Geometric structure and photovoltaic properties of mixed halide germanium perovskites from theoretical view

Abstract Inspired by the high efficiency of mixed halide perovskite CH3NH3PbI3-xClx due to the long diffusion and superior optical property, we pay our attention to the mixed halide germanium perovskite. In this paper, we present a detail theoretical investigation of geometric and electronic structure of mixed halide perovskite CH3NH3GeI3-xClx to predict its charge transport and optical properties. The calculated results show that this system exhibits tunable direct bandgap from 1.9 eV for CH3NH3GeI3 to 2.8 eV for CH3NH3GeCl3 compounds. With the increase of iodine atom doping ratio, the transport and optical properties significantly improve. In addition, we systematically discuss how the electronic structure depends on the doping position of iodine atoms by taking mixed halide CH3NH3GeI1Cl2 compound as examples. The results prove the mixed halide CH3NH3GeI1Cl2 demonstrates more superior transport and optical properties by doping iodine atoms at polar plane. This work will help to deepen the understanding of halogen doping mechanism by changing the doping proportion and doping position and these findings may lay foundation for experimental design to obtain higher photovoltaic properties in future.