Extraordinary Strong Band‐Edge Absorption in Distorted Chalcogenide Perovskites

All existing solar cell materials including hybrid perovskites show rather small absorption coefficient ( α ) of ≈10 4 cm −1 in the bandgap ( E g ) transition region. The weak band‐edge light absorption is an essential problem, limiting conversion efficiency particularly in a tandem solar cell. Herein, all distorted chalcogenide perovskites (BaZrS 3 , SrZrS 3 , BaHfS 3 , and SrHfS 3 ) are found experimentally to exhibit extraordinary high α exceeding 10 5 cm −1 near E g , indicating the highest band‐edge α among all known solar cell materials. The giant absorption in the E g region, which is consistent with the first principles, arises from the intense p–d interband transition enabled by dense S 3p valence states. For solar cell application, low‐gap BaZrS 3 derivatives, Ba(Zr,Ti)S 3 and BaZr(S,Se) 3 , are further synthesized. Among the possible candidates of top‐cell materials, an earth‐abundant and nontoxic Ba(Zr,Ti)S 3 alloy shows great potential, reaching a maximum potential efficiency exceeding 38% in a chalcogenide perovskite/crystalline Si tandem architecture.