MoSe₂ layer formation at Cu(In,Ga)Se₂/Mo Interfaces in High Efficiency Cu(In_{1- x}Ga_x)Se₂ Solar Cells

Abstract

MoSe 2 layers formed at the interface between Cu-In-Ga-Se and Mo layers were studied by X-ray diffraction and high resolution transmission electron microscopy. Various composition Cu-In-Ga-Se films such as Se, Cu-Se, In-Ga-Se and Cu-rich Cu-In-Ga-Se were deposited on Mo coated glass substrates by physical vapor deposition. For the case of the Se/Mo interface, a MoSe 2 layer of about 100 Å thickness was observed. The c -axis of the MoSe 2 grains were found to be oriented normal to the surface of Mo layer. For the Cu-Se/Mo and Cu-rich Cu-In-Ga-Se/Mo structures, the thickness of the MoSe 2 layers found at the interface was thin. For the case of the In-Ga-Se/Mo structure, a 0.1 µm thick interfacial MoSe 2 layer was observed whose c -axis was oriented parallel to the Mo surface. The microstructure of the In-Ga-Se/Mo film was similar to that of the device quality CIGS/Mo structure deposited by the “3-stage” process. A formation mechanism for the MoSe 2 layers occurring during the “3-stage” process is proposed.