Stabilizing the Electroluminescence of Halide Perovskites with Potassium Passivation

Halide perovskites have been of great interest for light-emitting diodes (PeLEDs) in recent years because of their excellent photo- and electroluminescence properties. However, traps/defects and ion migration in devices under high external driving voltage or current are yet to be overcome. In this work, it is found that upon potassium (K) addition to a CsPbBr3/Cs4PbBr6 (3D:0D = 0.85:0.15) perovskite, a locally disordered 0D Cs4-xKxPbBr6 phase is formed with nearly 0.35:0.65 admixture of 0D:3D, along with an unreacted KBr phase potentially passivating the surface and grain boundaries. The formation of CsPbBr3 nanocrystals (similar to 10 nm) confined within the Cs4-xKxPbBr6 matrix accompanied by larger CsPbBr3 grains (similar to 50 nm) is further confirmed by highresolution transmission electron microscopy. In addition, the kinetics of ion migration was characterized with Auger electron spectroscopy and double-layer polarization using capacitive-frequency measurements, revealing significantly lower hysteresis, halide ion migration, and accumulation for the K-incorporated samples during device operation, resulting in substantial improvements in LED performance and stability.