Near-unity blue luminance from lead-free copper halides for light-emitting diodes

Copper(I)-based halides are emerging as attractive nontoxic candidates to rival the lead-halide perovskites for optoelectronic applications. Herein, the zero-dimensional organic-inorganic copper halide [N(C₂H₅)₄]₂Cu₂Br₄ was proposed as a novel luminescence material. Its single crystals (SCs) were synthesized with a facile approach, realizing photoluminescence quantum yield (PLQY) up to 97.08% and superior stability. Importantly, TEA₂Cu₂Br₄ SC exhibited a broadband blue emission around 463 nm with a large Stokes shift of 183 nm and a long photoluminescence (PL) lifetime up to 50 μs. In particular, the solution-processed polycrystalline films maintain a high PLQY of 94.73%. Based on temperature-dependent and time-resolved PL measurements and first-principles calculations, we propose a multi-channel phosphorescence mechanism for the broadband blue emission of this novel material. In addition, tunable PL of the polycrystalline films from sky-blue to deep-blue was realized. The solution processed electroluminescence devices employing the multiple blue emitters were readily achieved in the coordinate range of CIE from (0.15, 0.17) to (0.15, 0.04). Notably, the sky-blue EL device achieves a brightness of 85 cd/m² and an external quantum efficiency of 0.11%. Our work thus inspires the design and synthesis of novel copper-based emitters and paves a way for future applications in white light-emitting diodes and full-color display.