Effects of Br Substitution on Inorganic Rudorffite AgBiI4 for Stable, Pb-Free Solar Cells

Despite the rapid development of Pb-based perovskites, the presence of toxic Pb and insufficient stability remain discouraging factors for the commercialization of perovskite solar cells. Therefore, research on Pb-free absorbers exhibiting long-term stability is required. Herein, AgBi(I1-xBrx)(4) thin films having a hexagonal rudorffite structure were fabricated using a solution process in ambient atmosphere for cost-effective and environmentally benign photovoltaics. Br substitution increases the grain size and results in a pinhole-free morphology. Furthermore, photoluminescence analyses confirm that Br substitution reduces the trap-state density. Consequently, device efficiency is enhanced through Br substitution. Importantly, Br substitution results in considerably improved device stability, with devices maintaining 80 % of their initial efficiency for 26 days in ambient atmosphere without encapsulation.