Deceleration of dye cation reduction kinetics by adding alkyl chains to the [pi]-conjugated linker of dye molecules

To retard charge recombination between the injected electrons in TiO sub(2) and acceptor species in the electrolyte solution in dye-sensitized solar cells (DSSCs), alkyl chains have been introduced to dye molecules. To examine the effect of the alkyl chains on the dye cation reduction kinetics, we measured the transient absorption of the cationic state of dyes with and without alkyl chains in DSSCs and found that the reduction kinetics with alkyl chains slowed down for both injected electrons in TiO sub(2) and I-. The slower back electron transfer was interpreted with the slower hopping rate of the holes among the dyes on the TiO sub(2) surface, whereas the slower reduction by I- was probably a result of the blocking effect against the approach of I- to the dye molecules.