First-principles investigation of potential water-splitting photocatalysts and photovoltaic materials based on Janus transition-metal dichalcogenide/WSe 2 heterostructures.

Two-dimensional materials have been shown to exhibit exotic properties that make them very interesting for both photo-catalytic and photo-voltaic applications. In this study, van der Waals corrected density functional theory calculations were carried out on heterostructures of MoSSe/WSe 2 , WSSe/WSe 2 , and WSeTe/WSe 2 . The heterostructures are semiconductors with type II band alignments which are advantageous for electron-hole pair separation. The HSE06 level electronic band gap was found to be 1.093 eV, 1.427 eV and 1.603 eV for MoSSe/WSe 2 , WSSe/WSe 2 , and WSeTe/WSe 2 respectively. We have considered eight high symmetry stacking patterns for each of the heterostructures, and among them the most stable stacking orders were ascertained based on the interlayer binding energies. The binding energies of the most stable MoSSe/WSe 2 , WSSe/WSe 2 , and WSeTe/WSe 2 heterostructures were found to be -0.0604 eV, -0.1721 eV, and -0.3296 eV with an equilibrium interlayer space of 5.75 Å, 4.05 Å, and 4.76 Å respectively. The Power Conversion Efficiency (PCE) was found to be 20, 19.98, and 18.24 percent for the MoSSe/WSe 2 , WSSe/WSe 2 , and WSeTe/WSe 2 heterostructures, respectively. The results show that they can serve as suitable photovoltaic materials with high efficiency, thus, opening the possibilities of developing solar cells based on 2D Janus/TMD heterostructures. The most stable heterostructures are also tested for photocatalytic water splitting applications and WSeTe/WSe 2 shows excellent photocatalytic activity by being active for full water splitting at pH = 7 and pH = 14, the MoSSe/WSe 2 heterostructure is good for the oxygen evolution reaction and WSSe/WSe 2 is active for the hydrogen evolution reaction.