Enhanced performance of Janus XMSiY2 (X=S, Se; M=Mo, W; and Y=N, P) monolayers for photocatalytic water splitting via strain engineering

Abstract

In this article, using first-principles calculations, we propose XMSiY2 (X = S, Se; M = Mo, W; and Y=N, P) monolayers as a Janus form of MA2Z4 family and investigate their electronic, spintronic, and photocatalytic properties. The obtained band structures show that XMSiY2 monolayers are semiconductors with bandgaps ranging from 1.21 eV to 2.98 eV. Considering spin-orbit coupling, we observe that broken out-of-plane symmetry in the XMSiY2 structures leads to Rashba spin-splitting at the Γ point and lack of inversion symmetry results in Zeeman spin-splitting at the K point of the valence bands. The monolayers with W atom exhibit larger Zeeman spin-splitting (up to 0.479 eV for SeWSiP2) which indicates that XWSiY2 monolayers are promising materials for spintronic and valleytronic applications. Assisted by the large work function difference (Δ&varphi) between two surfaces of the Janus XMSiY2 monolayers, all the proposed structures satisfy the band alignment requirement for overall water splitting. Benefiting from strong solar absorption, large carrier mobility (up to 104 cm2 V−1 s−1) and huge difference between electron and hole mobilities, XMSiY2 monolayers are predicted to be high performance photocatalysts. Lastly, the effect of biaxial strain on the photocatalytic properties of the proposed monolayers is comprehensively investigated and it is found that compressive strain helps XMSiY2 structures to act as great photocatalysts for overall water splitting in an expanded range of pH. In addition, tensile strain can broaden and intensify the solar light absorption spectrum of XMSiY2 monolayers to achieve high performance photocatalysts.