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