A partial electrolyte (PE) treatment was performed on the Cu(In,Ga)Se-2 (CIGS) absorber layer of thin,film solar cells to improve the quality of its interface with the cadmium sulfide (CdS) buffer layer. During the treatment, indium oxides and carbonates were removed and the CIGS surface was effectively doped by cadmium incorporation onto the surface. These effects were confirmed by scanning electron microscopy, x-ray and ultraviolet photoelectron spectroscopy. The surface cleaning and doping substantially improved the quality of the CdS/CIGS interface, which resulted in an order of magnitude lower dark current and the 3.0% enhanced power conversion efficiency of the PE-treated CIGS thin film solar cells, as compared with those of a conventional solar cell fabricated without PE-treatment. (C) 2017 Published by Elsevier B.V.