Oriented tuning the photovoltaic properties of γ-RbGeX3 by strain-induced electron effective mass mutation

Based on the concept of green environmental protection, we hope to find a substitute for lead perovskites to reduce the pollution and achieve high photoelectric conversion efficiency. In this paper, the structural, electronic and optical properties of gamma-RbGeX3 (X = Cl, Br and I) hybrid perovskites are investigated by density functional theory (DFT) calculations. The result shows that the gamma-RbGeI3 has direct band gap of 1.38 eV and exhibits strong optical absorption in the visible light spectrum. However, the electron effective mass in the z direction is larger, which restricts the carrier mobility in the ( 0 0 1) direction. The blemish can be overcome by applying the -2% strain in the z direction, which causes the mutation of electron effective mass from 1.35 to 0.09 with little influence on the value of the band gap and the hole effective mass. These above findings also offer a new view to explore the inorganic perovskite for solar cell absorbers.