Regulation of Additive-Cs⁺ Interactions for Efficient Cesium Copper Iodide Light-Emitting Diodes

Molecular additives are widely used to improve the film quality and optoelectronic performance of solution-processed metal halides, owing to their diverse interactions with metal-halide precursors. However, the relationship between additive-precursor interaction strength and the optoelectronic performance of metal halides remains unclear. In this study, we investigate cesium copper iodide (Cs–Cu–I) light-emitting diodes (LEDs) incorporating crown ether (CE) additives and demonstrate that the additive-Cs⁺ interactions can significantly influence the device performance. By regulating the additive-Cs⁺ interaction strength, we achieve Cs–Cu–I LEDs with a peak external quantum efficiency of 4.5%, over 20 times higher than that of the control device. The remarkable EQE enhancement is primarily attributed to the suitable additive-Cs⁺ interactions, which enable a gradual release of free precursors to participate in the crystallization of Cs–Cu–I, thus improving the crystalline quality of emissive films. This work not only provides valuable insights into the rational design of molecular additives for copper halide LEDs but also offers guidance for other metal halide optoelectronic devices, particularly those involving additive-precursor interactions.