A photoelectrochemical cell (PEC) harnesses sunlight to produce hydrogen gas (H2) via water splitting. Silicon (Si) is abundant and widely used as a photovoltaic semiconductor material. Si has also been utilized as a photocathode in PEC owing to outstanding physical properties, including an optimal bandgap (Eg ≈ 1.1 eV) allowing for the absorption of a large portion of solar spectral irradiance, and the position of the conduction-band edge, which is higher than the proton reduction potential.
Recent attempts to improve the H2 evolution efficiency in PEC systems through the application of nanowires have aimed at utilizing superior antireflectance and polarization-insensitive light absorbance over broad wavelengths, as well as the larger surface area of the nanostructures. Superior antireflectance of nanostructures was observed to greatly enhance photocurrent. In addition, the enlarged surface area reduced the external bias required to drive the water splitting reaction by a minimum of 1.23 V. The increase in surface recombination loss due to an increased surface area, however, leads to lower energy conversion efficiencies in comparison to the theoretically estimated value for Si nanowire based PEC systems. It is therefore of significant importance to design a novel nanostructure capable of minimizing recombination loss as well as light reflection, despite these typically being inversely proportional variables.