Large increases in photocurrents and solar conversion efficiencies by UV illumination of dye sensitized solar cells

Ultraviolet (UV) treatment of dye sensitized solar cells (DSSCs) containing tetra-ii-butylammonium iodide electrolyte increases photocurrents dramatic ally. The effect remains after cessation of UV illumination. Depending upon the photosensitizing dye, the increase in photocurrent can be as much as 2 orders of magnitude. The photocurrent increase more than compensates for s light decreases in photovoltage and fill factor, resulting in overall solar conversion efficiency increases up to 45x for some dyes. The primary effec t of the UV treatment appears to be a positive shift in the conduction band of the nanocrystalline titanium dioxide, which promotes electron injection from the dye. The dyes and the solar cells are both found to be stable to this treatment. This effect offers the ability to tune the properties of th e semidconductor to match the requirements of a specific dye, thus providin g a versatile analytical tool for characterizing DSSCs while also enabling the use of new classes of sensitizing dyes. This letter describes the UV ef fect and summarizes the results of its application to a number of perylene- based sensitizers and two ruthenium bipyridyl sensitizers.