The fill factor is attributed to the series and shunt
resistances. The series resistance is estimated to be
4.92 Ω/cm2. This series resistance arises from the bulk
and contact resistances, one reason for this being that
the graphite paste we used for the back-contacts has
a sheet resistance of 1,200 to 2,400 Ω/sq. A low shunt
resistance may have been caused by the contribution
of the incomplete isolation caused by the less than
satisfactory scribing of the intrinsic SnO2. Another
reason for the low shunt resistance is related to the
non-optimal growth of the CdS nanotubes.