Precise band alignment modulation in MoS2/MoSSe heterojunctions via synergistic effects of spontaneous polarization and intrinsic electric fields

With the rapid advancement of optoelectronic devices, precisely regulating interfacial charge separation and light absorption in heterostructures has become a key challenge in overcoming performance bottlenecks. Here, MoS₂/MoSSe van der Waals heterostructures (vdWHs) are constructed via first-principles calculations to investigate how spontaneous polarization and built-in electric fields modulate structural stability, electronic properties, and optical characteristics. The results reveal that all configurations exhibit favorable thermodynamic stability. Notably, the intrinsic spontaneous polarization in Janus MoSSe plays a key role in determining the band alignment of MoS₂/MoSSe vdWHs. When the built-in and polarization fields converge at the interface (→←), a type-II band alignment forms; when they diverge (←→), a type-I alignment emerges. Further analysis demonstrates that the unique polarization field of MoSSe significantly enhances light absorption capability, achieving an absorption coefficient of 1.64 × 10⁶ cm⁻¹, representing a 36 % improvement over the monolayer MoSSe. This work provides theoretical insight into the polarization-field-induced modulation of heterostructure optoelectronic performance.