Enhanced photocatalytic activity of single-layered Hittorf's violet phosphorene by isoelectronic doping and mechanical strain: A first-principles research

t A systematic theoretically study is performed for violet phosphorus monolayer nanosheet with the objective of improving its photocatalytic activity in water splitting under visible light by isoelectronic elements (N, As, Sb, and Bi) doping and strain engineering. The results show that compared with N-, As-, and Sb-doping, the introduced Bi impurity can effectively enhance visible light absorption efficiency. By applying an in-layer strain for Bi-doping violet phosphorene, the modulation of band edges further narrows the band gap. In particular, for compressive strain, the absorption extends into the overall visible region, greatly increasing the visible light absorption efficiency, which could be attributed to the significant reduced band gap and highly dispersive electronic states around the topmost valence band. Moreover, the band alignments for Bi-doped violet phosphorus monolayer are well positioned for the feasibility of both photo-oxidation and photo-reduction of water within the range of 0 to -3% biaxial strains and 0 to -7% uniaxial strains. Hence, compressive strained Bidoped violet phosphorus monolayer can be a promising metal-free photocatalyst for water splitting owing to its improved visible light activity as well as the high carrier mobility.