Scalable, highly stable Si-based metal-insulator-semiconductor photoanodes for water oxidation fabricated using thin-film reactions and electrodeposition
Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water- splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efﬁciency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating MIS photoelectrodes. In this study, we demon- strate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin- ﬁlm reactions to create localized conduction paths through the insulator and electro- deposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p
+n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm
2 under simulated AM1.5G illumination. Moreover, in stability testing in 1 M KOH aqueous solution, a constant photocurrent density of ~22 mA/cm
2 is maintained at 1.3
V versus RHE for 7 days.