Phase rearrangement for minimal exciton loss in a quasi-2D perovskite toward efficient deep-blue LEDs via halide post-treatment

Electroluminescence efficiencies of deep-blue quasi-two-dimensional (quasi-2D) perovskites are limited by a lack of post-treatment strategies that can both construct an ideal energy-transfer tunnel structure minimizing the exciton losses and passivate chlorine vacancies. Herein, multi-functional halide post-exchange is demonstrated for fabricating efficient deep-blue quasi-2D perovskite light-emitting diodes (PeLEDs). This post-treatment suppresses detrimental chlorine vacancies in the perovskite lattice, resulting in an efficient deep-blue perovskite emitter. Synergistically, the spontaneous phase rearrangement occurs via merging between neighboring low-n phases to higher-n phases. The narrowed 2D phase distribution enhances excitonic-energy transfer to the target bulk phase with fewer energy transfer steps, each of which is accompanied by adverse energy loss by exciton dissociation. Efficient deep-blue PeLEDs with a maximum external quantum efficiency of 4.97% are realized, emitting at 470 nm. Device lifetimes are also elongated as a synergetic benefit. This work provides an effective approach as a step closer to designing high-performance deep-blue PeLEDs for practical applications.