Solution Processing Route to Multifunctional Titania Thin Films: Highly Conductive and Photcatalytically Active Nb:TiO₂

Abstract

This paper reports the synthesis of highly conductive niobium doped titanium dioxide (Nb:TiO 2 ) films from the decomposition of Ti(OEt) 4 with dopant quantities of Nb(OEt) 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 2 films. For 5 at.% Nb in the films, the charge carrier concentration was 2 × 10 21 cm −3 with a mobility of 2 cm 2 V –1 s –1 . The corresponding sheet resistance is as low as 6.5 Ω sq –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 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 2 lattice. Computational methods also confirmed experimental results of both delocalized (Ti 4+ ) and localized polaronic states (Ti 3+ ) states. Additionally, the doped films also functioned as photocatalysts. Thus, Nb:TiO 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.