Surface charge transfer doping of graphene using a strong molecular dopant CN6-CP

Surface charge transfer doping of graphene plays an important role in graphene-based electronics due to its simplicity, high doping efficiency, and easy-controllability. Here, we demonstrate the effective surface charge transfer hole doping of graphene by using a strong p-type molecular dopant hexacyano-trimethylene-cyclopropane (CN6-CP). The CN6-CP exhibits a very high intrinsic work function of 6.37 eV, which facilitates remarkable electron transfer from graphene to CN6-CP as revealed by in situ photoelectron spectroscopy investigations. Consequently, hole accumulation appears in the graphene layer at the direct contact with CN6-CP. As evidenced by Hall effect measurements, the areal hole density of graphene significantly increased from 8.3 × 10¹² cm^?2 to 2.21 × 10¹³ cm^?2 upon 6 nm CN6-CP evaporation. The CN6-CP acceptor with strong p-doping effect has great implications for both graphene-based and organic electronics.