Unraveling Size-Dependent Ion-Migration for Stable Mixed-Halide Perovskite Light-Emitting Diodes.

Mixed-halide perovskites show tunable emission wavelength across the visible light range, with optimum control of the light color. However, color stability remains limited due to the notorious halide segregation under illumination or an electric field. Here, we present a versatile path toward high-quality mixed-halide perovskites with high emission properties and resistance to halide segregation. Through systematic in- and ex-situ characterizations, key features for this advancement are proposed: a slowed and controllable crystallization process can promote achieving halide homogeneity, which in turn ensures thermodynamic stability; while downsizing perovskite nanoparticle to nanometer-scale dimensions can enhance their resistance to external stimuli, strengthening the phase stability. Leveraging this strategy, we develop devices based on CsPbCl 1.5 Br 1.5 perovskite that achieve a champion external quantum efficiency (EQE) of 9.8% at 464 nm, making it one of the most efficient deep-blue mixed-halide perovskite light-emitting diode (PeLED) to date. Particularly, the device demonstrates excellent spectral stability, maintaining a constant emission profile and position for over 60 minutes of continuous operation. We further showcase the versatility of this approach with CsPbBr 1.5 I 1.5 PeLEDs, achieving an impressive EQE of 12.7% at 576 nm. This article is protected by copyright. All rights reserved.