A Photoelectron Spectroscopy Study of Z-907 Co-adsorbed with DPA on Nanostructured TiO2 Surfaces

• The surface electronic and molecular properties of mixed dye/coadsorbent sensitized TiO2 surfaces was investigated using photoelectron spectroscopy (PES). The sensitization of the TiO2 was performed using the ruthenium based dye cis-disothiocyanato-(2,2-bipyridyl-4,4-dicarboxylic acid)-(2,2-bipyridyl-4,4-dinonyl) ruthenium(II) (Z-907) together with different concentrations of the coadsorbent decylphosphonic acid (DPA). The investigation showed large variations in surface concentration of Z-907 and DPA depending on the dye/coadsorbent ratio in solution, but that the relative amounts at the surface and in solution substantially differ. Generally the DPA coadsorbents exchange with dye Z-907 molecule and trends in the surface concentration show that each dye molecule is replaced by six coadsorbent molecules. The co-adsorption of DPA induced changes in the S2p spectra, indicating changes in the dye surface interaction. Still, investigation of the frontier electronic structure in the dye sensitized TiO2 surfaces show that co-adsorbtion of DPA do not alter the energy level matching between the dye and the TiO2.

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