Influence of the iodine content on the photocurrent in dye-sensitized solar cells using liquid polyiodide

A liquid polyiodide, composed of 1-hexyl-3-methylimidazolium iodide and iodine without any solvent, was used as a redox mediator in cis-Ru (4,4'-dicalboxyl-2,2'-bipyridine)(2)(thiocyanato)(2)-sensitized porous TiO2 solar cells with varying iodine mole fractions. For iodine mole fractions below 0.5, short-circuit anodic photocurrents were observed. However, for iodine mole fractions above 0.5, short-circuit cathodic photocurrents were observed. A mechanism of the photocurrents was discussed, and it is shown that a high concentration of I-3(-) promotes the back reaction of electrons with I-3(-) on transparent conducting oxide substrates under illumination, as well as acting as a filter of incident light into solar cells.