in this work, we have used one dimensional simulation program called analysis of microelectronic and photonic structures (AMPS-ID) to design solar cells based on CuIn1-x ,GaxSe2 (CIGS) as the absorber material and study their device performances. Starting with a ZnO/In2S3/CIGS solar cell, an inverted surface layer and a grading space charge region (SCR) in the absorber were taken into account. The buffer layer used improves the open-circuit voltage (V-oc) without significantly sacrificing the short-circuit current density (J(sc)). Photovoltaic parameters were determined using current density-voltage (J-V) curve. Quantum efficiency (QE) is about 94% in the visible range. In2(S)S(3) buffer layer have shown to be a competitive alternative to devices with the CdS buffer. (C) 2006 Elsevier B.V. All rights reserved.