Temperature-Dependent Structure–Property Relationship of Mn-Doped Cs2AgInCl6 Thin Films Impacts Its Application as a Self-Powered UV Photodetector

Lead-free halide double perovskites (DP) have garnered significant attention as potential substitutes for lead halide systems in optoelectronic applications. In this context, Cs2AgInCl6 (CAIC), a wide and direct bandgap DP, exhibits considerable promise as a material for ultraviolet photodetectors. However, the processing of thin films composed of CAIC nanocrystals (NCs) has demonstrated significant challenges. Herein, we study the temperature-dependent structure–property relationship of CAIC and Mn-doped CAIC NCs in this work. These films were pre- and post annealed at 100–300 °C to determine their effect on self-powered UV photodetectors. X-ray diffraction (XRD) and atomic force microscopy (AFM) data revealed that the perovskite phase of pristine and Mn-doped CAIC NCs remained stable until a specific annealing temperature was reached but significantly changed at 300 °C. Mn-doped samples show phase orientation changes at 150 °C due to lattice dilatation. Broad photoluminescence (PL) spectra are observed due to the emission of self-trapped exciton (STE) states from [AgCl]−5 octahedra deformation, which was strongly dependent on annealing temperatures. AFM, UV–visible absorption, Raman, and time-resolved PL investigations improved our understanding of surface physics, shape, optical properties, and charge carrier lifetimes. Finally, self-powered UV photodetectors were made using the best annealed 150 °C temperature of both pristine and Mn-doped CAIC NCs thin films exhibiting good figures of merits. These devices had responsivities of 0.03 and 0.06 A/W and on/off ratios of 129 and 271, respectively. The photophysical phenomena and device characterizations discussed in this study are anticipated to offer insights into the fundamental understanding and correlation of optoelectronic applications.