Study On Quantum Dot Light-emitting Diodes With Ligand Exchange And Charge Transfer Layer Optimization

Quantum dots are increasingly applied in solar cells,biomarkers,photoelectric detection,lighting and display and other fields,due to their continuous size adjustable wavelengths,narrow bandwidth and high stability.Among these applications,quantum dot light emitting diodes gets the most attentions from researchers because of the characteristics such as,active luminescence,high stability,wide color gamut,etc.Since solution processing can be used to produce quantum dot light emitting diodes and reduce the cost of mass production,quantum dot light emitting diodes are expected to replace the organic light emitting diode display and become the next generation display technology.In this paper,quantum dot light-emitting diodes were fabricated by solution process of spin coating.And the performance influence of surface ligands exchange conditions and charge transport materials on quantum dot light-emitting diodes were studied.The main contents are as follows:(1)The effect of pH value on the ligand exchange of 3-mercaptopropionic acid on the surface of the quantum dots.Oleyl-amine and oleic acid ligands of quantum dots were mostly replaced by short chain 3-mercaptopropionic acid,and the effect of fluorescence property of quantum dots under different pH values conditions were investigated.The results show the fluorescence intensity increases with increasing pH value when pH<10.But when pH>10,the fluorescence intensity rapidly decreases with increasing pH value.After that,quantum dot light-emitting diodes were fabricated by in situ ligand exchange on the film by using 3-mercaptopropionic acid solution with a pH value of 10.The current and luminance tests show that the exchange ligands could promote the transport of carriers in the device,but the stability is not as good as that of the long chain ligands.(2)The influence of doped hole transport materials on the quantum dot light emitting diodes.Different ratios of high charge mobility material TAPC were added to the hole transport layer of PVK in the quantum dot light emitting diodes.When TAPC occupies a relatively high ratio,the uniformity of the hole transport layer is poor.When PVK:TAPC=3:1,it can keep the film uniformly and stabilize the luminescence at the same time,and as a result,improve the brightness and efficiency of the device.The maximum brightness is16200cd/m~2 and the maximum current efficiency was 5.02cd/A.(3)The effect of the solvent of the electron transfer material on the quantum dot light emitting diodes.4?5nm zinc oxide nanoparticles were synthesized as the electron transport materials of quantum dot light emitting diodes.As the limitation of the synthesis method,zinc oxide could not be directly dissolved in alcohol solvent.The effect of different solvents on the morphology of the film were investigated.The results show that ethanol with ethanol amine solvent system can obtain a much more uniform film and enhance the performance of the device,compared to the mixed solvent of chloroform and ethanol.The maximum brightness of the device is 22940cd/m~2 after the optimization and the highest current efficiency reaches 28.9cd/A.