Constructing a full-space internal electric field in a hematite photoanode to facilitate photogenerated-carrier separation and transfer

Abstract

Hematite (α-Fe₂O₃) material has outstanding advantages in the photoelectrochemical water splitting (PEC-WS) field, while its generally low photogenerated-carrier separation (η_sep) and transfer (η_tran) efficiencies severely impede its further application. An internal electric field can significantly enhance η_sep and η_tran efficiencies, but the effective scope urgently needs to be expanded. This work innovatively implements gradient doping into an α-Fe₂O₃ film to achieve a direction-controlled and full-space internal electric field throughout the entire photoanode. The carrier-transport dynamics and density functional theory (DFT) calculations demonstrate that the direction of the internal electric field of an α-Fe₂O₃ photoanode with gradient-decreasing doping is consistent with that of the photoanode/electrolyte junction. The synergy effect between them can substantially enhance the photogenerated-carrier separation and transfer efficiency. Compared with the case of gradient-increasing doping, the α-Fe₂O₃ photoanode with gradient-decreasing doping exhibits the largest saturated photocurrent density and an enhancement of 40.7% (55.2%) for η_sep (η_tran) at 1.23 V_RHE under AM 1.5G illumination. This work provides a facile and general gradient doping strategy to expand the effective scope of an internal electric field for boosting the photoelectric conversion performance.