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 (alpha-Fe2O3) film on the as-prepared p(+)n-Si micro-pyramid arrays with the modifications of SnO2 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@alpha-Fe2O3). The influences of interlayer, overlayer and alpha-Fe2O3 preparation conditions are systemically investigated. Besides, we comparatively studied the FTO/Sn@alpha-Fe2O3 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 alpha-Fe2O3 film, and the promoted collection efficiency of photogenerated carriers from the interface and surface modifications. This work fills the gap of combining alpha-Fe2O3 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.

Automated summary

This study successfully lowers the turn-on potential for overall solar-driven water splitting by directly synthesizing hematite film on p(+)n-Si micro-pyramid arrays, along with modifications of interlayer and overlayer. The integration of alpha-Fe2O3 photoanode and p+n-Si junction is a promising approach to simplify the PEC/PV tandem system.