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.