XPS, UV–Vis, FTIR, and EXAFS Studies to Investigate the Binding Mechanism of N719 Dye onto Oxalic Acid Treated TiO2 and Its Implication on Photovoltaic Properties

The anchoring mechanism of N719 dye molecules on oxalic acid treated TiO2 (OA-TiO2) electrodes has been investigated using extended X-ray absorption fine structure (EXAFS) measurements, Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The FTIR spectroscopy of OA-TiO2 electrodes revealed that the oxalic acid dissociates at the TiO2 surface and binds through bidentate chelating and/or bidentate bridging. Analyses of EXAFS, FTIR, UV–vis, and XPS measurements of N719 dye loaded onto OA-TiO2 revealed that the binding of N719 molecules takes place via interaction between the Ru atom of the dye and O– of bidentate bridged oxalate ions at the TiO2 surface. This mechanism is quite different from the binding of N719 onto untreated TiO2 (WO-TiO2) surface, where −COOH and SCN groups of the dye directly bind to the TiO2 surface. The analyses of UV–vis data show that the amount of N719 dye loading onto OA-TiO2 surface is much higher than that onto the nati...