Van der Waals heterojunction interface passivation using ZnS nanolayer and enhanced photovoltaic behavior of semitransparent ultrathin 2D-MoS₂/3D-chalcogenide solar cells

Along with highly efficient Cu(In_1-x,Ga_x)Se₂ (CIGSe)-based thin-film solar cells, versatile solar cells are urgently required to meet a variety of functional needs, such as photovoltaic (PV) power conversion, transparency, ultrathinness, and light weight. To meet these needs, a semitransparent ultrathin (STUT) CIGSe solar cell with two-dimensional (2D) transition metal dichalcogenide (TMD) as the buffer layer is proposed as a prospective next-generation solar cell structure that exhibits advantages based on both the distinguishable optical properties of 2D TMDs and the high efficiency of CIGSe-based solar cells. However, the application of 2D TMDs on top of CIGSe is challenging because the surface of 2D TMDs is nominally and supposedly flat and smooth, while that of CIGSe absorbers is typically rough, and their combination is prone to defect formation at the interface. To overcome degradation due to interfacial defects, a 2D-MoS₂/ZnS/CIGSe semitransparent ultrathin solar cell was designed by inserting a ZnS nanolayer for heterojunction interface passivation, and the photovoltaic properties of the device were found to be improved. Furthermore, based on the binding energies of each layer, the energy band structures of n-MoS₂/p-CIGSe with and without a ZnS passivation layer are suggested, and the related implications for device performance are discussed.