Double-hole-mediated coupling of anionic dopants in perovskite NaNbO3 for efficient solar water splitting

Doping is an effective strategy to improve the photocatalytic performances of semiconductor photocatalyst for water splitting. In this work, we perform extensive hybrid density functional calculations to investigate perovskite NaNbO3 with anionic monodoping with N, C, P, and S dopants as well as with (N + N), (C + S), and (N + P) codoping pairs. Theoretical results clearly reveal that the band structures of NaNbO3 can be effectively tailored by introducing double-hole-mediated coupling of anion-anion pairs. Compared with the monodoping cases, the anion-anion codoped NaNbO3 systems not only have substantially narrowed band gaps, but also can eliminate the unoccupied localized states appearing above the Fermi level, which are disastrous for photocatalysis as they may trap the photogenerated carriers. Optical absorption curves further convince that the codoped NaNbO3 can effectively harvest visible light. The band edge positions with respect to the redox potentials of water demonstrate that the (N + N) codoped NaNbO3 are desirable for efficient solar water splitting.