Cu2+-Induced Defect States in Lead-Free Cs2AgInCl6 Double Perovskite: Linking Photophysical Mechanisms to Photocatalytic and Plasma-Assisted CO2 Hydrogenation

Abstract Cs2AgInCl6 is an important lead-free double perovskite valued for its structural stability, potential in photocatalysis, and CO2 reduction, but its practical application is limited by intrinsically UV-dominated absorption. Through strategic defect engineering, this work demonstrates that Cu2+ doping effectively extends its absorption into the visible region. By combining theoretical calculations with experimental investigations, the study reveals how Cu2+ incorporation modifies the electronic structure and enhances the optical absorption. These results provide clear insights into the photophysical processes of the material, which are essential for improving its catalytic performance. A comprehensive DFT investigation reveals that the doping of Cu2+ prefers the substitution at the Ag+ site and results in the introduction of impurity states adjacent to the VBM. Experimental positron annihilation lifetime spectroscopy indicates the formation of defects with positron trapping characteristics upon Cu2+ doping. Variable temperature emission behavior is well explained by the Arrhenius equation with the activation energy of 93.3 meV and significant electron-phonon coupling strength indicated by the large value of the Huang-Rhys parameter (S = 19.46). Cu2+-doped Cs2AgInCl6 was investigated for photocatalytic applications. The Cu2+-doped sample exhibited 98% degradation of crystal violet dye. Furthermore, the material was explored for nonthermal plasma-assisted CO2 hydrogenation. An enhanced CO2 conversion efficiency was observed with Cu doping. We believe that our findings significantly enhance the understanding of the Cu2+-doped Cs2AgInCl6 system and provide valuable insights into its structure-property relationships for catalytic applications.