Optimizing Device's Optical Structure For Highly Luminescent Perovskite Light-Emitting Diodes With Mixed-Cations

Perovskite light-emitting diodes(PeLEDs)have good commercial prospects in the field of displaying and lighting due to their tunable bandgap and high color purity.At present,solution spin coating method is generally used to fabricate MAPbBr3 film,but there exists the defects of poor film morphology and porosity,thus results in the overlarge leakage current.In this thesis,the control of the growth process of the perovskite films was firstly realized to obtain a good perovskite film morphology.To promote the photoelectrical performance of the device,a micro-nano structure was introduced into the PeLED to reduce its optical Ioss.Meanwhile,the COMSOL software was employed to analyze the optical field distribution inside of PeLED with the micro-nano structure.To improve the stability of the device,the packaging techniques of PeLED was employed.The research mainly focused on:Primarily,the mixed-cation perovskite film was investigated by varying the doping ratio of Cs+,It demonstrated that the amount of Cs+played a significant role in the properties of PeLED.As the mixed-cation ratio is 3:7 and become Cs0..3MA0.7PbBr3 perovskite,it presented a uniform and dense perovskite film with the average grain diameter of 461 nm,which enhanced the radiation recombination efficiency of PeLED.Thus,the maximum brightness of PeLED increased from 13477 cd/m2 to 18557 cd/m2,and the maximum EQE rised from 0.26%to 0.36%.It optimized without changing the original color purity of the PeLED.Secondly,the nano-gratings structure was introduced into PeLED to improve its light extraction efficiency.By using COMSOL software,the influence of nano-gratings structure on optical field distribution inside of the device was analyzed.Besides,the patterned PDMS was employed to imprint submicro-gratings onto the Cs0..3MA0.7PbBr3-PEO film during annealing process.It exhibited the brightness of PeLED increased from 10406 cd/m2 to 30863 cd/m2,enhanced by a factor of 2.96.Also,its greatest EQE rose up from 0.27%to 0.58%,enhanced by a factor of 2.1 The enhancement was attributed two factors:On one side,the nano-imprinting resulted in the grain refinement of the provskite film during annealing,which improved the radiation recombination of the film.On the other side,the plasma effects arising from the patterned structure promoted the optical coupling output efficiency of the device.Finally,the influence of packaging process on perovskite films and devices was investigated.Three packaging methods,namely non-packaging,UV-curable adhesive packaging and epoxy resin packaging were utilized.The effects of water,oxygen and packaging materials on perovskite films were investigated by comparing the properties of PeLEDs.The results showed that UV-curable adhesive packaging device had the advantage in brightness and the epoxy resin packaging device presented the best EQE,the lowest current density and the excellent the breakdown characteristics.It indicated that the epoxy resin had strong permeability,which effectively passivated the surface defects of perovskite film and refined the perovskite grain,there by improving the performance of the devices.