The effects of gold (Au) nanoparticles (NPs) with different morphologies (star, rod, sphere) incorporated into buffer layer, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS), of polymer-based organic solar cells (OSCs) were investigated. Solar cells having gold nanoparticles exhibited significant improvement in device efficiency relative to the reference device. The observed improvement is most likely due to the surface plasmon and enhanced light reflection and scattering properties of the Au NPs. The power conversion efficiency (PCE) is increased ca. 29% with Au nanostars, ca. 14% with Au nanorods and 11% with Au nanospheres compared to the device with no Au NP (reference device). Au nanostars provide the strongest contribution to the efficiency among all NP morphologies studied as they have large size, sharp features, and strongest localized surface plasmon resonance effect associate with their morphology. (C) 2013 Elsevier B.V. All rights reserved.