Exclusive electrical determination of high-resistance grain-boundaries in poly-graphene

Single layer graphene (SLG), with high optical transparency and electrical conductivity, may potentially be used as flexible transparent electrode in photovoltaics, photo detectors, and flat panel displays. While its optical transmittance exceeds 95% (significantly better than most traditional materials), its sheet resistance (ρ_poly-G) must be reduced below 10-20Ω/□ for viable replacement of present Transparent Conducting Oxides (TCOs) like Indium doped Tin Oxide (ITO). However, large scale CVD SLG is typically polycrystalline, consisting of many grains, with neighboring grains separated by high- and low-resistance grain boundaries (HGB and LGB), see Fig. 1 and 7. The HGBs severely limit the (percolating) electronic transport, so that ρ_poly-G>; 1000Ω/□. It is therefore important to determine the electronic nature and fraction of HGB to improve transport in polycrystalline SLG.