Quasiparticle GW Calculations on Lead-Free Hybrid Germanium Iodide Perovskite CH3NH3GeI3 for Photovoltaic Applications

Lead-free organic-inorganic halide perovskites have gained much attention as nontoxic alternatives to CH 3 NH 3 PbI 3 in next-generation solar cells. In this study, we have examined the geometric and electronic properties of methylammonium germanium iodide CH 3 NH 3 GeI 3 using density functional theory. Identifying a suitable functional to accurately model the germanium halide perovskites is crucial to allow the theoretical investigation for tuning the optoelectronic properties. The performance of various functionals (PBE, PBE+D3, PBEsol, PBEsol+D3, HSE06, and HSE06+D3) has been evaluated for modelling the structure and properties. The calculation of electronic properties was further refined by using the quasiparticle GW method on the optimized geometries, and that has an excellent agreement with the experiment. We report from our GW calculations that the characteristic of the density of states for CH 3 NH 3 GeI 3 resembles the density of states for CH 3 NH 3 PbI 3 and the effective masses of the charge carriers of CH 3 NH 3 GeI 3 are comparable to the effective masses of CH 3 NH 3 PbI 3 as well as silicon used in commercially available solar cells.