Tunable type-II band alignment in MoS₂/WSe₂ van der Waals heterobilayers under external stimuli for solar energy conversion

Vertical stacking of van der Waals (vdW) heterostructures combining multiple two-dimensional (2D) materials can surpass the performance limits of individual monolayers, opening new opportunities for optoelectronic devices. This study systematically investigates the geometric configuration and optoelectronic properties of the MoS₂/WSe₂ heterostructure using density functional theory (DFT) and chemical vapor deposition (CVD) experiments. The calculated bandgap is approximately 0.80 eV, and the system exhibits a type-II band alignment. Both biaxial strain and external electric fields can significantly modulate the bandgap and alignment. Under biaxial strain from −10% to +6%, the heterostructure maintains type-II alignment, while at +6%, it becomes metallic. The bandgap increases with strain and then decreases linearly between +6% and −6%. Under an external electric field from −0.4 to +0.3 V/Å, the bandgap decreases linearly. Beyond +0.3 V/Å, the alignment shifts to metallic; below −0.4 V/Å, it becomes type-I. The theoretical power conversion efficiency is ∼3.7% under normal conditions, but can be enhanced to 23.1% with proper tuning. The absorption spectrum is significantly broadened in the infrared region compared to individual layers, consistent with CVD experiments. Optical red and blue shifts are also observed under strain. These results highlight the potential of MoS₂/WSe₂ in photovoltaic and optoelectronic applications.