A Cu‐Pb Hybrid Layer Architecture as New Structural Prototype for High‐Efficiency 2D Double Perovskite Broadband Emitters

Two‐dimensional (2D) organic lead halide perovskites have emerged as promising next‐generation luminescent materials due to their high chemical versatility and excellent broadband light emission properties. However, their practical applications are often limited by low photoluminescence quantum yields (PLQYs) caused by insufficient exciton confinement and extended charge‐carrier diffusion lengths within the 2D anionic layers. To overcome these limitations, we developed a novel multicomponent structural engineering strategy that led to the design of [AMP]2Cu2PbX8 double perovskites (AMP = 4‐(Aminomethyl)piperidinium, X = Br‐ and I‐). These materials feature [Cu2PbX8]4‐ monolayers consisting of alternating corner‐sharing [Cu2X6]4‐ dimers and [PbX6]4‐ octahedra. Compared to the negligible luminescence observed in 2D [AMP]PbX4 analogs, the [AMP]2Cu2PbX8 compounds demonstrate strong broadband yellow‐orange emission originating from self‐trapped excitons (STEs), achieving high PLQYs exceeding 48%. Comprehensive spectroscopic analysis and theoretical studies reveal that the incorporation of [Cu2X6]4‐ dimers simultaneously enhances exciton binding energy, electron/hole effective mass, exciton confinement efficiency and STE self‐trapping depth, which are all critical factors contributing to the improved PLQY. This work successfully demonstrates a new class of 2D double perovskites with exceptional luminescent performance, advancing perovskite chemistry through a dual‐engineering strategy that concurrently optimizes both material structure and photophysical properties.