Influence of nitrogen-containing heterocyclic additives in I−/I3− redox electrolytic solution on the performance of Ru-dye-sensitized nanocrystalline TiO2 solar cell

Abstract

The influence of nitrogen-containing heterocyclic additives on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized nanocrystalline TiO2 solar cell with an I−/I3− redox electrolyte in acetonitrile was studied. The current–voltage characteristics were measured under AM 1.5 (100mW/cm2) for 10 different five- and six-membered nitrogen-containing heterocyclic compounds. The heterocyclic additives tested had varying effects on the cell performance. Most of the additives enhanced the open-circuit photovoltage (Voc), fill factor (ff), and the solar energy conversion efficiency (η), but reduced the short circuit photocurrent density (Jsc). The physical and chemical properties of the nitrogen-containing heterocycles such as the partial charge, dipole moment, and ionization energy were computationally calculated in order to elucidate the reasons for the additive effects on the cell performance. The greater the lowest partial charge of the nitrogen atoms in the heterocyclic ring, the larger the Voc, but the smaller the Jsc values. The dark current at the bare TiO2 electrode without a dye coating decreased as the lowest partial charge of the nitrogen atoms increased. The Voc of the cell also increased as the ionization energy of the nitrogen-containing heterocyclic molecules decreased. These results suggest that the electron donicity of the nitrogen-containing heterocyclic additives influenced the interaction with the nanocrystalline TiO2 photoelectrode and the I−/I3− electrolyte, which altered the Ru-dye-sensitized solar cell performance.