Hydrogen Evolution with Minimal Parasitic Light Absorption by Dense Co-P Catalyst Films on Structured p-Si Photocathodes

Planar and three-dimensionally structured p-Si devices, consisting of an electrodeposited Co-P catalyst on arrays of Si microwires or Si micropyramids, were used as photocathodes for solar-driven hydrogen evolution in 0.50 M H₂SO₄(aq) to assess the effects of electrode structuring on parasitic absorption by the catalyst. Without the use of an emitter layer, p-Si/Co-P microwire arrays produced a photocurrent density of -10 mA cm^-2 at potentials that were 130 mV more positive than those of optimized planar p-Si/Co-P devices. Champion p-Si/Co-P microwire array devices exhibited ideal regenerative cell solar-to-hydrogen efficiencies of >2.5% and were primarily limited by the photovoltage of the p-Si/Co-P junction. The vertical sidewalls of the Si microwire photoelectrodes thus minimized effects due to parasitic absorption at high loadings of catalyst for device structures with or without emitters.