Effect of functional group on photochemical properties and photosensitization of TiO2 electrode sensitized by porphyrin derivatives

dA series of porphyrin derivatives containing carboxylic-, sulfo- and hydro- groups, 5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin (TCPP), 5,10,15,20-tetrakis(4-sulfophenyl)porphyrin (TSPP) and 5,10,15,20-tetraphenyl-porphyrin (TPP), were examined as sensitizers for porous nanocrystalline TiO2. The difference in the adsorption behavior on the TiO2 electrode surface was discussed. The interaction between the porphyrins and the TiO2 surface was determined and compared using UV-Vis spectra and X-ray photoelectron spectroscopy (XPS). The luminescence spectra of the porphyrins in DMF solution and adsorbed onto TiO2 electrodes were measured. The ionization potentials of the porphyrins in the solid state and adsorbed onto TiO2 electrodes were determined by a new approach using an apparatus for measuring the emission yield under atmospheric conditions. The importance of the binding states between the dye and TiO2 surface was discussed by comparison of the energy conversion efficiency in a dye-sensitized solar cell. The results indicate that the binding state and the amount of adsorbed dye are important factors affecting the properties of the dye-sensitized solar cell. (C) 2002 Elsevier Science B.V. All rights reserved.