Parallel multi-stacked photoanodes of Sb-doped p–n homojunction hematite with near-theoretical solar conversion efficiency

Developing transparent and efficient photoanodes is a challenging but essential task in tandem photoelectrochemical cell for unassisted solar water splitting without an external bias. Here we report construction of p–n homojunction hematite photoanodes by hybrid microwave annealing-induced single antimony doping, which results in the gradually-increased valence states from the surface to the inside by the unique features of hybrid microwave annealing. The Sb-doped p–n homojunction hematite photoanode exhibits improved performance and displays a good transparency, achieving a stable photocurrent density of ~4.21 mA cm−2 at 1.23 VRHE under 100 mW cm−2 solar irradiation, which is comparable to the reported state-of-the-art hematite photoanodes. More importantly, a parallel-connected stack of six photoanodes of transparent p–n homojunction records a near-theoretical photocurrent density of ~10 mA cm–2 at 1.23 VRHE under standard photoelectrochemical water splitting conditions, which serves as a useful reference for hematite photoanodes and promises its practical application for unbiased photoelectrochemical water splitting. Developing efficient and transparent photoanodes for solar water splitting is crucial for advancing clean energy technologies. Here, the authors report Sb-doped p–n homojunction hematite photoanodes that achieve high transparency and a stable photocurrent density of 4.21 mA cm–2.