Inspired by the high efficiency of mixed halide perovskite CH₃NH₃PbI_3-xCl_x 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 CH₃NH₃GeI_3-xCl_x 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.

由于长扩散和优异的光学性能，由于混合卤化物钙钛矿CH ₃ NH ₃ PbI _3-x Cl _x的高效率的启发，我们将注意力集中在混合卤化物锗钙钛矿上。在本文中，我们对混合卤化物钙钛矿CH ₃ NH ₃ GeI _3-x Cl _x的几何和电子结构进行了详细的理论研究，以预测其电荷传输和光学性质。所计算出的结果表明，该系统表现出可调谐直接带隙从1.9eV的为CH ₃ NH ₃ GEI ₃至2.8电子伏特为CH ₃ NH ₃GeCl ₃化合物。随着碘原子掺杂比的增加，传输性能和光学性能显着提高。另外，我们以混合卤化物CH ₃ NH ₃ GeI ₁ Cl ₂化合物为例，系统地讨论了电子结构如何取决于碘原子的掺杂位置。结果证明混合卤化物CH ₃ NH ₃ GeI ₁ Cl ₂通过在极平面上掺杂碘原子，证明了更优越的传输和光学性能。这项工作将有助于通过改变掺杂比例和掺杂位置来加深对卤素掺杂机理的理解，这些发现可能为将来获得更高光伏性能的实验设计奠定基础。