The influence of alkylpyridines additive to an I-/I-3(-) redox electrolyte in acetonitrile on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2'-bipyridine-4-carboxylic acid, 4'-carboxylate)ruthenium(II) dye-sensitized TiO2 solar cell was studied. I-V measurements were performed using more than 30 different alkylpyridines. The alkylpyridine additives showed a significant influence on the performance of the cell. All the additives decreased the short-circuit photocurrent (J(sc)),ut most of the alkylpyridines increased the open-circuit photovoltage (V-oc) and fill factor (ff) of the solar cell. The results of the molecular orbital calculations suggest that the dipole moment of the alkylpyridine molecules correlate with the Jsc of the cell. These results also suggest that both the size and ionization energy of pyridines correlate with the V-oc of the cell. Under AM 1.5 (100 mW/cm(2)), the highest solar energy conversion efficiency (eta) of 7.6% was achieved by using 2-propylpyridine as an additive, which was more effective than the previously reported additive, 4-t-butylpyridine. (C) 2003 Elsevier B.V. All rights reserved.