Investigation of Sputtering Damage around pn Interfaces of Cu(In,Ga)Se2 Solar Cells by Impedance Spectroscopy

The application of impedance spectroscopy (IS) analytical theory to the characterization of the pn-interface of Cu(In,Ga)Se2 (CIGS)-based solar cells was investigated with a focus on directly observing the sputtering damage during deposition of an n-layer. We develop an equivalent circuit of the CIGS solar cell involving series and parallel resistances and a “capacitance-like element,” called a constant phase element (CPE), around the n-layer/p-CIGS interface. The CPE index of the impedance is shown to reflect　the quality of the n-layer/p-CIGS interface in terms of the sputtering damage and defects of the heterojunction. These results demonstrate the possibility of applying IS practically as a simple method for characterizing the sputtering damage around pn-interfaces in semiconductor devices.