Film Deposition and Optical Properties of Cu-Based Metal Halide Cs₃Cu₂(I_1- Br )₅ Alloy via Mist Deposition

Cu-based metal halides, such as Cs₃Cu₂I₅, have attracted significant attention as promising candidates for light-emitting diodes, photodetectors, and scintillators owing to their remarkable properties, including high photoluminescence quantum yield (PLQY), air stability, and nontoxicity. In particular, their emissive colors can be controlled by their halogen composition. However, a reliable technique for depositing halogen alloy thin films has not yet been established. Herein, we demonstrated the deposition of Cs₃Cu₂(I_1- Br )₅ alloy thin films via mist deposition, offering a scalable one-step method for Cu-based halide applications. X-ray diffraction and energy-dispersive X-ray spectroscopy revealed the successful formation of halogen alloy thin films with precise compositional control by varying the halide precursors. Additionally, alloy thin films formed via mist deposition exhibited high-coverage surfaces. Moreover, they exhibited blue photoluminescence peaks ranging from 440 to 456 nm under ultraviolet irradiation and a high PLQY of approximately 60%, reaching 92.4% for Cs₃Cu₂I₅ thin film. Furthermore, the photoluminescence decay curve exhibited microsecond-order long PL lifetimes indicative of emission from self-trapped excitons. This study represents a significant breakthrough in the development of scalable, high-performance Cu-based metal halide alloy thin films for optical applications.