Efficient band structure tuning of single-layer group IV-N semiconductors for visible-light-driven water splitting

Discovering more novel two-dimensional (2D) materials for solar water splitting has long been an essential topic in photocatalysis. The present study employs the hybrid functional (HSE06) theory to systematically investigate the electronic structures and band alignments with respect to the water redox potential of the mono-doping (cationic C and anionic P) and co-doping (B + O, B + S, Al + O, Al + S, and C + P) in monolayer IV-N (IVSi, Ge, and Sn) semiconductors. These donor-acceptor doping pairs are charge-compensated so that the doping systems can keep semiconductor character without recombination centers. Importantly, we discovered several co-doped IV-N structures to be highly promising solar water splitting photocatalysts, including (B + S) co-doped SiN, and (B + O), (B + S), and (C + P) co-doped GeN. They possess ideal band gaps (∼2.0 eV) for the maximum utilization of solar light, suitable band positions for the water redox reactions, and enhanced visible light response. Moreover, we propose that the band gap of the monolayer IV-N can be slightly reduced by the (Al + S) or (Al + O) co-doping, while heavily tailed by the (B + O) or (B + S) co-doping. Our research provides valuable insights for designing and synthesizing novel 2D IV-N photocatalysts for solar water splitting.