Computational investigation of the co-doping effect of sulphur and nitrogen on the electronics of CsTaWO₆

CsTaWO₆ is a typical AMWO₆-type compound and the photocatalysis of the pure and doped phases has been extensively studied experimentally. In this work, the electronic structures of sulphur (S) and nitrogen (N) co-doped CsTaWO₆ have been studied in the framework of density functional theory, in particular the S/N co-doping effect has been investigated. It is found that, (i) S/N co-dopants prefer to be separated; (ii) middle-gap states are introduced by N[sbnd] and S-dopant at the edges of valence band and conduction band; and (iii) Co-doping not only narrows the band gap, but also promotes the separation of photo-excited electrons and holes. Feature (iii) has been identified as a key reason why S/N co-doped CsTaWO₆ is more efficient in photocatalytic water-splitting. A general doping strategy has been further suggested: co-dopants which can dominate the frontier states and favour to be separated can offer excellent photocatalysis performance.