Exploring electronic and optical properties of Ge-based perovskites under strain: Insights from the first-principles calculations

Organic-inorganic hybrid perovskites have attracted extensive attention as promising photovoltiac materials for high-efficiency solar cells. In this study, strain effects on the material properties of Ge-based perovskites are fully investigated by the first-principles calculations. The results indicate that the structural, mechanical, electronic and optical properties of CH3NH3GeX3 (X = Cl, Br, I) are sensitive to external modulations. The band gaps of three Ge-based halide perovskites are well predicted by using the HSE06 functional. By increasing the compressive strain, the band gaps of three compounds decrease. A suitable band gap (1.36 eV) of CH3NH3GeI3 can be obtained under a strain of −3%. Moreover, the calculated elastic constants further imply that this compound is stable under this condition. The relationship between the band gap variation and geometry change under the compressive strain is revealed. These results are useful for understanding the effects of strain on the material properties of semiconductors and guiding the experiments to improve photovoltaic performance of Ge-based perovskites.