Engineering the SiOx interfacial layer of Si-based metal-insulator-semiconductor junction for photoelectrochemical hydrogen production

Photoelectrochemical (PEC) water splitting provides a potential method to produce renewable hydrogen energy, but there is still plenty of room for improving the efficiency and stability of photoelectrodes. In this paper, we present a metal–insulator-semiconductor (MIS) structure based on p-Si that enables stable and efficient water splitting by engineering the interfacial insulating layer. The silicon oxide (SiO_x) film with appropriate thickness and low defects is regrown by a chemical oxidation process, which provides a high-quality insulating layer to passivate the p-Si. The carrier flux, barrier height and interfacial resistance of p-Si based MIS junction can be systematically tuned by controlling the thickness and quality of SiO_x layer. Under AM 1.5G illumination, the optimized p-Si/SiO_x/Ti/Pt photoelectrode shows an onset potential of 0.5 V vs. RHE, a maximum photocurrent of 28 mA/cm² and a high applied bias photon-to-current efficiency (ABPE) of 6 %. These results have significant implications for constructing MIS photoelectrodes towards effective water splitting.