Improved Performance of Ultrathin Cu(InGa)Se2 Solar Cells With a Backwall Superstrate Configuration

A backwall superstrate device structure that outperforms conventional substrate Cu(In,Ga)Se-2 devices for thin absorbers is described. The backwall structure of glass/ITO/MoO3/Cu(In,Ga)Se-2/CdS/i-ZnO/Ag utilizes a MoO3 transparent back contact to allow illumination of the device from the back. The device performance has been improved by modifying the Cu(In,Ga)Se-2, including alloying with Ag to form (AgCu)(InGa)Se-2 absorber layers. In addition, sulfized back contacts including ITO-S and MoS2 are compared. Interface properties are discussed based on the XPS analysis and thermodynamics of reactions.