Density-functional theory study of the effects of atomic impurity on the band edges of monoclinic WO3

The effects of impurities in room-temperature monoclinic WO3 were studied by using the local density approximation to density-functional theory. Our main focus is on nitrogen impurity in WO3, where both substitutional and interstitial cases were considered. We have also considered transition-metal atom impurities and some codoping approaches in WO3. We find that, in general, band gap reduction was a common result due to the formation of impurity bands in the band gap. Also, the changes of band-edge positions, valence-band maxima and conduction-band minima, were found to depend on the electronic properties of the foreign atom and their concentration. Our results therefore provide guidance for making WO3 a suitable candidate for photoelectrodes for hydrogen generation by water splitting.