Theoretical insights into a potential lead-free hybrid perovskite: Substituting Pb²⁺ with Ge²⁺

In recent years, perovskite solar cells have been considerably developed, however the lead in the absorber MAPbI₃ is a potential threat to the environment. To explore potential alternatives, the structural and electronic properties of MAGeX₃ (X = Cl, Br, I) were investigated using different density functional theory methods, including GGA-PBE, PBE-SOC, HSE06 and HSE-SOC. The results implied that MAGeI₃ exhibits an analogous band gap, substantial stability, remarkable optical properties, and significant hole and electron conductive behavior compared with the so far widely used absorber MAPbI₃. Moreover, the calculations revealed that the energy splitting resulting from the spin-orbit coupling is evident on Pb, moderate on Ge, I and Br, and negligible on Cl. Our work not only sheds some light on screening novel absorbers for perovskite solar cells but also deepens the understanding of these functional materials.