Wafer-Scale Si-Based Metal−Insulator−Semiconductor Photoanodes for Water Oxidation Fabricated Using Thin Film Reactions and Multiple-layer Electrodeposited Catalysts

Solar-driven photoelectrochemical (PEC) water
splitting offers a promising and environmentally friendly route for
the conversion of renewable solar energy to hydrogen gas. A
crystalline Si absorber is especially attractive due to its moderate
bandgap, high charge mobility, long carrier diffusion length, costeffectiveness,
and scalability in manufacturing. To improve the
stability of Si-based PEC cells in operation, metal−insulator−
semiconductor (MIS) structures have been widely employed. In
this work, we employ simple and highly scalable processes to
fabricate high-performance, extremely stable Si-based MIS photoanodes,
and demonstrate their application to the fabrication of
wafer-scale photoanodes. Localized conduction paths formed via an
Al/SiO2 thin-film reaction enable low-resistance charge extraction
even through thick insulating layers, yielding photoanodes with excellent stability. To improve the efficiency, we demonstrate a twostep
Ni/NiFe electrodeposition process to create efficient oxygen evolution reaction catalysts. The Ni/NiFe catalyst allows for a high
Schottky barrier between Si and Ni, lowering the photoanode onset potential, while the NiFe surface layer improves the catalytic
performance. An unassisted solar-driven water splitting system incorporating a wafer-scale photoanode and monocrystalline Si solar
cells is demonstrated and yields a solar-to-hydrogen conversion efficiency of 6.9% under simulated AM 1.5G sunlight illumination.