Efficient and Stable Deep-Blue 0D Copper-Based Halide TEA₂Cu₂I₄ with Near-Unity Photoluminescence Quantum Yield for Light-Emitting Diodes

Achieving deep-blue light with high color saturation remains a critical challenge in the development of white light-emitting diode (LED) technology, necessitating luminescent materials that excel in efficiency, low toxicity, and stability. Here, we report the synthesis of [N(C₂H₅)₄]₂Cu₂I₄ (TEA₂Cu₂I₄) single crystals (SCs), which exhibit deep-blue photoluminescence (PL) at 450 nm. These crystals are characterized by a significant Stokes shift of 180 nm, a long lifetime of 1.7 μs, and an impressive photoluminescence quantum yield (PLQY) of 96.7% for SCs and 87.2% for polycrystalline films. The zero-dimensional structure is attributed to the proper spacing of triangular inorganic units [Cu₂I₄]^2- by organic cations [N(C₂H₅)₄]⁺. This structural arrangement facilitates broadband deep-blue light emission with phosphorescent characteristics, as evidenced by temperature-dependent PL and time-resolved photoluminescence (TRPL) measurements. The band gap properties of TEA₂Cu₂I₄ were further elucidated through density functional theory (DFT) computations. Notably, the material exhibited minimal PL intensity degradation after continuous UV irradiation and one month of exposure to ambient conditions. Moreover, the polycrystalline film of TEA₂Cu₂I₄ maintained substantial deep-blue emission even after one year of storage. Utilizing TEA₂Cu₂I₄ thin film, we fabricated an electroluminescent device emitting deep-blue light with high color saturation, featuring CIE coordinates (0.143, 0.076) and a brightness of 90 cd/m². The exceptional photophysical properties of TEA₂Cu₂I₄ render it a highly promising candidate for optoelectronic applications.