Efficient Large‐Area (81 cm²) Ternary Copper Halides Light‐Emitting Diodes with External Quantum Efficiency Exceeding 13% via Host‐Guest Strategy

Abstract Ternary copper (Cu) halides are promising candidates for replacing toxic lead halides in the field of perovskite light‐emitting diodes (LEDs) toward practical applications. However, the electroluminescent performance of Cu halide‐based LEDs remains a great challenge due to the presence of serious nonradiative recombination and inefficient charge transport in Cu halide emitters. Here, the rational design of host‐guest [dppb]₂Cu₂I₂ (dppb denotes 1,2‐bis[diphenylphosphino]benzene) emitters and its utility in fabricating efficient Cu halide‐based green LEDs that show a high external quantum efficiency (EQE) of 13.39% are reported. The host‐guest [dppb]₂Cu₂I₂ emitters with mCP (1,3‐bis(N‐carbazolyl)benzene) host demonstrate a significant improvement of carrier radiative recombination efficiency, with the photoluminescence quantum yield increased by nearly ten times, which is rooted in the efficient energy transfer and type‐I energy level alignment between [dppb]₂Cu₂I₂ and mCP. Moreover, the charge‐transporting mCP host can raise the carrier mobility of [dppb]₂Cu₂I₂ films, thereby enhancing the charge transport and recombination. More importantly, this strategy enables a large‐area prototype LED with a record‐breaking area up to 81 cm², along with a decent EQE of 10.02% and uniform luminance. It is believed these results represent an encouraging stepping stone to bring Cu halide‐based LEDs from the laboratory toward commercial lighting and display panels.