Electronic and photochemical properties of hybrid binary silicon and germanium derived Janus monolayers

The electronic structures and optical properties of a novel class of hybrid binary Janus materials derived from IV-V groups were investigated using first principles calculations. The computational results demonstrated that, except for Ge₂NAs, all the other five structures of M₂XY monolayers (M = Si, Ge; X, Y = N, P, As; X ≠ Y) have excellent thermal and dynamical stabilities. Janus Si₂NP, Si₂NAs, Si₂PAs and Ge₂NP are semiconductors with direct band gaps spanning the range between 0.82 and 2.49 eV. Notably, the hybrid M₂XY materials exhibit highly efficient absorption within the visible light region, which are greatly higher than their pristine MX structures. Janus Si₂PAs and Ge₂PAs possess appropriate band edge alignments that straddle the water redox potentials in the pH range from 0 to 14, making them promising photocatalysts for water splitting under visible light. Our calculations further demonstrate that the catalytic selectivity for the water splitting reaction could be achieved through the hybrid Janus M₂XY, where, for instance, Ge₂NP appears to facilitate only the oxidation, but not the reduction of water under certain conditions. This outcome provides a new route for the design of novel photocatalysts with improved efficiency and selectivity.