Extraordinary Strong Band-Edge Absorption in Distorted Chalcogenide Perovskites

摘要

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)S3 and BaZr(S,Se)_3, are further synthesized. Among the possible candidates of top-cell materials, an earthabundant 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.