Wide-Bandgap Subcells for Tandem Solar Cells: From Metal Halides to Metal Chalcogenides and Metal Chalcohalides

Efficient wide-bandgap (WBG) perovskite solar cells (PSCs) have propelled the rapid advancement of perovskite (PVK) tandem solar cells (TSCs). However, their commercialization remains impeded by the intrinsic instability of WBG PSCs, particularly under high-temperature maximum power point tracking conditions, underscoring the urgent need to develop robust, high-performance WBG top-cell materials. Here, we first summarize strategies to enhance the device performance of mainstream WBG metal halide PSCs, highlighting advances achieved through interface engineering, additive engineering, and related approaches. Then we evaluate the potential of metal chalcogenides solar cells as top-cell candidates, identifying their high processing temperatures as a key factor that constrains their integration in TSCs. Finally, we propose metal chalcohalides as promising top-cell materials for TSCs, owing to their suitable bandgaps, low toxicity, superior stability, and moderate processing temperatures. This review aims to provide design guidelines for the development of next-generation WBG top-cell materials in TSCs.