Ruthenium polypyridyl TG6 dye for the sensitization of nanoparticle and nanocrystallite spherical aggregate photoelectrodes.

A ruthenium polypyridyl dye containing a hexasulfanyl-styryl modified bipyridyl group as ancillary ligand, coded TG6, is investigated as a sensitizer for ZnO-based dye-sensitized solar cells (DSSCs). The advantages of this dye are a broad wavelength absorption spectrum, a large loading in ZnO photoelectrodes, a significantly larger extinction coefficient compared to more classical Ru-polypyridyl dyes, and the formation of less agglomerate in the pores of the ZnO layers. TG6 has been used to sensitize ZnO nanorod particle layers of high structural quality and ZnO layers made of submicrometer spheres composed of aggregated nanocrystallites and that develop an internal surface area. The latter are highly light-scattering in the visible wavelength region but more difficult to sensitize correctly. The TG6 dye has been compared with the metal-free D149 dye and has been shown more efficient for photoconversion. The best performances have been obtained by combining TG6 with the nanorod layer, the optimal power conversion efficiency being measured at 5.30% in that case. The cells have been investigated by impedance spectroscopy over a large applied voltage range. We especially show that the submicrometer sphere layers exhibit lower conductivity and lower charge collection efficiency as compared to the nanorod particle ones.