Dion-Jacobson phase lead-free halide (PDA)MX4 (M=Sn/Ge; X=I/Br/Cl) perovskites: A first-principles theory

Hybrid lead (Pb) halide perovskites are widely regarded as promising materials for next generation of photovoltaic (PV) and optoelectronic (OE) devices owing to their high power conversion efficiency (PCE). To obtain green lead-free and excellent materials, the structural, electronic and optical properties of tin (Sn) and germanium (Ge) based single-layer Dion-Jacobson (DJ) phase perovskites (PDA)MX4 (M ​= ​Sn/Ge; X ​= ​I/Br/Cl) systems are investigated by carrying out first-principles theory. The calculation results indicate that all perovskites (PDA)MX4 have good thermal stability (at 300K), and the structural stability increases in the order of I–Br–Cl. These compounds are direct bandgap semiconductors, ranging from 1.26 to 1.81 ​eV ((PDA)SnX4) and 1.44–2.26 ​eV ((PDA)GeX4). Density of states (DOS) reveals that the band edge state mainly comes from the M-X bond and the organic molecule PDA is not directly involved in the contribution. Compared to Ge-based perovskites, the bandgap range of Sn-based perovskites is not only closer to the optimal bandgap requirement for perovskite solar cells (PSCs), but the optical properties reveal a slightly higher absorption coefficient for Sn-based perovskites in the visible light range. This suggests that (PDA)SnX4 perovskites are more favorable for PSCs applications. The theoretical study can provide strong support for the development of high-level perovskites materials in PV and OE devices.