Degradation mechanisms in a dye-sensitized solar cell studied by UV-VIS and IR spectroscopy

By deliberately causing degradation of components in a dye-sensitized solar cell we have studied failure mechanisms of such cells. The dye, bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bipyridine-4-carboxylic acid, 4'-carboxylate)ruthenium(II), adsorbed to a nanostructured TiO2 film was studied with UV-VIS and IR spectroscopy after being exposed to visual and ultra-violet radiation, increased temperature, air, electrolyte, and water in the electrolyte. The thiocyanate ion ligand is lost in air, at temperatures equal to and above 135 degreesC, in electrolyte and possibly upon UV irradiation. The loss of the SCN- ligand in air was accelerated under visual illumination. From working electrodes immersed in the electrolyte or in degraded complete solar cells it was observed that the absorption peak from the thiocyanate ion ligand at around 2100 cm(-1) had broadened, blue-shifted and decreased. One failure mechanism is thus that the thiocyanate ion ligand is lost from the dye together with the electrolyte. Together with water in the electrolyte (5 v%) the SCN- ligand is exchanged with H2O and/or OH-. The ligand exchange between SCN- and H2O/OH- was accelerated under visual illumination. (C) 2003 Published by Elsevier Ltd.