Energy Transfer-Dominated\nQuasi-2D Blue Perovskite\nLight-Emitting Diodes

Abstract

The bromide–chloride mixed quasi-two-dimensional\n(2D) perovskite,\nwith a natural quantum well structure and tunable exciton binding\nenergy, has gained significant attention for high-performance blue\nperovskite light-emitting diodes (PeLEDs). However, the relative importance\nof having a low trap state density or efficient exciton transfer for\nhigh-efficiency electroluminescence (EL) performance remains elusive.\nHere, two molecules with the benzoic acid group, sodium 4-fluorobenzoate\n(SFB) and 3,5-dibromobenzoic acid (DBA), are used to modulate the\nphase distribution and trap state to explore the effect between energy\ntransfer and defect passivation. As a result, when the <i>n</i> = 1 phase is inhibited in both films, the DBA@SFB-modified perovskite\nfilms achieve a higher photoluminescence quantum yield (PLQY) than\nthe SFB-modified perovskite films due to effective defect passivation.\nHowever, DBA@SFB-modified PeLEDs exhibit lower external quantum efficiency\n(EQE) compared to SFB-modified PeLEDs due to the poor exciton transfer\nbetween the low-dimensional phase. This demonstrates that passivation\nstrategies may enhance photoluminescence through reducing nonradiative\nrecombination, but the effect of phase distribution is pivotal for\nEL performance by efficient energy transfer in quasi-2D perovskites.\nFemtosecond time-resolved transient absorption measurements confirm\nthe fastest carrier dynamics in SFB-modified perovskite films, further\ncorroborating the above result. This work provides useful information\nabout phase modulation and defect passivation for high-efficiency\nblue quasi-2D PeLEDs.