Thin Film Deposition and Optical Properties of Cs-Cu-I System Via Mist Deposition with Various Precursor Compositions

Abstract

Cu-based metal halides, such as Cs₃Cu₂I₅ and CsCu₂I₃, are promising materials for light-emitting diodes, photodetectors, and scintillators because of their excellent optical properties, non toxicity, and high air stability. In this study, we deposited thin films of the Cs-Cu-I system using Mist deposition varying the precursor composition of CsI and CuI and investigated their optical properties. X-ray diffraction 2θ-ω revealed that the Cs-Cu-I system thin films deposited by Mist deposition showed peaks corresponding to Cs₃Cu₂I₅ and CsCu₂I₃ phases, with both phases existing in the composition of the concentration of Cu higher than Cs. Energy Dispersive X-ray Spectroscopy measurements presented the decreasing of Cs concentration in thin films compared to the precursor solution. The Cs-Cu-I system thin films exhibited blue and yellow emissions under UV radiation, originating from Cs₃Cu₂I₅ and CsCu₂I₃, respectively. Especially, by adjusting the composition properly, Cs₃Cu₂I₅ thin films achieved a photoluminescence quantum yield of 92.4% in thin films. This study paves the way for the thin film deposition and the application of Cu-based metal halide.