Thermally Stable Halide-Tuned CsPbX 3 /CdTe Four-Terminal Tandem Solar Cells with 25% Efficiency

The tandem integration of metal halide perovskites (MHP) and cadmium telluride (CdTe) thin-film technologies offers a clear pathway to exceed single-junction limits, but challenges remain in optimizing the bandgap alignment for efficient sunlight utilization and in ensuring long-term device stability. Here, we employ thermally stable all-inorganic cesium lead halide perovskites (CsPbX 3, X = Br, I) as wide-bandgap (WBG) top cells, where precise halide tuning enables bandgap optimization and efficient optical coupling with low-bandgap CdSeTe bottom cells in a four-terminal (4T) tandem configuration. The optimized devices achieve a record power conversion efficiency (PCE) of 25.13%, with 16.48% from the CsPbI 2 Br top cell and 8.65% from the CdTe bottom cell. Critically, the tandem architecture demonstrates operational stability under high-temperature stress up to 120 °C, highlighting the unique thermal robustness of all-inorganic CsPbX 3 absorbers. This study demonstrates that halide engineering in all-inorganic CsPbX 3 enables record efficiency and thermal stability in CdTe-based tandem photovoltaics.