CdS/CdSe quantum dot-sensitized solar cells (QDSCs) based on TiO2 nanoparticles were examined. TiO2 nanoparticles were coated with three different insulating oxide materials, Al2O3, MgO and BaTiO3, as a barrier layer to prevent recombination losses. In this study, a single and double coated barrier layer is fabricated to optimize the passivation effect. The optimized double coating structure increased the electron transport rate and electron lifetime and showed improved conversion efficiency. (C) 2013 Elsevier Ltd. All rights reserved.