Improved Performance of Ultrathin Cu(InGa)Se$_{\bf 2}$ 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/MoO
₃
/Cu(In,Ga)Se
₂
/CdS/i-ZnO/Ag utilizes a MoO
₃
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 MoS
₂
are compared. Interface properties are discussed based on the XPS analysis and thermodynamics of reactions.