Efficient and Stable Deep-Blue Emission from Lead-Free (TEA)₂Cu₂Br₄ for White LEDs

Abstract

Lead-free copper halides have emerged as promising candidates for solid-state lighting, yet many reported systems still face challenges of limited efficiency, severe self-absorption, or insufficient device stability. Here, we report the synthesis of transparent millimeter-sized single crystals of (C₈H₂₀N)₂Cu₂Br₄ (TEA₂Cu₂Br₄) via a facile antisolvent-assisted evaporation method. Structural analysis confirmed that bulky TEA⁺ cations encapsulate [Cu₂Br₄]²⁻ units, forming a spatially confined low-dimensional framework that promotes efficient radiative recombination of self-trapped excitons (STEs). TEA₂Cu₂Br₄ exhibits deep-blue emission at 478 nm with a large Stokes shift of 166 nm, a long photoluminescence lifetime of 54 μs, and an ultrahigh PLQY of 98%. The material demonstrates remarkable robustness against continuous illumination, thermal cycling, electrical bias, and ambient exposure, with decomposition occurring only above 300 °C. Furthermore, ultraviolet-excited WLEDs fabricated by integrating TEA₂Cu₂Br₄ with CsCu₂I₃ deliver balanced white emission with CIE coordinates of (0.3175, 0.3593), a correlated color temperature of 6138 K, and retain 93.8% of their initial electroluminescence intensity after 20 days of continuous operation. These results highlight TEA₂Cu₂Br₄ as a structurally well-defined, high-performance hybrid copper halide with strong potential for environmentally friendly solid-state lighting.