Abstract

We report the electroluminescent properties of a well-known Cu(I) complex based on P∧P-type ligands—specifically bis[2-(diphenylphosphino)phenyl] ether (DPEphos)—and N∧N-type ligands, namely, 2,9-dimethyl-1,10-phenanthroline (dmphen), [Cu(dmphen)(DPEphos)]BF4 (Cu1), as the emissive layer, transitioning from a light-emitting electrochemical cell (LEEC) to an organic light-emitting diode (OLED) configuration. No electroluminescence was observed in simple LEEC-type devices. However, the progressive introduction of injection and transport layers, and using 1,3-bis(carbazol-9-yl)benzene (mCP) as a host matrix, enabled efficient emission centered at 530 nm. We achieved effective charge balance and confinement of the recombination zone within the host through systematic optimization of host and transport layer thicknesses. We further investigated the effect of Cu1 doping concentration in mCP (0%-30%) on the device performance and emission color. While 10% doping yielded the highest luminance and efficiency, the emission color was also modulated—from green with bluish hues at low doping to yellowish green at higher levels—demonstrating a straightforward strategy for color tuning using a single Cu(I) complex. Although Cu1 is not the most efficient emitter available, its well-characterized nature and response to device architecture make it an ideal model for understanding structure-function relationships. This study offers valuable insights into layer engineering and compositional tuning, which can facilitate the development of more efficient and color-tunable devices with next-generation Cu(I)-based emitters. © 2025 Author(s).