We report fabrication and characterization of solar cells based on vapor-liquid-solid (VLS) grown silicon nanowires (NWs) that form core-shell radial p-n junction structures. We observe efficiency enhancement due to the presence of the NWs that increase the light trapping within the device, while the use of gold as VLS catalyst results in increased carrier recombination within the wires. From the spectral efficiency data, we identify that the surface recombination effect becomes more significant in the large surface area NW cells. To remedy this issue we demonstrate the efficacy of a highly conformal Al(2)O(3) film grown by atomic layer deposition to serve as surface passivation layer. This work highlights the key issues confronted by NW-based solar cells grown by VLS technique. (C) 2009 Elsevier B.V. All rights reserved.