Structural Modulation Enables Bright and Efficient Cs–Cu–Cl Electroluminescence

ABSTRACT Cesium–copper–halide (Cs–Cu–X) perovskites are potential substitutes to lead‐halide perovskites for broadband electroluminescence (EL) in white light‐emitting diodes (LED) due to their non‐toxicity and unique self‐trapped exciton (STE) characters. Many efforts have been devoted to pushing up EL efficiencies of Cs–Cu–I LED devices, while there is no report of EL based on their Cl‐based counterparts yet. In this work, the EL of the Cs–Cu–Cl nanocrystals (NCs) was first demonstrated by a holistic structural modulation, whose champion device reached an external quantum efficiency of 2.02% and a high luminance of 3345 cd m −2 . The efficient bluish‐white EL was explored to collectively derive from the smooth film morphology, exciton inter‐band transition, triplet STE behavior, and promising electron transport ability of the Cs–Cu–Cl NC film. Additionally, the potential photophysical process for the broadband emission was proposed, collectively expanding the Cu‐based perovskite EL family for displays and lighting applications.