Lead-free double perovskite Cs 2 Au 2 Br 6 for high-efficiency solar cells: a DFT and SCAPS-1D study

Abstract Lead toxicity remains a major obstacle to the commercialization of halide perovskites, despite their remarkable photovoltaic performance. To address this limitation, this study explores the lead-free double perovskite compound Cs 2 Au 2 Br 6 as an alternative absorbing material. A combined approach based on density functional theory (DFT) and numerical simulation via SCAPS-1D was used to evaluate its structural, electronic, optical, and photovoltaic properties. Ab initio calculations reveal that Cs 2 Au 2 Br 6 is a direct bandgap semiconductor with a bandgap of 1.023 eV, a high absorption coefficient of 10 5 cm −1 , and superior thermodynamic stability, making it compatible with efficient sunlight absorption. Based on these characteristics, we modeled a solar cell with an ITO/TiO 2 /Cs 2 Au 2 Br 6 /spiro-OMeTAD/Mo structure, analyzing the effects of the absorbing layer thickness, doping density, and band alignments. The optimized structure achieves a power conversion efficiency of 22.31%, demonstrating the strong potential of this material for thin-film photovoltaic applications. These results make a significant contribution to the search for alternative non-toxic photovoltaic materials and position Cs 2 Au 2 Br 6 as a promising candidate for the next generation of sustainable and high-performance solar cells.