We have investigated the effect of annealing thin-film CdS/Cu(In,Ga)Se-2 (CIGS) on solar cell performance. CdS/CIGS/Mo and CdS deposited on glass substrates were annealed on a hot plate in an air environment. Both the transmittance of the CdS layer at short wavelength and the X-ray diffraction (XRD) intensity of its (200) H peak increased after annealing. The quantum efficiency of the fabricated solar cells with annealed CdS buffer layer was also enhanced at short wavelength. A CIGS solar cell with a CdS buffer annealed at 200 degrees C for 1 min showed an efficiency of 16.47% (J(sc) = 34.18 mA/cm(2), V-oc = 0.642 V and Fill Factor = 75.0%) which is higher than that of an un-annealed solar cell by about 0.6%. We believe that annealing increases the optical transmittance and eliminates recombination centers at the p-n junction. This leads to the improved performance of CIGS solar cells. (C) 2010 Elsevier B.V. All rights reserved.