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 MAPbI(3) is a potential threat to the environment. To explore potential alternatives, the structural and electronic properties of MAGeX(3) (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 MAGeI(3) 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 MAPbI(3). 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.