Unraveling the Degradation Mechanism of Halogen Ion Migration in Sky-Blue Perovskite Light-Emitting Diodes

A common strategy to obtain blue- or sky-blue-emitting perovskite light-emitting diodes (PeLEDs) is to incorporate chlorine into the bromine-based perovskites. However, reliability is a crucial and challenging issue. The underlying degradation mechanism of these mixed-halide PeLEDs under continuous electrical bias remains incompletely understood. Herein, we elucidate the degradation mechanism of sky-blue mixed-halide PeLEDs by comparing one device without electrical bias and another with continuous electrical bias. Through the comprehensive microscopic and spectroscopic studies, we identify several key factors that account for the device degradation: (i) electric-field induced Joule heating; (ii) pinhole formation under electrical bias; and (iii) halogen ion migration toward the interface of electron-transport layer and cathode. We also substantiate that chloride ion migration plays a more dominant role than bromide in the device degradation of the sky-blue mixed-halide PeLEDs. The experimental results are fully supported by our theoretical calculations. Our results provide guidance for an in-depth understanding of the degradation mechanism of the mixed-halide PeLEDs and pave the way to obtaining stable PeLEDs based on compositional engineering strategies in the future.