Multifunctional P-Doped TiO₂ Films: A New Approach to Self-Cleaning, Transparent Conducting Oxide Materials

Abstract

Multifunctional P-doped TiO 2 thin films were synthesized by atmospheric pressure chemical vapor deposition (APCVD). This is the first example of P-doped TiO 2 films with both P 5+ and P 3– states, with the relative proportion being determined by synthesis conditions. This technique to control the oxidation state of the impurities presents a new approach to achieve films with both self-cleaning and TCO properties. The origin of electrical conductivity in these materials was correlated to the incorporation of P 5+ species, as suggested by Hall Effect probe measurements. The photocatalytic performance of the films was investigated using the model organic pollutant, stearic acid, with films containing predominately P 3– states found to be vastly inferior photocatalysts compared to undoped TiO 2 films. Transient absorption spectroscopy studies also showed that charge carrier concentrations increased by several orders of magnitude in films containing P 5+ species only, whereas photogenerated carrier lifetimes—and thus photocatalytic activity—were severely reduced upon incorporation of P 3– species. The results presented here provide important insights on the influence of dopant nature and location within a semiconductor structure. These new P-doped TiO 2 films are a breakthrough in the development of multifunctional advanced materials with tuned properties for a wide range of applications.