By deliberately causing degrdn. of components in a dye-sensitized solar cell the authors 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) [N 719 dye] , adsorbed onto a nanostructured TiO2 film was studied with UV-visible and IR spectroscopy after being exposed to visual and UV radiation, increased temp., air, electrolyte, and water in the electrolyte. The thiocyanate ion ligand is lost in air, at temps. equal to and >135°, in electrolyte and possibly upon UV irradn. 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 the absorption peak from the thiocyanate ion ligand at ∼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.