In this study, we demonstrate optical properties of multilayer system in an organic solar cell based on poly (3-hexylthiophene) (P3HT) and 6,6-phenyl C61-butyric acid methyl ester (PCBM) with semitransparent anode through thermal annealing effect. The optical absorption is enhanced via optimizing annealing treatment which further elevates near-field electric field amplitude. The electric field amplitude at the interface (active layer/semitransparent anode) is enhanced after thermal annealing corresponding to effective absorption near to semitransparent anode. Moreover, the thickness of the active layer is optimized via optical thin-film model for enhancing the organic solar cell efficiency. (C) 2010 Elsevier B.V. All rights reserved.