Aqueous Instability of the Chalcogenide Perovskite BaZrS ₃

Chalcogenide perovskites, notably BaZrS₃, are emerging as promising alternatives to halide perovskites because of their attractive optoelectronic properties and predicted stability, with potential uses ranging from solid-state photovoltaics to aqueous photocatalysis. However, this promise is challenged by the well-known instability of many chalcogenides in water, where sulfur is readily oxidized. Here, we combine theoretical simulations and experimental approaches to study the aqueous stability of BaZrS₃. Our results show that BaZrS₃ undergoes rapid degradation not only in aqueous environment but even under water vapor (0.5 mbar), with light exposure further accelerating the process. This instability arises from sulfur oxidation, which is thermodynamically favored at the surface, with hydroxyl radicals (•OH) serving as key reactive species driving SO₄^2- formation. These findings provide critical insights into the aqueous stability and degradation mechanisms of chalcogenide perovskites, which are essential for the rational design of next-generation chalcogenide materials with enhanced stability and performance.