Type-I/Type-II Transition of MoSe2/g-GaN van der Waals heterostructures mediated by biaxial strain and electric field for overall water splitting

Abstract

Nowadays, the fabrication of van der Waals heterostructures (vdWHs) from a variety of novel and existing two-dimensional materials has been regarded as an effective approach since it unravels excellent photocatalytic properties. Especially, transforming type-I to type-II vdWHs has gained significant attention due to efficient charge separation in photocatalytic, and photovoltaic devices. Here, we suggest two-dimensional MoSe2/GaN vdW heterostructures along with their mechanical, electronic, photocatalytic, and optical properties using hybrid density functional. The stability of vertically stacked MoSe2/GaN vdWHs is endorsed via binding energy, elastic constants, phonon dispersion, and ab-initio molecular dynamics simulation (AIMD). The HSE band structure and band alignment exhibit that MoSe2/GaN vdWH has a direct bandgap and suitable band edges for the hydrogen evolution reaction (HER) (ΔEc ≥ 0.36 eV) and oxygen evolution reaction (OER) (ΔEv ≥ 0.33 eV). The empirical and DFT schemes reveal that the MoSe2/GaN vdWHs have an intrinsic type-I band alignment with a direct bandgap and have adequately high kinetic over potentials to easily start the redox reaction. Furthermore, it’s also anticipated that type-I MoSe2/GaN vdWHs could be transformed to type-II vdWHs under mild strains and external electric fields, which would be favorable for effective charge separation and transportation. Notably, MoSe2/GaN vdWH shows a significantly high optical absorption of nearly 105 cm−1 in the visible and ultraviolet regions which could be more easily tuned with applied strain. Current work demonstrates that the design and modulation of MoSe2/GaN vdW heterostructures under strain and an electric field could open new directions for identifying promising photocatalysts in a wide solar spectrum.