The Mechanism of Iodine Reduction by TiO2 Electrons and the Kinetics of Recombination in Dye-Sensitized Solar Cells

Electron transfer from TiO2 to iodine/iodide electrolytes proceeds via reduction of either I3– or uncomplexed I2 (free iodine), but which route predominates has not previously been determined. By measurement of the electron lifetime while independently varying free iodine or I3– concentrations, we find the lifetime is correlated with free-iodine concentration and independent of I3– concentration. This trend supports the hypothesis that electron recombination to the electrolyte occurs predominantly by iodine reduction rather than reduction of triiodide.