Density Functional Theory Study of the Electronic and Optical Properties of SnSe₂/MoSe₂ Heterostructures under Strain and Electric Field: Implications for Optoelectronic Devices

The vertical stacking of various two-dimensional (2D) layered materials to create van der Waals heterostructures (vdWHs) has received great attention as a promising material for developing nanoelectronic and optoelectronic devices. This is because such structures can inherit the unique and favorable properties of a single 2D material. In this study, a SnSe 2 /MoSe 2 vdWH model was built for the first time using the first-principles approach, and its electronic and optical properties were systematically investigated. The results reveal that the SnSe 2 /MoSe 2 vdWH exhibits a type-II heterostructure with a 0.167 eV indirect band gap, which facilitates the separation of photogenerated electron–hole pairs. Notably, the electrical characteristics of the SnSe 2 /MoSe 2 vdWH can be easily controlled by applying an external electric field or biaxial strain. Specifically, a positive electric field or tensile strain narrows the band gap, whereas a negative electric field or compressive strain widens the band gap. The energy band alignment shifts from a type-II to a type-I configuration when a negative electric field of E = −0.6 V Å –1 or a compressive strain of 10% is applied. Furthermore, SnSe 2 /MoSe 2 vdWHs exhibit improved optical absorption across the visible to ultraviolet regions compared to the individual monolayers of SnSe 2 and MoSe 2 . Additionally, the absorption can be influenced by external tension and electric fields. Specifically, under significant compressive strains (10%), the ultraviolet absorption peak reaches 33.5%. Interestingly, a red shift occurs with tensile strain or a negative electric field, whereas a blue shift occurs with compressive strain or a positive electric field. The proposed SnSe 2 /MoSe 2 vdWH in this study offers valuable insights into electronic and optoelectronic device development, particularly in the context of photovoltaic devices, where enhanced ultraviolet absorption can lead to improved light-to-electricity conversion efficiency.