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

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.