Low‐Operating‐Voltage Yellow‐Green LEDs Based on Rationally Designed Copper‐Iodide Hybrid Clusters

ABSTRACT The energy efficiency of conventional phosphor‐converted light‐emitting diodes (LEDs) is limited by thermal losses of light down‐conversion. This has driven interest in developing cost‐effective, phosphor‐free LEDs as a promising alternative for solid‐state lighting. Recently, copper‐iodide hybrid clusters exhibit considerable potential for LED lighting, attributed to their efficient broadband emission, facile solution‐based processing, and environmental benignity. Nonetheless, the device performance is limited by high operating voltages, primarily due to a low valence‐band maximum, inefficient carrier injection, and inadequate carrier transport of present copper‐iodide hybrid cluster emitters. To address this bottleneck issue, we propose a rational design of copper‐iodide hybrid clusters by integrating alkoxy chains and carbazole‐derived functional groups. The alkoxy chain improves the solubility and film‐forming properties, and the carbazole unit modulates the energy level positions, collectively enabling the formation of an ultrathin, uniform emissive layer with enhanced carrier injection and transport. As a result, the fabricated yellow‐green LED exhibits a low turn‐on voltage of 2.8 V and a high luminance of 565.5 cd m −2 at 4 V, which are superior to previously reported copper‐iodide hybrid cluster‐based LEDs. This cluster‐regulation strategy via ligand engineering offers a promising pathway to develop high‐performance copper‐iodide hybrid cluster‐based LEDs for solid‐state lighting.