efficiency is dependent on three parameters [JSC, open-circuit
voltage (VOC), and fill factor]. Figure 8C plots JSC versus
roughness factor for nanoparticle cells (12-nm TiO2 particles
and 30- and 200-nm ZnO particles) and nanowire cells. The
nanowire cells show a nearly linear increase in JSC with an
increase in the roughness factor. The data almost lie directly
on the TiO2 nanoparticle data, which is significant because
transport is very efficient in thin TiO2 nanoparticle films.
This shows strong evidence for an equally high collection
efficiency for nanowire cells with wires as long as 25 µm.
Furthermore, the ZnO nanowire cells generate considerably
higher currents than either of the ZnO nanoparticle cells,
suggesting the superiority of the nanowire photoanode as a
charge collector. This nanowire architecture may also show
an improvement in the charge collection for polymerinorganic
solar cells. These devices are currently being tested
in our laboratory