Dipole-Driven Ultrafast Charge Separation in a Two-Dimensional Janus PtSSe/PtSTe van der Waals Heterostructure

Understanding ultrafast interlayer charge separation in the Janus heterostructures (HSs) is crucial for photocatalytic and photovoltaic applications. In this study, we systematically investigate the electronic structure, optical response, and ultrafast carrier dynamics in a Janus PtSSe/PtSTe van der Waals (vdW) HS using first-principles calculations and nonadiabatic molecular dynamics (NAMD). The Janus PtSSe/PtSTe HS is thermodynamically stable with a reduced indirect band gap of 0.36 eV arising from interlayer orbital hybridization and dipole-induced band realignment. The planar-averaged electrostatic potential analysis demonstrates an intrinsic built-in electric field that produces a staggered type-II band alignment within the redox potential of water, which promotes spatial separation of photoexcited charge carriers. The system exhibits strong low-energy optical absorption characterized by excitonic features, which are influenced by interlayer electronic coupling. The decoherence-induced surface-hopping (DISH) approach exhibits efficient phonon-assisted charge transfer between layers, characterized by significant nonadiabatic coupling (NAC) time (5.87–9.88 meV) and a brief electronic decoherence time (τd) of ∼96 fs. Janus PtSSe/PtSTe heterostructures possess ultrafast hole and electron transfer times of ∼0.13 and ∼0.97 ps, respectively, accompanied by a suppressed recombination time of ∼1.03 ps. The suitable type-II band alignment, along with ultrafast recombination dynamics, showcases the Janus PtSSe/PtSTe HS as a potential candidate for optoelectronic and photocatalytic devices.