  The photoelectrochemical behavior of a planar 1 cm2 thick Ti-doped hematite
film deposited on F:SnO2 coated glass was studied with both front and back
illumination. Despite low quantum efficiency, photocurrent was observed upon
back illumination with low wavelengths, indicating that some photogenerated
holes are able to traverse at least 700 nm across the hematite film and
effectively oxidize water. This cannot be accounted for using the commonly
accepted hole collection length of hematite based on fitting to the Gartner
model. Furthermore, under back illumination, 450 nm excitation resulted in
increased photocurrent as compared to 530 nm excitation despite most of the
light being absorbed further away from the surface. These results demonstrate
that the photocurrent is strongly dependent on the optical excitation
wavelength, and related to both delocalized holes with long lifetime and
localized excitations rather than only being dependent on the proximity of the
absorption to the surface.
