Janus MoAZ 3 H (A = Ge, Si; Z = N, P, As) monolayers: a new class of semiconductors exhibiting excellent photovoltaic and catalytic performances.

Due to the asymmetrical structure in the vertical direction, Janus two-dimensional (2D) monolayer (ML) materials possess some unique physical properties, holding great promise for nanoscale devices. In this paper, based on the newly discovered MoA 2 Z 4 (A = Si, Ge; Z = N, P, As) ML, we propose a class of 2D Janus MoAZ 3 H ML materials with good stability and excellent mechanical properties using first-principles calculations. We demonstrate that the novel Janus MoAZ 3 H ML materials are all semiconductors with bandgaps ranging from 0.69 to 2.44 eV, giving rise to good absorption in the visible light region. Especially, both MoSiN 3 H and MoGeN 3 H MLs can be used as catalysts for producing hydrogen through water splitting. This catalytic property is much more efficient than that of the MoA 2 Z 4 ML, attributed to the intrinsic electric field induced by the vertical asymmetry effectively separating electrons and holes. More importantly, the carrier mobility of the MoAZ 3 H ML is up to 10 3 -10 4 cm 2 V -1 s -1 due to the large elastic modulus or small effective mass. Additionally, the electronic properties of the MoAZ 3 H ML can be easily tuned by strain. Our results suggest a new strategy for designing novel 2D Janus materials, which not only expands the members in the 2D MA 2 Z 4 -based Janus family, but also provide candidates with excellent performances in photovoltaic and catalytic fields.