A Prediction of All‐Inorganic Lead‐Free Halide Perovskites for Photovoltaic Application: Rb3Mo2Br9 and Rb3Mo2Cl9

Abstract Lead‐based organic‐inorganic hybrid perovskites show promise as photovoltaic materials due to their high energy conversion efficiencies. However, concerns regarding lead toxicity and the poor environmental and operational stability of the organic cationic group have limited their widespread application. To address these challenges, the design of all‐inorganic lead‐free halide perovskites offers potential solutions for photovoltaic applications. Here, two layered perovskite derivatives, Rb 3 Mo 2 Cl 9 and Rb 3 Mo 2 Br 9 , are explored, and their electronic, structural, and photovoltaic properties are analyzed using advanced theoretical calculations. Rb 3 Mo 2 Br 9 exhibits a suitable direct bandgap of 1.60 eV, making it a promising candidate for use as a light absorber in low‐cost, high‐efficiency solar cells. On the other hand, Rb 3 Mo 2 Cl 9 demonstrates a wide direct bandgap exceeding 1.70 eV, positioning it as a viable option for use as a top cell in tandem photovoltaic systems alongside silicon. Both materials display ideal optical properties in the visible light region and hold promise as excellent inorganic lead‐free perovskite alternatives.