Stable hole doping of graphene for low electrical resistance and high optical transparency

Abstract

We report on the p doping of graphene with the polymer TFSA ((CF3SO2)2NH). Modification of graphene with TFSA decreases the graphene sheet resistanceby 70%. Through such modification, we report sheet resistance values as low as129 Ω, thus attaining values comparable to those of indium–tin oxide (ITO), while displayingsuperior environmental stability and preserving electrical properties over extended timescales. Electrical transport measurements reveal that, after doping, the carrier density ofholes increases, consistent with the acceptor nature of TFSA, and the mobility decreasesdue to enhanced short-range scattering. The Drude formula predicts that competitionbetween these two effects yields an overall increase in conductivity. We confirm changes inthe carrier density and Fermi level of graphene through changes in the Raman G and 2Dpeak positions. Doped graphene samples display high transmittance in the visible andnear-infrared spectrum, preserving graphene’s optical properties without any significantreduction in transparency, and are therefore superior to ITO films in the nearinfrared. The presented results allow integration of doped graphene sheets intooptoelectronics, solar cells, and thermoelectric solar cells as well as engineeringof the electrical characteristics of various devices by tuning the Fermi level ofgraphene.