Photomodulated Voltammetry of Iodide/Triiodide Redox Electrolytes and Its Relevance to Dye-Sensitized Solar Cells

Photomodulated voltammetry was used to determine the redox potentials of the diiodide radical (I-2(-center dot)) in water, acetonitrile, and 3-methoxypropionitrile. Iodide/triiodide redox electrolytes were exposed to modulated blue light, resulting in I-2(-center dot) generation. Using transparent fluorine-doped tinoxide (FTO) electrodes, two modulated photocurrent waves could be discerned in the voltammogram, from which the formal potentials for oxidation and reduction reactions of the diiodide radical were determined. E-0'(I-2(-center dot)/I-) was found to be +0.79 and +1.04 V versus NHE in acetonitrile and water, respectively. These values give guidelines for E-0'(D+/D) required for efficient regeneration of dyes used in dye-sensitized solar cells