Fluorescence Properties of Dye Molecules Interacting with Nanoparticle Surface in Dye-Dispersing Titania Gels

摘要

The dye–titania interaction is very important for the electron injection process in dye-sensitized solar cells (DSSCs). For example, the steam treatment of a fluorescein-dispersing amorphous titania film remarkably improved the photoelectric conversion efficiency due not only to its crystallization but also to the dye–titanium surface complex formation. The titanium chelation of the carboxylate and carbonyl of the dye was promoted in the narrow spaces among the titania nanoparticles. Such interaction caused the ligand-to-metal charge transfer (LMCT) interaction. The complex formation enhanced the photocurrent due to improvement in the efficiency of the electron injection into the titania conduction band for the photoelectric conversion. A great degree of fluorescence quenching was observed in the steam-treated titania due to the electron injection from the dye into the titania. On the other hand, relative fluorescence quantum efficiency of fluorescein was enhanced in the titania gel films containing a small amount of silica due to the strong hydrogen bonding interaction between the TiOH groups on the titania surface and the carboxylate and carbonyl of the fluorescein species and a transformation from the anion to the highly fluorescent dianion species.