Dye-sensitization of the TiO2 rutile (110) surface by perylene dyes: Quantum-chemical periodic B3LYP computations

The adsorption of perylene derivatives on the rutile TiO2(110) surface was studied by quantum-chemical periodic calculations employing the hybrid HF-DFT functional B3LYP. The perylene molecule, which is a possible constituent of dyes in dye-sensitized solar cells, was functionalized by attachment of phosphonic acid or carboxylic acid groups to permit anchoring to the metal oxide surface. The anchor groups were bound to the molecule directly or via different spacer groups, namely --CH2-, -CH2-CH2-, and -CH = CH-. The effects of the anchor and spacer groups on the adsorption geometry and energy, on the electronic structure of the dye-TiO2 interface, and on the electron transfer rates were investigated. The phosphonic acid anchor group was found to bind the perylene derivatives much more strongly to the surface than the carboxylic acid anchor group. The spacer groups were capable of significantly altering electron transfer rates across the dye-metal oxide interface, where the unsaturated groups permitted injection times in the low femtosecond regime

Li and Na Diffusion in TiO2 from Quantum Chemical Theory versus Electrochemical Experiment

Diffusion of Li and Na ions in TiO2, anatase, has been studied using theor. (quantum chem. ab initio periodic Hartree-Fock and a modified semiempirical INDO) as well as electrochem. (chronocoulometry) methods. On the basis of the theor. calcns., the geometry of equil. and transition states for the impurities as well as the cryst. framework are analyzed and discussed. The calcd. activation energies for Li+ and Na+ diffusion were found to be only slightly higher than 0.5 eV by both theor. methods. The agreement of either theor. method with the electrochem. expts., 0.60 and 0.52 eV for Li+ and Na+, resp., is also remarkably good

PES Studies of Ru(dcbpyH2)2(NCS)2 Adsorption on Nanostructured ZnO for Solar Cell Applications

The interaction between the dye cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothiocyanato) ruthenium(II), Ru(dcbpyH2)2(NCS)2, and nanostructured ZnO was investigated by photoelectron spectroscopy (PES) using synchrotron radiation. The results are compared with those of nanostructured TiO2 sensitized with the same dye, which to date is the most efficient system for dye-sensitized photoelectrochem. solar cells. When comparing the two metal oxides, differences in the surface mol. structure were obsd. both for low and high dye coverages, as seen by comparing the oxygen, nitrogen and sulfur signals. The origin of these differences is discussed in terms of substrate-induced dye aggregation and in variations in surface bonding geometries. The measurements also provide information concerning the energy matching between the orbitals of the dye and the ZnO valence band, which is of importance in photoinduced charge transfer