Orientation Dependence of Semiconductor Properties in Anatase TiO2 Polycrystalline Aggregates

We investigated the effects of the crystalline orientation of anatase titanium dioxide (TiO2) polycrystalline fine aggregates on semiconductor properties such as flatband potential and donor density, which affect performance in applications to dye-sensitized solar cells and photocatalysis. Aggregates with crystalline orientation were prepared through electrophoretic deposition in a strong magnetic field. Semiconductor properties were determined with Mott-Schottky plots obtained by an electrochemical impedance method. The flatband potential of the (001)-plane perpendicular to the electrode was most negative. That of the random orientation was varied rather widely while the average value was close to that of the (001)-plane perpendicular to the electrode. The open-circuit potential of the electrode corresponding to the Fermi level of TiO2 in contact with the electrolyte tended to depend on the crystalline orientation similar to the flatband potential. The distance between the open-circuit potential and the flatband potential was nearly constant regardless of plane orientation. These findings indicated that the flatband potential was controlled by Fermi-level pinning related to the surface state. Nominal donor density also depended on crystal orientation. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3208055] All rights reserved.