Out-of-plane dipole-modulated photogenerated carrier separation and recombination at Janus-MoSSe/MoS2 van der Waals heterostructure interfaces: an ab initio time-domain study

Abstract

Out-of-plane mirror symmetry-breaking provides a powerful tool for engineering the electronic properties and the exciton behavior of two-dimensional materials. Here, by combining time-domain density functional theory with nonadiabatic dynamics, we investigate the underlying mechanism of how the vertical dipole moment modulates the photoexcited carrier transport and the electron-hole recombination dynamics in polar Janus MoSSe/MoS₂ stacked heterostructures. It is shown that the stronger nonadiabatic coupling, interlayer-state delocalization and the built-in electric field caused by charge redistribution facilitate a more rapid photocarrier separation across the interface in the S/S stacked bilayer compared with the S/Se bilayer, explaining the experimentally observed stronger photoluminescence quenching effect in the S/S heterostructure. We also found that the photocarrier recombination of the heterostructure with the S/Se interface has a timescale up to nanoseconds, which is ∼4 times longer than that of the S/S bilayer. Such a prolonged recombination time originates from the dipole-weakened nonadiabatic coupling between occupied and unoccupied states instead of quantum coherence and the band gap effect. Overall, Janus MoSSe/MoS₂ heterostructures exhibit superior photocatalytic activity, reflecting the ultrafast photocarrier separation triggered by the built-in electric field, suppressed carrier recombination, high solar-to-hydrogen conversion efficiency and the strong absorption coefficient expanding from visible-light to near-infrared-light. The above atomistic and time-domain findings reveal the intrinsic dipole as an effective freedom to regulate the nonadiabatic photocarrier dynamics in Janus-based 2D heterostructures for efficient energy harvesting and optoelectronic applications.