Contrasting Effects of Sb and Bi Doping on the Photocatalytic Properties of Cs₂AgInCl₆: Role of Bi in Rapid Degradation of Organic Dyes

Lead-free halide perovskites are attractive materials for photocatalytic applications. The direct and indirect bandgap nature of materials influenced their photocatalytic properties, such that the indirect bandgap enhanced photocatalysis due to the reduced charge recombination process. In this work, we synthesized Cs2AgIn(1–x)SbxCl6 and Cs2AgIn(1–x)BixCl6 solid solutions using acid precipitation and hydrothermal methods to examine the photocatalytic degradation of organic dyes under identical experimental conditions. The synthesized samples were characterized by XRD, SEM, and UV–vis spectroscopy. A detailed structural analysis was performed on all compounds using powder and single-crystal XRD methods. The photocatalytic degradation of organic dyes was performed on all samples using a photocatalytic reactor in an ethanol solvent medium. The direct bandgap, Cs2AgInCl6, exhibited good photocatalytic degradation results, whereas the substitution of Sb3+ at the In3+ site in Cs2AgIn(1–x)SbxCl6 drastically reduced the efficiency of dye degradation. In contrast, indirect bandgap Cs2AgBiCl6 and their solid solutions, Cs2AgIn(1–x)BixCl6, were found to outperform Cs2AgInCl6 in dye degradation properties. The role of Bi in photocatalytic degradation was further analyzed by using ab initio density functional theory (DFT) calculations. The availability of 6s lone pair electrons and effective charge separation by the indirect bandgap enhanced the photocatalytic reactions in Cs2AgBiCl6. The rapid degradation of organic dyes using Bi-based halide perovskites is promising for designing highly efficient, stable, and visible light photocatalysts for potential applications.