Janus SMoZAZ′ (A = Si, Ge; Z, Z′ = N, P, As; Z ≠ Z′) monolayers: potential water-splitting photocatalyst with low carrier recombination rate

Abstract

To achieve efficient solar hydrogen conversion through photocatalytic technology, it is crucial to investigate a photocatalyst that demonstrates exceptional solar light absorption and high electron–hole separation efficiency. So far, Janus materials have been recognized as a promising photocatalyst due to their outstanding catalytic performance. In this work, we conducted a comprehensive investigation using first principles calculations to explore the stability, photocatalytic properties, optical properties, carrier mobility, and water molecules adsorption on the structural surface of 2D Janus SMoZAZ′ (A = Si, Ge; Z, Z′ = N, P, As; Z ≠ Z′) monolayer. Our findings reveal that SMoNGeAs and SMoPGeAs monolayers are thermally unstable, while the other 10 structures exhibit both dynamic and thermal stability. By employing the HSE06 functional calculation, we found that SMoNSiP, SMoNSiAs, and SMoNGeP monolayers demonstrate metallic properties. On the other hand, SMoPSiN, SMoAsSiN, SMoPSiAs, SMoAsSiP, SMoPGeN, SMoAsGeN, and SMoAsGeP monolayers exhibit indirect or direct band gap semiconductor properties. Notably, SMoPSiN, SMoAsSiN, SMoAsSiP, SMoPGeN, SMoAsGeN, and SMoAsGeP monolayers possess favorable band edge positions, leading to their excellent photocatalytic performance. Due to the different atoms at the top and bottom of the SMoZAZ′ monolayers, there is an internal electric field within the structure. Moreover, the notable difference in electron and hole mobility in the same direction enhances the efficient separation of electrons and holes. In the following investigation, we explore the effects of biaxial strain and external electric field on the electronic, photocatalytic, and optical properties of SMoZAZ′ monolayers. Finally, we examine the adsorption behavior of water molecules on the surface of SMoZAZ′ structures. These insights provide favorable evidence for Janus SMoZAZ′ monolayers to become an efficient photocatalyst with water decomposition performance.