A Type-II BiTeCl/SnSe₂ Heterostructure with High Photoelectric Conversion Efficiency and Tunable Optoelectronic Properties for Photovoltaic Applications

In this study, a Janus BiTeCl/SnSe₂ van der Waals (vdW) heterostructure is constructed and systematically investigated for its potential in solar cell applications using first-principles calculations. The heterostructure introduces distinct contact interfaces (Cl-Se and Te-Se), both exhibiting a type-II band alignment. However, the conduction band minimum (CBM) and valence band maximum (VBM) contributions vary, depending on the interface. The Cl-Se interface demonstrates a significantly higher power conversion efficiency (PCE) of 20.11%, attributed to the suitable bandgap of the SnSe₂ donor material and a smaller conduction band offset. Both interfaces exhibit enhanced optical properties compared to those of isolated BiTeCl and SnSe₂ monolayers. Additionally, the electronic structure of the heterostructure is tunable via biaxial strain and electric fields, enabling further optimization of the PCE. Moreover, optical absorption can be adjusted by biaxial strain and electric fields. These findings position the Janus BiTeCl/SnSe₂ heterostructure, particularly the Cl-Se interface, as a promising candidate for next-generation photovoltaic devices, offering both high efficiency and an external tunability.