Electric Control of Quasiparticle Band Gap and Electron–Hole Excitation in the Bilayer of Janus Structure MoSeS

The tunability of the band gap and optical properties of two-dimensional materials through electric fields has attracted significant attention for applications in electronics and optoelectronics. Recently, the transition metal dichalcogenide (TMD) MoSeS with Janus structure has been successfully synthesized with mirror symmetry broken and vertical dipole moment that distinguish it from conventional TMDs. When integrated into heterostructures, experimentally, it is revealed that Janus MoSeS can enhance interlayer coupling due to charge redistribution driven by the built-in electric field. In this paper, based on the many-body perturbation method, we investigate the quasiparticle electronic structure, electron–hole excitations, optical properties, and their evolution in the bilayer of Janus structure MoSeS with the external electric field. Due to the intrinsic dipole moment, the system has a type II band alignment, with the lowest-energy electron–hole excitations being of interlayer character. The quasiparticle band gap shows a persistent increase when the applied electric field is switched from the parallel to antiparallel direction of the intrinsic dipole moment. Consequently, the interlayer exciton exhibits a notable energy shift covering the infrared and red light spectrum, with the lifetime being tuned by up to four times on the microsecond scale. These findings suggest the potential application for Janus structure MoSeS in optoelectronics.