Wet chemical etching process on as-deposited CdTe surface using nitric-phosphoric (NP) acid improved the efficiency of CdS/CdTe solar cells from 10.1% to 13.8%. Nitric-phosphoric (NP) acid solution etched native oxide (TeO2) layer and resolved excess cadmium on CdTe surface. After the heat treatment process activated the CdCl2, CdO layer which was believed to be a diffusion barrier of chlorine did not grow on the etched CdTe surface and new (V-Cd(2-)-2Cl(Te)(1+))(0) complexes was located at E-V + 0.045 eV. New (V-Cd(2-)-2Cl(Te)(1+))(0) complexes acted as a shallow acceptors and induced to improve V-oc and J(sc). The surface of CdTe thin film has been studied using Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and low temperature Photoluminescence (PL). (C) 2012 Elsevier B.V. All rights reserved.