Crystal structure, bandgap, photoluminescence and resistivity properties of double perovskite Cs2AgBiCl6 single crystal and its thin film

Abstract

Lead-free Cs₂AgBiCl₆ double perovskite (Cs₂AgBiCl₆-DP) material, as a substitute for lead halide perovskite materials, has the advantages of environmental friendliness and high stability and has attracted much attention. However, the photoluminescence and conductive properties of Cs₂AgBiCl₆-DP have not been well studied. In this study, we prepared Cs₂AgBiCl₆-DP single crystals (SCs) by coordination–dissolution and coordination–precipitation method. Single- and powder-XRD, SEM, EDS, XPS, and EPR characterization were performed to confirm the structural characteristics of Cs₂AgBiCl₆-DP SCs. The Tauc diagram based on UV-visible (UV-vis) absorption spectroscopy reveals that the optical bandgap of Cs₂AgBiCl₆-DP SCs is extrapolated to 2.51 eV. Steady-state fluorescence spectra and time-resolved fluorescence spectra show that Cs₂AgBiCl₆-DP SCs has four fluorescence peaks entered at 443, 615, 650 and 723 nm and a fluorescence lifetime of about 4.16 ns. Cs₂AgBiCl₆/PMMA thin films were prepared by spin coating suspension (Cs₂AgBiCl₆ DP and PMMA in acetone solvent). The intensity of emission peak increases with the increase of light intensity at 369 nm. The intensity of emission peak located at 576 nm decreases with increasing incidence wavelength (from 369 to 454 nm) at 10 W m⁻². The emission intensity remains basically unchanged under continuous illumination for 9 hours at 369 nm at 5 W m⁻², which indicates that the Cs₂AgBiCl₆-DP thin film has good stability. In addition, the resistivity and block resistance show a negative exponential change with increasing temperature. These results provide some interesting ideas for the fields of photoluminescence and thermistors.