Solution Processing Route to Multifunctional Titania Thin Films: Highly Conductive and Photcatalytically Active Nb:TiO sub(2)

This paper reports the synthesis of highly conductive niobium doped titanium dioxide (Nb:TiO sub(2)) films from the decomposition of Ti(OEt) sub(4) with dopant quantities of Nb(OEt) sub(5) by aerosol-assisted chemical vapor deposition (AACVD). Doping Nb into the Ti sites results in n-type conductivity, as determined by Hall effect measurements. The doped films display significantly improved electrical properties compared to pristine TiO sub(2) films. For 5 at.% Nb in the films, the charge carrier concentration was 2 10 super(21) cm super(-3) with a mobility of 2 cm super(2) V super(-1) s super(-1) . The corresponding sheet resistance is as low as 6.5 Omega sq super(-1) making the films suitable candidates for transparent conducting oxide (TCO) materials. This is, to the best of our knowledge, the lowest reported sheet resistance for Nb:TiO sub(2) films synthesized by vapour deposition. The doped films are also blue in colour, with the intensity dependent on the Nb concentration in the films. A combination of synchrotron, laboratory and theoretical techniques confirmed niobium doping into the anatase TiO sub(2) lattice. Computational methods also confirmed experimental results of both delocalized (Ti super(4+)) and localized polaronic states (Ti super(3+)) states. Additionally, the doped films also functioned as photocatalysts. Thus, Nb:TiO sub(2) combines four functional properties (photocatalysis, electrical conductivity, optical transparency and blue colouration) within the same layer, making it a promising alternative to conventional TCO materials. Solution processing of Nb:TiO sub(2) has presented many challenges to the materials community. Nb:TiO sub(2) made by solution processing has been consigned to sensor/catalysis applications. Here, a solution route is presented to highly conductive and photocatalytically active Nb:TiO sub(2) films. A blue color is observed for the niobium doped films with XPS and computational methods showing a stable localized Ti super(3+) state at the anatase surface compared to the bulk.