Vacuum Dual-Source Thermal-Deposited Lead-Free Cs₃Cu₂I₅ Films with High Photoluminescence Quantum Yield for Deep-Blue Light-Emitting Diodes

Deep-blue emitters are greatly desirable for preparing white light-emitting diodes and enhancing the color gamut of full-color display. The deep-blue lead halide perovskite light-emitting diodes (PeLEDs) exhibit far inferior performance compared to green and red counterparts and suffer from lead toxicity, hampering their applications. Nontoxic, stable, and wide band gap zero-dimensional (0D) Cs3Cu2I5 with relatively high exciton binding energy has great potential as deep-blue emitters. However, the development of PeLEDs remains a huge challenge due to the difficulties in preparing a high-quality Cs3Cu2I5 film and device design, arising from an inherent wide band gap together with deep ionization potential. Here, a continuous and pin-hole-free Cs3Cu2I5 thin film with deep-blue emission centered at 440 nm was prepared by the dual-source thermal evaporation approach, and a high photoluminescence quantum yield of 58% was achieved, corresponding to significant enhancement of 61% compared with that of the Cs3Cu2I5 thin film synthesized by solution processes. Furthermore, saturated deep-blue PeLEDs at the Commission Internationale de L’Eclairage (CIE) coordinates (0.15, 0.08) were obtained by employing an electron-transfer layer composed of a 1,4,5,8,9,11-hexa-azatriphenylene hexacarboni-trile (HAT-CN) and N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) organic heterojunction to realize the effective hole blocking, rendering an external quantum efficiency of approximately 0.1%. These results will be extensively beneficial to wide band gap material and device preparation.