Synergistic energy harvesting and catalysis in B₂SSe-MSSe (M = Mo, W) van der Waals heterostructures

In this study, we employed density functional theory (DFT) to investigate the structural, electronic, optical and photocatalytic properties of B₂SSe-MSSe (M = Mo, W) van der Waals heterostructures (vdWHs). Due to the presence of different chalcogen atoms on either side of these Janus monolayers, multiple possible stacking patterns of B₂SSe-MSSe heterostructures were constructed and analyzed. Their mechanical, thermal, and dynamical stabilities are confirmed via binding energies, Born criteria, ab initio molecular dynamics (AIMD) simulations, and phonon spectrum calculations. The weighted electronic band-structure analysis via both PBE and HSE06 functionals confirmed a type-II band alignment with an indirect bandgap. The intrinsic asymmetry of Janus materials introduces out-of-plane polarization and vertical electric fields, which facilitate efficient charge-carrier separation and migration, suppress recombination, and enhance photo-oxidation and visible-light absorption. Electrostatic potential profiles, charge density differences, and Bader charge analysis confirm interlayer charge transfer from the MSSe to the B₂SSe monolayer, indicating p-type doping in the MSSe and n-type doping in the B₂SSe of B₂SSe-MSSe vdWHs. Higher carrier mobility in specific cases, verified via effective mass calculations, further promotes efficient charge transfer to the surface and reduces recombination across the interface of B₂SSe-WSSe vdWHs, making them promising for light-detection and -harvesting applications. The imaginary part of dielectric function (ε ₂(ω)) indicating strong visible light absorption capacity. The valence and conduction band edge potentials were calculated to assess their photocatalytic suitability. The results demonstrate that B₂SSe-MSSe vdWHs exhibit suitable band edges for overall water splitting at pH = 0, with the valence and conduction band edges straddling the redox potential window, enabling spontaneous oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) under visible light irradiation. These findings underscore the potential of the B₂SSe-MSSe (M = Mo, W) vdWHs for optoelectronic and photocatalytic hydrogen production applications and offer a valuable framework for designing the next-generation optoelectronic and photoharvesting devices.