<p>Hydrogen and other clean chemical fuels that can be produced using solar-driven catalysis on semiconductors offer a promising alternative to burning fossil fuels and meeting the increasing worldwide demand for energy. Because of their distinct structural features and applications, they have attracted considerable attention recently in the fields of photocatalysis and optoelectronics. In the current study, the structural, electronic, optical, and photocatalytic properties of the Cs₃Bi₂I₉, Cs₂CuBi₂I₉, and Cs₂AgBi₂I₉ perovskites are extensively evaluated using density functional theory. These compounds are found stable both mechanically and thermodynamically, and their structural parameters are comparable with experimental results. These compounds are semiconducting in nature with bandgap values of 2.0&#xa0;eV, 1.90&#xa0;eV, and 1.71&#xa0;eV, respectively, and are visible-light-active, making them promising materials for optoelectronic and photocatalytic uses. All of these compounds can oxidize H₂ O/O₂ to O₂ and H⁺ to H₂, according to the photocatalytic study. The compounds can also reduce CO₂ to CO, CH₄, HCHO, and CH₄OH, and similarly, can reduce N₂ to NH₃, N₂H₄, and N₂H₅. The photocatalytic efficiency of these compounds for water splitting is above the targeted value for industrial application and also achieves adequate efficiency for CO₂ and N₂ reduction compared to the other materials. In the future, these findings could lead to the development of lead-free, totally inorganic perovskite photovoltaics and photocatalysts that the improve photovoltaic and photocatalytic performance and have potential use in optoelectronics, photovoltaics, and photocatalysis, in particular for visible-light-driven processes such as water splitting, CO₂ reduction, and N₂ fixation.</p> Graphical Abstract <p></p>