Aromatic amines as co-sensitizers in dye sensitized titania solar cells

Solar cells based on titania require the use of sensitizing dyes in order to make the absorption band coincident with the solar spectrum. The most successful sensitizing dyes are based on Ru-bipyridyls and are chosen for their absorption and redox characteristics. In addition to absorbing visible light, the sensitizing dye injects an electron from its excited state into the band gap of the titania. The injected electron must be conducted through the titania to an electrode upon which the titania is coated. One of the energy wasting pathways available to the injected electron is back transfer to an oxidized dye species on the surface of the titania. We have discovered a simple means of alleviating this energy wasting pathway by anchoring aromatic amines, i.e., co-sensitizers, at low concentration along with the Ru-based bipyridyl sensitizing dye to the surface of titania nanoparticles. Our results indicate that there is a significant increase in cell efficiency (similar to 15% at AM 1.5, area greater than or equal to 1 cm(2)) primarily due to an increase in current when these species are present on the surface in combination with the dyes. We will report our preliminary results on a series of co-sensitizers, and we will compare these to literature findings which use similar compounds as either co-adsorbed species on titania or as substituents on the sensitizing dye molecule itself.