Efficient White Electroluminescence from Cu‐based Perovskite Achieved by High Hole Injection Core/Shell Structures

The copper-based (Cu-based) halide perovskite possesses eco-friendly features, bright self-trapped-exciton (broadband) emission, and a high color-rendering index (CRI) for achieving white emission. However, the limited hole injection (HI) of Cu-based perovskites has been bottle-necking the efficiency of white electroluminescence and thus their application in white perovskite light-emitting diodes (W-PeLEDs). In this study, we demonstrate a p-type cuprous sulfide (Cu₂S) lattice-connectedly capping over Cs₃Cu₂I₅ to form lattice-matched core/shell nanocrystals (NCs) by controlling the reactivity of sulfur (S) precursor in the synthesis. Interestingly, the resultant Cs₃Cu₂I₅/Cu₂S NCs significantly enhance the hole mobility compared to Cs₃Cu₂I₅ NCs. Besides, the photoluminescence quantum yield of Cs₃Cu₂I₅ NCs increases from 26.8% to 70.6% after the Cu₂S lattice-connected capping. Consequently, by establishing the structure of CsCu₂I₃/Cs₃Cu₂I₅/Cu₂S in W-PeLEDs, an external quantum efficiency of 3.45% and a CRI of 91 is realized, representing the highest reported electroluminescent performance in lead-free Cu-based W-PeLEDs. These findings contribute to establishing guidelines and effective strategies for designing broadband electroluminescent materials and device structures of PeLEDs.