Exciton Dissociation and Long-Lived Delayed Components in High-Efficiency Quasi-Two-Dimensional Green Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites, consisting of multi-quantum wells (MQWs) separated by organic intercalating cations, exhibit high luminescence efficiency while the photophysical processes involved remain partially obscure due to the uncertainty of the MQWs structure. Herein, a synergetic dual-additive strategy is adopted to prepare quasi-2D perovskite films, where 18-crown-6 and tris(4-fluorophenyl)phosphine oxide are utilized to suppress the formation of low-dimensional perovskites, diminish defect density, and enhance photoluminescence quantum yield to 93.7%. Notably, a long-lived delayed component, spanning hundreds of microseconds, is identified for the first time in perovskite emitters, which correlates with exciton dissociation and recombination, and the differences in temperature-dependent radiative lifetime of the delayed components match with the luminescence properties. Finally, benefiting from lower trap density and more efficient energy-funneling, green PeLEDs treated with dual additives have achieved a high external quantum efficiency of 28.9% and a commendable operating half-lifetime of 17.8 h at an initial brightness of 500 cd m⁻². The observation of the long-lived delayed components, coupled with insights into exciton dissociation, provides a profound and comprehensive understanding of the fundamental carrier behavior in perovskite emitters and establishes a direct correlation between the properties of perovskite emitters and their photophysical processes.