Effect of sensitizer structure and TiO2 protonation on charge generation in dye-sensitized solar cells

We report a joint theoretical and experimental investigation on the effect of TiO2 protonation on the interfacial electronic coupling and injection rates in organic dyesensitized solar cells (DSCs). We model the electronic structure of different organic dyesensitized TiO2 cluster models at different degrees of surface protonation and experimentally show the enhancement in the photocurrent generation upon the acidic treatment of the substrate. By merging theory and experiments, we elucidate the role of TiO2 protonation on the relative alignment and electronic coupling (injection rates) between the dye's lowest unoccupied molecular orbital and the semiconductor conduction band states, also in relation to the different electronic structure of the anchored dye (length of conjugation, conjugated vs not conjugated anchoring group). The photocurrent enhancement observed with TiO2 protonation is attributed to a combined effect of both red-shifted absorption of the protonated TiO2 films and to an overall improvement in the interfacial charge generation