A Comparison of the Behavior of Single Crystalline and Nanowire Array ZnO Photoanodes

The photoelectrochemical behavior of n-type ZnO nanowire arrays was compared to the behavior of single crystalline n-ZnO photoelectrodes in contact with either 0.50 M K₂SO₄(aq) at pH 6.0 or Fe­(CN)₄^3–/4–(aq). The use of a thin film of ZnO as a seed layer produced dense nanowire arrays in which the ZnO nanowires were preferentially oriented perpendicular to the substrate. The average diameter of the ZnO nanowires that were produced by two different growth conditions was ∼125 and ∼175 nm, respectively, with a nanowire length of ∼2–4 μm. Under simulated 1 Sun Air Mass 1.5 illumination conditions, the ZnO nanowire arrays exhibited open-circuit potentials, <i>E</i>_oc, and short-circuit photocurrent densities, <i>J</i>_sc, that were very close to the values observed from single crystal n-type ZnO photoanodes in contact with these same electrolytes. Device physics simulations were in accord with the experimentally observed behavior, indicating that, under certain combinations of materials properties and interface recombination velocities, the use of nanostructured light absorbers can provide an approach to efficient photoelectrochemical solar energy-conversion systems