Thiocyanate-free versus thiocyanate-containing dyes for TiO2-based dye-sensitized solar cells

The synthesis and properties of four new ruthenium dyes for TiO2-based dye-sensitized solar cells are presented. Bipyridine ligands with triarylamine or indoline moieties as donors, which differ both in the size of their conjugated systems and in their hydrophobicity, have been introduced into thiocyanate (SCN)-free and SCN-containing complexes. The structural changes affect the absorption and electrochemical properties. Extension of the conjugation leads to a shift in the absorption maximum to longer wavelengths, a broadening of the absorption spectra, and a decrease in the energy of the lowest unoccupied molecular orbital. The efficiency of TiO2-based solar cells that have been sensitized with the new complexes is mainly affected by the adsorption behavior of the dyes. The SCN-containing complex with the less-substituted or extended donor outperforms the other dyes.