Extraordinary Strong Band‐Edge Absorption in Distorted Chalcogenide Perovskites
Yukinori Nishigaki, Takayuki Nagai, Mitsutoshi Nishiwaki, Takuma Aizawa, Masayuki Kozawa, Kota Hanzawa, Yoshitsune Kato, Hitoshi Sai, Hidenori Hiramatsu, Hideo Hosono, Hiroyuki Fujiwara
Abstract
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.