Interfacial properties of the nanostructured dye-sensitized solid heterojunction TiO2/RuL2(NCS)(2)/CuI

The interfaces of the nanostructured dye-sensitized solid heterojunction TiO2/Ru-dye/CuI have been studied using photoelectron spectroscopy of core and valence levels, x-ray absorption spectroscopy and atomic force microscopy. A nanostructured anatase TiO2 film sensitized with RuL2(NCS)(2) [cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothio-cyanato)-ruthenium(II)] was prepared in a controlled way using a novel combined in-situ and ex-situ (Ar atmosphere) method. Onto this film CuI was deposited in-situ. The formation of the dye-CuI interface and the changes brought upon the dye-TiO2 interface could be monitored in a stepwise fashion. A direct interaction between the dye NCS groups and the CuI is evident in the core level photoelectron spectra. Concerning the energy matching of the valence electronic levels, the photoelectron spectra indicate that the dye HOMO overlaps in energy with the Cu 3d-I 5p hydrid states. The CuI grow in the form of particles, which at the initial stages displace the dye molecules causing dye-TiO2 bond breaking. Consequently, the very efficient charge injection channel provided by the dye-TiO2 carboxylic bonding is directly affected for a substantial part of the dye molecules. This may be of importance for the functional properties of such a heterojunction. (C) 2004 American Institute of Physics.