Suppressing nonradiative decay via molecular configuration control in Cu(i)–halide clusters enables the fabrication of highly efficient green and green-sensitized blue OLEDs

Abstract

Copper(I) complexes are cost-effective and eco-friendly emitters, yet their device applications are hindered by broad emission, by limited film-forming ability, and especially by severe excited-state distortions that typically lead to low emission efficiency in the film state. Herein, to address these challenges, we propose a structural design strategy for highly efficient and sublimable copper(I)-bromide clusters by simultaneously incorporating donor–acceptor bisphosphine ligands and introducing ortho-methyl substitution. This design effectively suppresses intrinsic nonradiative decay by modulating the excited-state geometry, thereby achieving an exceptionally high photoluminescence quantum yield of 99% in doped films. Vacuum-deposited organic light-emitting diodes (OLEDs) using the optimized cluster [dtpb-Ac]₂Cu₂Br₂ as the terminal emitter achieve efficient green emission with a maximum external quantum efficiency (EQE) of 25.1%. Notably, an innovative strategy exploits the intrinsically broad emission of the copper(I)-bromine cluster to sensitize the deep-blue MR-TADF emitter ν-DABNA, achieving high-efficiency green-sensitized blue OLEDs with a maximum EQE of 28.7% and Commission Internationale de l’Eclairage (CIE) coordinates of (0.15, 0.19). As either a green dopant or a sensitizer, the device performance ranks among the best reported for copper(I)-based OLEDs. The current study presents promising molecular design and sensitization strategies to address the key challenges in developing high-performance copper(I)-based OLEDs.