Influence of benzimidazole additives in electrolytic solution on dye-sensitized solar cell performance

The influence of benzimidazole additives 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 with an I−/I3− redox electrolyte in acetonitrile was investigated by measuring the current–voltage characteristics of more than 20 different benzimidazole derivatives under AM 1.5 (100 mW/cm2). The benzimidazole additives tested had varying effects on the cell performance. Adding benzimidazole drastically enhanced the open-circuit photovoltage (Voc) and the fill factor (ff), but reduced the short-circuit photocurrent density (Jsc) of the solar cell. In order to determine the reasons for the additive effects on cell performance the physical and chemical properties of the benzimidazoles were computationally calculated. Consequently, the greater the calculated partial charge of the nitrogen atoms in position 3 of the benzimidazole groups, the larger the Voc, but the smaller the Jsc values. The Voc values also increased as the molecular size of the benzimidazole derivatives decreased. Moreover, the greater the absolute difference between the calculated dipole moment of the benzimidazole and acetonitrile, the larger the Jsc value. These results suggest that these properties of the benzimidazoles influenced the extent of interaction between the TiO2 electrode and electrolyte solvent, which changed the dye-sensitized solar cell performance.