Surface Characterization of Chemically Treated Cu(In, Ga)Se2 Thin Films

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Abstract
The surfaces of Cu-rich and stoichiometric (slightly [In, Ga]-rich) Cu(In, Ga)Se2 (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- x Se and Cu(In, Ga)3Se5 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- x Se impurity and the treatment in the NH3 solution removed Cu2- x Se only at the front surface. In the stoichiometric CIGS film, the NH3 treatment removed Cu(In, Ga)3Se5 from 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.