TiO2 compact layer for dye-sensitized SnO2 nanocrystalline thin film

A TiO2 compact layer was coated on fluorine-doped tin oxide (FTO) glass substrate prior to deposition of SnO2 nanocrystalline thin film to suppress backflow of electrons from FTO to the SnO2 nanocrystalline thin film. The resultant thin film was used as a photoelectrode to fabricate dye-sensitized solar cell. For comparison, a SnO2 compact layer was also prepared to discuss the effect of the TiO2 compact layer on the electron backflow process. Compared with the dye-sensitized SnO2 nanocrystalline thin film solar cell without the compact layer, light-to-electric conversion efficiency for the solar cell with the TiO2 compact layer was improved by 82.1% and it was even improved by 41.7% compared with the cell with the SnO2 compact layer. Electrochemical impedance spectroscopy and open-circuit voltage decay of dye-sensitized solar cells were measured to demonstrate the improvement mechanism due to the TiO2 compact layer. Both recombination resistance at the photoelectrode/electrolyte interface and lifetime of electrons on the SnO2 nanocrystalline thin film were increased due to introduction of the TiO2 compact layer. Because the conduction band of TiO2 is higher than that of SnO2, the TiO2 compact layer acts as not only a physical barrier to separate FTO substrate from electrolyte, thus suppressing recombination of electrons on FTO with the electrolyte, but also a potential barrier to effectively block the backflow of electrons from FTO substrate to the SnO2 thin film. (C) 2014 Elsevier Ltd. All rights reserved.