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

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. A host‐guest design strategy is adopted to simultaneously improve the exciton radiative recombination and charge injection efficiency in lead‐free [dppb]2Cu2I2 emitters. Consequently, efficient green‐emitting LEDs with a record external quantum efficiency of 13.39% and a large‐area emitting area up to 81 cm2 with uniform emission are realized, substantially surpassing those of recently reported Cu halide‐based devices.