Nearly Total Solar Absorption in Ultrathin Nanostructured Iron Oxide for Efficient Photoelectrochemical Water Splitting

We demonstrate using first-principles full-field electromagnetic simulations that nearly total above-band-gap solar absorption can be achieved in ultra-thin-film iron oxide photoanodes for water splitting applications. In our designed structure, all regions of iron oxide are away from the interface between iron oxide and water by a distance of less than the hole diffusion length, which is assumed to be 20 nm in our simulation. The absorption in our structure corresponds to a photocurrent density of 12.5 mA/cm2 if one assumes an air mass 1.5 solar spectrum and a unity absorbed photon-to-current efficiency. Our photon management strategy eliminates the trade-off between optical absorption and carrier collection as commonly found in conventional designs and is generally applicable to photoelectrochemical cells.