Direct growth of hematite film on p+n-silicon micro-pyramid arrays for low-bias water splitting

Solar water splitting based on photoelectrochemical (PEC) cells has been intensively demonstrated to be promising for hydrogen energy , but it is usually difficult for one pure PEC system to achieve overall solar-driven water splitting. To solve this problem, integrating one PEC cell with one photovoltaic (PV) cell is widely employed, however, the preparation of an unabridged PV cell and the electrical connection between them are complicated. Herein, we directly synthesized hematite (α-Fe 2 O 3 ) film on the as-prepared p + n-Si micro-pyramid arrays with the modifications of SnO 2 interlayer and Co-Pi catalyst overlayer, and the turn-on potential achieved a substantial decrease, which is 0.34 V smaller than the Sn-doped hematite film grown on the FTO substrate (FTO/Sn@α-Fe 2 O 3 ). The influences of interlayer, overlayer and α-Fe 2 O 3 preparation conditions are systemically investigated. Besides, we comparatively studied the FTO/Sn@α-Fe 2 O 3 photoanode in tandem with the complete p + n-Si micro-pyramid PV cell, and observed the turn-on potential as low as 0.32 V vs. RHE. The performance improvement is ascribed to a combination of the additional photovoltage from the embedded p + n-Si junction, the enhancement both in optical absorption and surface area of α-Fe 2 O 3 film, and the promoted collection efficiency of photogenerated carriers from the interface and surface modifications. This work fills the gap of combining α-Fe 2 O 3 photoanode and p + n-Si junction with the aim of overall solar-driven water splitting, and provides a new route to simplify the PEC/PV tandem system.