Surface characterization of chemically treated Cu(In,Ga)Se-2 thin films

The surfaces of Cu-rich and stoichiometric (slightly [In, Ga]-rich) Cu(In, Ga)Se-2 (CIGS) thin films were investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At the surface of the Cu-rich and stoichiometric CIGS films, Cu2-xSe and Cu(In, Ga)(3)Se-5 exist, respectively. The films were treated using KCN and NH3 aqueous solutions. In the Cu-rich film, the treatment in the KCN solution completely eliminated the Cu2-xSe impurity and the treatment in the NH3 solution removed Cu2-xSe only at the front surface. In the stoichiometric CIGS film, the NH3 treatment removed Cu(In, Ga)(3)Se-5 hom the surface. The recombination of the carriers occurs more in the heterojunction of the CdS/NH3-treated CIGS system than in that of the CdS/as-deposited CIGS system.