Characteristics of photoelectrochemical cells with iron oxide/n-Si heterojunction photoanodes

The iron oxide/n-Si heterojunction electrode was studied as a photoanode for a regenerative photoelectrochemical (PEC) cell. The influence of modifying the top layer of the electrode with Pd or RuO₂ was investigated. The photocurrent at the heterojunction electrode was produced by the holes which were photo-excited in both iron oxide and n-Si. The addition of Pd or RuO₂ on the heterojunction electrode surface enhanced the optical-to-electrical conversion efficiency. The efficiencies for a stable working PEC cell were found to be 1.34% and 1.60% for a Pd-and a RuO₂-modified electrode, respectively. This was measured in a 0.2 M KOH solution containing 0.2 M K₄[Fe(CN)₆] and 0.01 M K₃[Fe(CN)₆ at a xenon lamp intensity of 55 mW cm^-2. The use of iron oxide made the photoanode highly stable, as compared to an electrode such as RuO₂/n-Si. From a constant open-circuit voltage independent of the redox potential in 0.2 M KOH, it was concluded that Fermi level pinning occurs at the interface.