# Film Deposition and Optical Properties of Cu-Based Metal Halide Cs3Cu2(I1–xBrx)5 Alloy via Mist Deposition

## TL;DR

Researchers developed a scalable method to deposit copper-based metal halide thin films with controllable optical properties for use in LEDs and photodetectors.

## Contribution

A scalable mist deposition technique for creating Cu-based halide alloy thin films with precise compositional control and high optical performance.

## Key findings

- Cs3Cu2(I1–xBrx)5 alloy thin films were successfully deposited via mist deposition with precise halogen composition control.
- The films exhibited blue photoluminescence peaks and high photoluminescence quantum yields up to 92.4%.
- Long photoluminescence lifetimes were observed, indicating emission from self-trapped excitons.

## Abstract

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(I1–xBrx)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.