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 π 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 π 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.