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 Cs_4–xK_xPbBr₆ 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 (∼10 nm) confined within the Cs_4–xK_xPbBr₆ matrix accompanied by larger CsPbBr₃ grains (∼50 nm) is further confirmed by high-resolution 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.