  We demonstrate single layer graphene/n-Si Schottky junction solar cells that
under AM1.5 illumination exhibit a power conversion efficiency (PCE) of 8.6%.
This performance, achieved by doping the graphene with
bis(trifluoromethanesulfonyl)amide, exceeds the native(undoped) device
performance by a factor of 4.5 and the best previously reported PCE in similar
devices by a factor of nearly 6. Current-voltage, capacitance-voltage and
external quantum efficiency measurements show the enhancement to be due to the
doping induced shift in the graphene chemical potential which increases the
graphene carrier density (decreasing the cell series resistance) and increases
the built-in potential.
