We have synthesized new room temperature ionic liquids and test them as new potential electrolytes for dye-sensitized nanocrystalline solar cells (DNSCs) of Gratzel type based on asymmetric tetraalkylphosphonium iodides. A systematic study on the conductivity behavior of BH3PI, iBH(3)PI, OH3PI and iBO(3)PI molten salts and the effect of the addition of low concentrations of iodine with and without 3-methoxypropionitrile is presented. Solar cells using iBH(3)PI-based electrolyte reached an overall light-to-electricity efficiency of 5.7% under moderate light intensity (27 000 lx) conditions and those results are compared to similar systems using alternative ionic liquids as electrolytes. (c) 2006 Elsevier B.V. All rights reserved.