Unveiling 2D Rb ₃ Bi ₂ I ₆ Cl ₃ and Rb ₃ Bi ₂ I ₃ Cl ₆ perovskites for optoelectronic, solar cell and photocatalytic applications

The removal of harmful lead from perovskite materials has led to a surge in interest in lead-free perovskite-based solar cells. Using density-functional theory (DFT) and a numerical simulation method using the solar cell capacitance simulator SCAPS-1D. This work aims to advance the field of lead-free perovskite solar cells by conducting a comparative analysis of lead-free perovskite materials. WIEN2k is employed to explore the structural, electronic and optical properties of the two dimensional (2D) halide perovskites Rb₃Bi₂I₆Cl₃ and Rb₃Bi₂I₃Cl₆, while their solar cell (SC) efficiency is estimated using SCAPS-1D. The reported structural properties are aligned with the experimental values. The electronic properties of Rb₃Bi₂I₆Cl₃ and Rb₃Bi₂I₃Cl₆ reveal their direct band gap semiconducting nature with band gaps of 2.02 and 1.99 eV, respectively. Their optical properties reveal that the compounds are activated under visible light, making them ideal for optoelectronic device and SC applications. To model the efficiency of these compound-based solar cells, MoO₃ is optimized as an electron transport layer (ETL); TiO₂-SnS₂ is optimized as a hole transport layer (HTL), and the respective thickness of the ETL, HTL and absorber are optimized as 180, 150 and 900 nm, respectively. Rb₃Bi₂I₆Cl₃ and Rb₃Bi₂I₃Cl₆ are used as the absorber layer (AL). Optimized solar cell devices based on FTO/TiO₂-SnO₂/Rb₃Bi₂I₆Cl₃ and Rb₃Bi₂I₃Cl₆/MoO₃/Ni achieved short-circuit current densities of 9.02 and 10.11 mA cm^-2, open-circuit voltages of 1.41 and 1.35 V, fill factors of 84.69% and 83.93%, and power conversion efficiencies (PCE) of 11.39% and 11.52%, respectively. Additionally, photocatalytic analysis demonstrates that all of the materials can evolve H₂ from H⁺ and O₂ from H₂O/O₂. Additionally, the compound under study can reduce CO₂ to produce HCOOH, CO, HCHO, CH₄OH and CH₄. Based on these findings, 2D perovskites could be used in optoelectronic devices, photovoltaics, and photocatalysis-especially for water splitting and CO₂ reduction driven by visible light. These results facilitate future studies aimed at developing fully inorganic lead-free perovskite-based photovoltaics and photocatalysts.