The Mechanism of Iodine Reduction by TiO 2 Electrons and the Kinetics of Recombination in Dye-Sensitized Solar Cells

Electron transfer from TiO 2 to iodine/iodide electrolytes proceeds via reduction of either I 3 – or uncomplexed I 2 (free iodine), but which route predominates has not previously been determined. By measurement of the electron lifetime while independently varying free iodine or I 3 – concentrations, we find the lifetime is correlated with free-iodine concentration and independent of I 3 – concentration. This trend supports the hypothesis that electron recombination to the electrolyte occurs predominantly by iodine reduction rather than reduction of triiodide.