Hybrid photovoltaic devices based on a blend of poly (3-hexylthiophene):(6,6)-phenyl C-61 butyric acid methyl ester and ZnO nanorod arrays (NRAs) with different densities have been investigated. Their surface morphology demonstrates that the interspaces of low-density ZnO nanorod arrays facilitate the complete infiltration of the polymer and close contact between NRAs, thus providing more double heterojunction interfaces and effective carriers transport paths than high-density NRAs. A remarkable improvement in power conversion efficiency from 2.80% to 4.07% has been achieved in the device with low-density ZnO NRAs relative to that with high-density ZnO NRAs. (C) 2011 Elsevier B.V. All rights reserved.