Different structural evolutions of inorganic perovskite CsGeI3

Abstract

Distinct from CsSnI₃ perovskite systems, the most stable non-centrosymmetric trigonal structure (space group of R3m) of the CsGeI₃ perovskite system was found in our calculations. We systematically studied the differences between two all-inorganic perovskites (CsSnI₃ and CsGeI₃) and proposed an unexpected distorted stable structure of the mixed Sn–Ge perovskite system (CsSn_0.5Ge_0.5I₃). All calculations of structural configuration and electronic properties were performed in the projector augmented-wave density-functional theory framework via the generalized gradient approximation (GGA). We found that the energy band evolutions of all-inorganic perovskites CsSn_xGe_1−xI₃ are completely different from those of the Sn–Pb perovskite compounds. After considering the spin–orbit coupling (SOC) effect, the bandgap evolution of the stable structure shows a linear change. The results unravel the previous controversial understanding of the atomic and electronic properties of Ge-based perovskite solar cells.