Tapered and aperiodic silicon nanostructures with very low reflectance for solar hydrogen evolution

We introduce a facile method to generate silicon nanostructures with superior anti-reflectance (AR) properties. These nanostructures possess the ideal tapered structure and aperiodic distribution required for low reflectance over a broad range of wavelengths. Consideration of effective medium theories might explain the behavior between structure and reflectance, and suggest the advantage of aperiodicity in affording the material broadband AR properties. We then implemented these nanostructures as photocathodes to drive the hydrogen evolution reaction in AM 1.5 illumination. These nanostructures showed a significant improvement in photoelectrochemical performance over their planar counterpart, with the best performances corresponding to nanostructures which possessed AR properties matching the solar spectrum output.