Ion doping of graphene for high-efficiency heterojunction solar cells.

We demonstrated the p-type chemical doping by chlorine and nitrate anions to enhance the Schottky junction in the solar cell. Nitrate ions were found to be more effective for reducing the sheet resistance and enlarging the work function of graphene for effective charge separation and transport, and the efficiency was increased to 9.2% by a factor of 1.68 under AM 1.5 illumination.