TiO2 compact layer for dye-sensitized SnO2 nanocrystalline thin film.

A TiO 2 compact layer was coated on fluorine-doped tin oxide (FTO) glass substrate prior to deposition of SnO 2 nanocrystalline thin film to suppress backflow of electrons from FTO to the SnO 2 nanocrystalline thin film. The resultant thin film was used as a photoelectrode to fabricate dye-sensitized solar cell. For comparison, a SnO 2 compact layer was also prepared to discuss the effect of the TiO 2 compact layer on the electron backflow process. Compared with the dye-sensitized SnO 2 nanocrystalline thin film solar cell without the compact layer, light-to-electric conversion efficiency for the solar cell with the TiO 2 compact layer was improved by 82.1% and it was even improved by 41.7% compared with the cell with the SnO 2 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 TiO 2 compact layer. Both recombination resistance at the photoelectrode/electrolyte interface and lifetime of electrons on the SnO 2 nanocrystalline thin film were increased due to introduction of the TiO 2 compact layer. Because the conduction band of TiO 2 is higher than that of SnO 2 , the TiO 2 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 SnO 2 thin film. [ABSTRACT FROM AUTHOR]