Molecular adjustment of the electronic properties of nanoporous electrodes in dye-sensitized solar cells

Molecular modification of dye-sensitized, mesoporous TiO₂ electrodes changes their electronic properties. We show that the open-circuit voltage (V_oc) of dye-sensitized solar cells varies linearly with the dipole moment of coadsorbed phosphonic, benzoic, and dicarboxylic acid derivatives. A similar dependence is observed for the short-circuit current density (I_sc). Photo voltage spectroscopy measurements show a shift of the signal onset as a function of dipole moment. We explain the dipole dependence of the V_oc in terms of a TiO₂ conduction band shift with respect to the redox potential of the electrolyte, which is partially followed by the energy level of the dye. The I_sc shift is explained by a dipole-dependent driving force for the electron current and a dipole-dependent recombination current.