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

The influence of pyrimidine 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 studied. The current–voltage characteristics were measured for more than 10 different pyrimidine derivatives under AM 1.5 (100 mW/cm2). The pyrimidine additives tested had varying effects on the performance of the cell. The additives drastically enhanced the open-circuit photovoltage (Voc) and the solar energy conversion efficiency (η), but usually reduced the short circuit photocurrent density (Jsc) of the solar cell. Physical and chemical properties of the pyrimidines were computationally calculated in order to determine the reasons for the additive effects on cell performance. Consequently, the greater the calculated partial charge of the nitrogen atoms in the pyrimidine groups, the larger the Voc but the smaller the Jsc values. The Voc of the cell also increased as the ionization energy of the pyrimidine molecules decreased. Moreover, as the calculated dipole moment of the pyrimidine derivatives increased, the Jsc value was reduced, but the Voc value was enhanced. These results suggest that the electron donicity of pyrimidine additives influenced the interaction with TiO2 electrode and I−/I3− electrolyte, which lead to the changes in dye-sensitized solar cell performance.