The Rise of Chalcohalide Solar Cells: Comprehensive Insights From Materials to Devices

While lead-halide perovskites achieve high efficiencies, their toxicity and instability drive the search for safer materials. Chalcohalides, combining chalcogen and halogen anions in versatile structures, emerge as earth-abundant, nontoxic alternatives for efficient photovoltaic (PV) devices. A wide variety of chalcohalide materials, including pnictogen metals-, post-transition metals-, mixed-metals- and organic-inorganic metals-based chalcohalides, offer diverse structural, compositional, and optoelectronic characteristics. Some of these materials have already been experimentally synthesized and integrated into PV devices, achieving efficiencies of 4-6%, while others remain theoretically predicated. Despite these advancements, significant challenges must be addressed to fully realize the potential of chalcohalides as next-generation PV absorbers. This review provides a comprehensive insight of the fundamental properties of chalcohalide materials, emphasizing their unique structures, highly interesting optoelectronic and dielectric properties, to fuel further research and guide the development of high-efficiency chalcohalide solar cells. Various synthesis techniques are discussed, highlighting important and potentially overlooked strategies for fabricating complex quaternary and pentanary chalcohalide materials. Additionally, the working principles of different device structures and recent advances in fabricating efficient chalcohalide solar cells are covered. We hope that this review inspires further exciting research, innovative approaches, and breakthroughs in the field of chalcohalide materials.