Efficient quantum dot-sensitized solar cells (QDSSCs) using nano-designed 3D nanostructures for use in both the counter electrode and the photoelectrode by combining 1D and 2D nanostructures were developed. New counter electrodes were fabricated by depositing noble metal nanoparticles onto a 3D carbon support composed of carbon nanotubes (CNTs) and reduced graphene oxide (RGO). The combination of CNTs and RGO in a 3D support maximized the surface area on which nanosized catalysts could be dispersed and facilitated mass transport of the redox couples. The high conductivities of carbon created a fast charge carrier transport channel that could supply electrons to the catalysts. Noble metal nanoparticles were immobilized on the 3D carbon support to act as highly active reaction sites for polysulfide reduction. The carbon support minimized the use of noble metals, and enhanced the electrode stability. A combination of 1D nanowires and 2D nanosheets was used to create 3D ZnO nanostructural scaffolds onto which quantum dot could be loaded for use in a photoelectrode. The nanowires provided direct electrical pathways to the bottom electrode and facilitated photogenerated charge collection. The nanosheet-structured branches provided an additional surface area for quantum dot loading. QDSSCs exhibited a remarkably high power conversion efficiency of 5.90% and enhanced photochemical stability. (C) 2014 The Electrochemical Society. All rights reserved.