Fabrication And Optoelectric Performance Optimization Of Perovskite LEDs Based On 3D MAPbBr₃

Owing to high color purity,low defect density and easily manufacturing,organic/inorganic hybrid perovskite materials are considered as promising luminescent materials in the next generation of lighting and display.However,the poor quality and instability of perovskite films,low charge injection efficiency lead to the poor performance of perovskite light emitting diodes(LEDs).In this thesis,3D MAPbBr₃ was employed as an emission layer in the perovskite LED.Polyethylene oxide(PEO),MABr overdoping and encapsulation process were employed to optimize the films quality,control the photoelectric properties of the perovskite films and improve the stability of the perovskite LED,respectively.Finally,a stable perovskite LED with a maximum external quantum efficiency(EQE)of 1.55%was demonstrated.In this thesis,it intensively focused on:One-step solution growth method of perovskite film was optimized on the basis of perovskite crystal formation kinetics.The influence of the anti-solvent dropping time on the morphology,crystalline quality and optical properties of the perovskite film was discussed.Besides,a uniform pinhole-free and low surface defect density perovskite film was fabricated by doping PEO into the perovskite precursor solution.Thus,the current efficiency(CE)of the perovskite LED is improved by suppressing the leakage current and enhancing the radiation recombination of the device.The MAPbBr₃-PEO-based perovskite LED obtained a maximum brightness of 4665.1 cd m^-2,almost three times of the pristine LED.Additionly,the optimized perovskite LED demonstrated a maximum CE of 5.55 cd A^-1The overdoping behavior of MABr was investigated by adjusting the molar ratio of the perovskite precursor PbBr₂ and MABr.As MABr increases,the interaction between free charge and longitudinal optical phonons was found to be enhanced and the exciton binding energy of the perovskite material was reduced,resulting in emission broadening and blue shift of the photoluminescence(PL)spectra.Furthermore,the luminance of the perovskite LED increased from 3292 cd m^-2 to more than 10,000 cd m^-2,while the lifetime of the device was shortened from 15 min to 2.5 min.As the molar ratio between PbBr₂ and MABr varies to be 1:1.315,the perovskite film exhibited the apparent self-passivation,which leaded to the strongest PL emission and the longest decay lifetime.As a result,the corresponding perovskite LED achieved a good trade-off between the luminance and the lifetime.And the device demonstratted a maximum EQE of 1.55%and a maximum CE of 6.59 cd A^-1.The ultraviolet adhesives and glass plate were employed in encapsulation process to improve the stability of the perovskite LED.Perovskite films were characterized by using the X-ray diffraction(XRD)and PL spectrometer,which showed that the encapsulation can effectively improve the stability of MAPbBr₃.In the air for three days,the electroluminescence(EL)for unpackaged device can not be observed.As a comparison,the encapsulated device still maintained 91%of the initial EL intensity.Interestingly,the encapsulation enhanced the voltage endurance of the device.It demonstrated that the average breakdown voltage of encapsulated devices was 0.9 V higher than that of unencapsulated devices.This indicated that the degradation arising from the reaction between the water and oxygen in the air and MAPbBr₃ was obviously slowed down after the perovskite LED was encapsulated,thereby improving the stability and voltage resistance of the device.