Interplay of Janus Polarization and Interfacial Electric Fields Governing Carrier Dynamics in MoS2/MoSSe Heterostructures

It is crucial to understand the role of polarization and the built-in electric field in heterostructures of two-dimensional materials, as these factors significantly affect carrier dynamics, interfacial properties, and device performance. Here, we combine first-principles calculations with nonadiabatic molecular dynamics simulations to investigate the electronic structure and excited-state carrier dynamics of MoS2/MoSSe heterostructures. We show that the interplay between the intrinsic polarization of Janus MoSSe and the interface-induced electric field strongly modulates interlayer charge transfer. This dual-field coupling drives a transition between type-I and type-II band alignments and switches the dominant carrier relaxation pathways from intralayer recombination to interlayer charge separation. Carrier relaxation is further governed by the interplay between nonadiabatic coupling and phonon-assisted transitions. These results identify polarity reversal as an effective strategy for tuning charge-transfer pathways and excited-state dynamics in van der Waals heterostructures, and provide guidance for designing two-dimensional optoelectronic and photocatalytic materials.