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.

Electrodeposited nanoporous versus nanoparticulate ZnO films of similar roughness for dye-sensitized solar cell applications.

We present a comparative study of two different ZnO porous film morphologies for dye-sensitized solar cell (DSSC) fabrications. Nanoparticulate ZnO was prepared by the doctor-blade technique starting from a paste containing ZnO nanoparticles. Nanoporous ZnO films were grown by a soft template-assisted electrochemical growth technique. The film thicknesses were adjusted at similar roughness of about 300 in order to permit a worthy comparison. The effects on the cell performances of sensitization by dyes belonging to three different families, namely, xanthene (eosin Y) and indoline (D102, D131, D149 and D205) organic dyes as well as a ruthenium polypyridine complex (N719), have been investigated. The mesoporous electrodeposited matrix exhibits significant morphological changes upon the photoanode preparation, especially upon the dye sensitization, that yield to a dramatic change of the inner layer morphology and increase in the layer internal specific surface area. In the case of indoline dyes, better efficiencies were found with the electrodeposited ZnO porous matrixes compared to the nanoparticulate ones, in spite of significantly shorter electron lifetimes measured by impedance spectroscopy. The observation is interpreted in terms of much shorter transfer time in the oxide in the case of the electrodeposited ZnO films. Among the tested dyes, the D149 and D205 indoline organic dyes with a strong acceptor group were found the most efficient with the best cell over 4.6% of overall conversion efficiency.