Extraordinary Strong Band-Edge Absorption in Distorted Chalcogenide Perovskites

All existing solar cell materials including hybrid perovskites show rather small absorption coefficient (alpha) of approximate to 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 (BaZrS3, SrZrS3, BaHfS3, and SrHfS3) are found experimentally to exhibit extraordinary high alpha exceeding 10(5) cm(-1) near E-g, indicating the highest band-edge alpha 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 BaZrS3 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.