N3-sensitized TiO2 films:: In situ proton exchange toward open-circuit photovoltage enhancement

Protons of N3, cis-bis(thiocyanato) bis(2,2'-bipyridyl-4,4'-dicarboxylic acid) ruthenium(II), were in situ exchanged on N-3-loaded TiO2 films with alkali-metal, tetrabutylammonium, and guanidinium cations. This simple strategy improved the open-circuit photovoltage (V-oc) significantly, resulting in enhancement of the power conversion efficiency by 10-25%. Electrochemical impedance spectra revealed that the in situ proton exchange of the N-3-loaded film suppressed charge recombination between injected electrons and I-3(-) ions in the electrolyte, which, together with the negative shift of the conduction band edge for TiO2, may account for the remarkably increased Voc upon proton exchange of N-3.