Dye-sensitised solar cells (DSSC) based on commercial nanostructured zinc oxide combined with imidazolium-based room temperature ionic-liquid electrolytes are characterized. The electrolytes are based on a binary mixture of two ionic liquids, one of them used as source of iodide ions. The composition of this solvent-free electrolyte is optimized with respect to the concentration of iodine and iodide and the effect of additives such as lithium and tert-butylpyridine (TBP) on the photovoltaic performance and the recombination rate is analyzed and discussed. A maximum photoconversion efficiency of 3.4% at 1 sun illumination has been obtained for cells of 0.64cm(2) active area with the best performing compositions. Diffusion limitations due to slow transport processes are analyzed and discussed. (C) 2009 Elsevier B.V. All rights reserved.