Effects of Br Substitution on Inorganic Rudorffite AgBiI 4 for Stable, Pb‐Free Solar Cells

Abstract 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(I 1−x Br x ) 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.