Investigation on the photophysical processes in nanosized photocatalytic thin films using planar solid-state devices

摘要

The photophysical processes for three nanosized photocatalytic oxides, titanium dioxide (TiO2) thin film, tin dioxide (SnO2) thin film, and layered TiO2/SnO2 thin film, have been examined in planar solid-state devices. It is found that, for SnO2 thin film, the dissociation of the photogenerated excitons can take place both on the film surface and inside the film, while for TiO2 thin film, almost all excitons dissociate on the film surface. Such a difference is proposed to account for the higher photocatalytic activity of TiO2 over SnO2, since it is experimentally shown that the excitons dissociate in SnO2 thin film as efficiently as they do in TiO2 thin film. For layered TiO2/SnO2 thin film, when it is illuminated by a beam of UV light, it is suggested that there exists a local electrostatic field at the SnO2 side of the interface, mainly formed by those holes efficiently photogenerated and then localized in SnO2 thin film. The photo-induced local electrostatic field is believed to facilitate hole-electron separation on TiO2 thin film and therefore increase the photocatalytic activity of the layered thin film over single TiO2 thin film.