal stability of Cs Pb Br₃quantum dots.Secondly,using multi-ligand passivation Cs Pb Br₃ quantum dots as the active layer,a Cs Pb Br₃ quantum dot LED device was prepared.The results show that the multi-ligand passivation Cs Pb Br₃ quantum dot LED device exhibits excellent performance:the maximum brightness is 2062 cd/m²,the maximum current efficiency is 5.94 cd/A,and the EQE peak value is as high as 7.28%.Not only the photoelectric performance,in terms of stability,the multi-ligand processed Cs Pb Br₃ quantum dot LED device shows superiority.Afterwards,the device structure was optimized and the organic transport materials were replaced with inorganic transport materials(Ni O and Zn O).The results show that the Cs Pb Br₃ quantum dot LED device with inorganic transport layer performs well in terms of the light emitting efficiency,and stability of the LED device.