Photovoltaic performances of polymer bulk-heterojunction solar cells (PSCs) with various sized (20, 35, 50, and 75 nm) Au nanoparticles (NPs) incorporated on indium tin oxide (ITO)-coated glass substrates are investigated in detail, wherein poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) blend serves as active layer and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as anode buffer layer on ITO. The optical and electrical properties of these devices incorporated with Au NPs with different space distributions in the interface of PEDOT:PSS buffer layer and P3HT:PCBM active layer are investigated. We find that, the optical property is improved as the Au NPs are large enough to penetrate into the active layer, while the performance of PSCs with small Au NPs can only benefit from the improved hole collection efficiency. Meanwhile, the exciton dissociation efficiency reduces remarkably as increasing the size of Au NPs. Finally, we demonstrated a maximum power conversion efficiency (PCE) improvement of similar to 23% in the PSCs by incorporating 35 nm Au NPs. (C) 2012 Elsevier B.V. All rights reserved.