Sb₂Se₃ as a bottom cell material for efficient perovskite/Sb₂Se₃ tandem solar cells

Antimony selenide (Sb₂Se₃) semiconducting material possesses a band gap of 1.05–1.2 eV and has been widely applied in single-junction solar cells. Based on its band gap, Sb₂Se₃ can also be used as the bottom cell absorber material in tandem solar cells. More importantly, Sb₂Se₃ solar cells exhibit excellent stability with nontoxic compositional elements. The band gap of organic–inorganic hybrid perovskite is tunable over a wide range. In this work, we demonstrate for the first time a perovskite/antimony selenide four-terminal tandem solar cell with a specially designed and fabricated transparent electrode for an optimized spectral response. By adjusting the thickness of the transparent electrode layer of the top cell, the wide-band-gap perovskite top solar cell achieves an efficiency of 17.88%, while the optimized antimony selenide bottom cell delivers a power conversion efficiency of 7.85% by introducing a double electron transport layer. Finally, the four-terminal tandem solar cell achieves an impressive efficiency exceeding 20%. This work provides a new tandem device structure and demonstrates that antimony selenide is a promising absorber material for bottom cell applications in tandem solar cells.