Core-shell nanoporous electrode for dye sensitized solar cells: the effect of shell characteristics on the electronic properties of the electrode

Nanoporous TiO2 electrodes coated with a thin layer of various wide band gap materials were tested in dye sensitized solar cells (DSSCs). Using Nb2O5, ZnO, SrTiO3, ZrO2, Al2O3 and SnO2 as shell materials, we find that the mechanism by which the shell affects the electrode properties depends on the coating material. In the exceptional case of Nb2O5, the coating forms a surface energy barrier, which slows the recombination reactions. The other shell materials each form a surface dipole layer that shifts the conduction band potential of the core TiO2. The shift direction and magnitude depend on the dipole parameters which are induced by the properties of the two materials at the core-shell interface. The results show that either the shell acidity or the electron affinity of the shell are the shift controlling parameters, although the former seems more likely. This new toot for the modification of the electronic properties of the nanoporous electrodes allows for optimization towards a wide range of applications. (C) 2004 Elsevier B.V. All rights reserved.