Theoretical study on photoelectric properties of lead-free mixed inorganic perovskite RbGe1-xSnxI3

The recent discoveries of lead-free halide perovskites have come into notice as promising photovoltaic materials due to their high solar-to-electrical efficiency conversion. However, these perovskites suffer from large effective masses, wide band gap and affected photovoltaic performance. It is well known that it is an effective means to overcome the above shortcomings by changing the metallic ion concentration and position for the inorganic perovskite. Herein, we study the geometrical, electronic, and optical properties of RbGe_1-xSn_xI₃ with various compositions of metal atoms by performing the Density Functional Theory (DFT). Besides, we systematically investigate how the doping positions of stannum (Sn) atoms affect the electronic structure by taking mixed metal RbGe_0.50Sn_0.50I₃ compound as an example. The results show that RbGe_1-xSn_xI₃ exhibits the semiconducting property with the tunable direct band gaps by changing its proportions. Compared to other two doping positions in the perovskite RbGe_0.50Sn_0.50I₃, the configuration with Sn atom at equator plane has better mobility of electron and optical absorption properties. Our works demonstrate that the modification of metal concentration and position will modulate the optoelectronic performance and photovoltaic properties of mixed metal perovskites.