  Future generations of photoelectrodes for solar fuel generation must employ
inexpensive, earth-abundant absorber materials in order to provide a
large-scale source of clean energy. These materials tend to have poor
electrical transport properties and exhibit carrier diffusion lengths which are
significantly shorter than the absorption depth of light. As a result, many
photo-excited carriers are generated too far from a reactive surface, and
recombine instead of participating in solar-to-fuel-conversion. We demonstrate
that plasmonic resonances in metallic nanostructures and multi-layer
interference effects can be engineered to strongly concentrate sunlight close
to the electrode/liquid interface, precisely where the relevant reactions take
place. By comparing spectral features in the enhanced photocurrent spectra to
full-field electromagnetic simulations, the contribution of surface plasmon
excitations is verified. These results open the door to the optimization of a
wide variety of photochemical processes by leveraging the rapid advances in the
field of plasmonics.
