Efficient Dual-Band White-Light Emission with High Color Rendering from Zero-Dimensional Organic Copper Iodide

Broad-band white-light emissions from organic-inorganic lead halide hybrids have attracted considerable attention in energy-saving solid-state lighting (SSL) applications. However, the toxicity of lead in these hybrids hinders their commercial prospects, and the low photoluminescence quantum yields (PLQYs) cannot meet the requirements for efficient lighting. Here, we report a highly efficient dual-band white-light emission from organic copper iodide, (C₁₆H₃₆N)CuI₂, which exhibits a high PLQY of 54.3% and excellent air stability. The single-crystalline (C₁₆H₃₆N)CuI₂ possesses a unique zero-dimensional (0D) structure, in which the isolated [Cu₂I₄]^2- dimers are periodically embedded in the wide band gap organic framework of C₁₆H₃₆N⁺. This perfect 0D structure can cause significant quantum confinement and strong electron-phonon coupling, which contributes to efficient emissions from self-trapped excitons (STEs). Photophysical studies revealed the presence of two self-trapped emitting states in [Cu₂I₄]^2- dimers, whose populations are highly sensitive to the temperature that governs the molecular environment for [Cu₂I₄]^2- dimers and the thermal activation energy of STEs. An ultraviolet (UV) excited white light-emitting diode fabricated using this single-phase white-light emitter exhibits a high color rendering index (CRI) of 78. The new material provides a promising emitter, having a high PLQY and a high CRI simultaneously, for SSL and display applications.