The Mechanism of Iodine
Reduction by TiO<sub>2</sub> Electrons and the Kinetics of Recombination
in Dye-Sensitized Solar
Cells
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Abstract
Electron transfer from TiO<sub>2</sub> to iodine/iodide
electrolytes
proceeds via reduction of either I<sub>3</sub><sup>–</sup> or
uncomplexed I<sub>2</sub> (free iodine), but which route predominates
has not previously been determined. By measurement of the electron
lifetime while independently varying free iodine or I<sub>3</sub><sup>–</sup> concentrations, we find the lifetime is correlated
with free-iodine concentration and independent of I<sub>3</sub><sup>–</sup> concentration. This trend supports the hypothesis
that electron recombination to the electrolyte occurs predominantly
by iodine reduction rather than reduction of triiodide