Lead-Free Halide Perovskites KSiI3 and RbSiI3: First-Principles Insights into Structural Stability, Optoelectronic Properties, and Photocatalytic Water-Splitting Potential

Abstract

Lead-based halide perovskites, despite their remarkable optoelectronic properties, suffer from significant drawbacks, including toxicity and environmental instability, which hinder large-scale deployment in clean energy technologies. To address these concerns, lead-free halide perovskites have emerged as sustainable alternatives, offering comparable performance with reduced ecological and health risks. In this work, we present a comprehensive investigation into the structural, electronic, elastic, optical, and photocatalytic properties of the lead-free halide perovskites KSiI₃ and RbSiI₃. The formability and mechanical stability of both compounds were confirmed via tolerance factor and elastic constants, while the AIMD simulations confirms the thermal stability of both materials at 300 K. HSE functional was used to accurately capture their electronic and optical characteristics. It is found that KSiI₃ and RbSiI₃ are direct band-gap semiconductors (1.44 eV, 1.47 eV), highlighting their potential for photovoltaic applications. Furthermore, the photocatalytic behavior was examined, highlighting the influence of pH on the valence and conduction band edges, confirming that both materials meet the energetic requirements for water-splitting reactions, thereby demonstrating their suitability for photocatalytic hydrogen production.