Study On High Efficient Quasi-two-dimensional Perovskite Light-emitting Diodes

Quasi-two-dimensional?quasi-2D?perovskites with?A₁?₂?A₂?_n-1Pb_nX_3n+1 quantum well structures are considered as the potential electroluminescence?EL?materials due to their controllable quantum confine effect which would lead a high EL efficiency.However,the quasi-2D perovskite films fabricated with solution processing technologies consist of different n phases and orientated layers,which limits the performance of quasi-2D perovskite light-emitting diodes?Pe LEDs?.To improve the performance of Pe LEDs,it is essential to obtain perovskite thin films with large exciton binding energy,complete surface coverage and suitable morphology.Here some approaches are developed to improve the performance of quasi-2D Pe LEDs.?1?Poly?ethylene oxide?passivated quasi-2D perovskiteThe enhanced optical and electrical properties of quasi-2D perovskite achieved by poly?ethylene oxide??PEO?passivation.The introduction of PEO can not only passivate the surface defects of?PEA?₂MA_n-1Pb_nBr_3n+1 films,but also suppress the formation of low luminescent efficiency n=1 single-layered quasi-2D perovskite phase.The photoluminescence quantum yield?PLQY?of the composite film has been approximately increased by 350%compared with pure quasi-2D perovskite film.The EL devices based on PEO:quasi-2D perovskite composite film achieved a brightness of up to 41800 cd/m² and a maximal current efficiency of 25.1 cd/A.The EL intensity of the device with PEO passivation dropped to 70%of the initial value after around 7hours under a constant current density of 10 m A/cm²,which indicates the excellent operation stability.?2?The improved quantum well structureThe multi-phase mixtures contained in quasi-2D perovskite materials would cause nonradiative recombination at perovskite film surface.Here,a facile solution surface treatment is adopted to improve the multiple quantum well structure of quasi-2D perovskite emitting layer,which can reduce the influence of defect induced nonradiative recombination and the electric field induced dissociation of excitons in the Pe LEDs.The quasi-2D perovskite film with surface treatment exhibits a maximum PLQY of62.3%.Meanwhile,the EL device achieves a current efficiency of 45.9 cd/A.?3?Suppression of electric-field induced dissociation of excitonComparing the difference in quenching factors calculated from electric-field modulated PL and electric-filed depended lifetime of excited state of quasi-2D perovskite films,we found that the major electric-field induced dissociation of excitons happens in funnel energy transfer process that is one of key factors to result in efficiency roll-off at high drive voltage of quasi-2D Pe LEDs.The detrimental effect can be improved by doping cesium?Cs?cation in quasi-2D perovskite,which can improve the surface morphology and suppress the electric field induced dissociation of exciton in the Pe LEDs.The prepared quasi-2D perovskite?PEA?₂FA₂Pb₃Br₁₀ film with Cs doping exhibits a remarkable PLQY up to 74%.The Pe LEDs based on?PEA?₂FA_1.8Cs_0.2Pb₃Br₁₀shows a reduced efficiency roll-off green emission with maximum current efficiency of 55 cd/A.