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 dramatically. 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 slight decreases in photovoltage and fill factor, resulting in overall solar conversion efficiency increases up to 45x for some dyes. The primary effect 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 the semidconductor to match the requirements of a specific dye, thus providing a versatile analytical tool for characterizing DSSCs while also enabling the use of new classes of sensitizing dyes. This letter describes the UV effect and summarizes the results of its application to a number of perylene-based sensitizers and two ruthenium bipyridyl sensitizers.