Quantifying the influence of graphene film nanostructure on the macroscopic electrical conductivity

Graphene films have emerged as a promising nanostructured material class to exploit graphene's outstanding nanoscopic properties on the macroscale. Their potential applications include solar cells (Eda et al 2008 Appl. Phys. Lett. 92, 233305; Mullen et al 2008 Nano Lett. 8, 323-7), antennas (Zhang et al 2018 Electronics 7, 285; Song et al 2018 Carbon 130, 164-9), or electromagnetic interference shielding (Zhou et al 2017 Nanoscale 9, 18613-8; Wan et al 2017 Carbon 122, 74-81; Wang et al 2018 Small 14, 1704332), all of which require a high electrical conductivity. While an outstanding electrical conductivity is a key feature of pristine graphene monolayers, the transfer to the macroscale is challenging. Here, we combined theory and experiment to quantify the impact of specific structural graphene film properties. We synthesized graphene films with systematically varied flake sizes, studied their electrical conductivities, and found excellent agreement to simulations with a three-dimensional random resistor network model. In a further percolation-type study, we computed the critical share of non-conductive elements in a graphene film theta (c) = 10% where a substantial loss of electrical conductivity occurs. We prepared mixed films from graphene and graphene oxide to validate the threshold experimentally. In combination, experiments and simulations provide a coherent picture of how the graphene film microstructure is related to the macroscopic electrical conductivity (Rizzi et al 2018 ACS Appl. Mater. Interfaces 10 43088-94; Rizzi et al 2019 Comput. Mater. Sci. 161, 364-70). Our findings provide valuable insights for the production of highly conductive graphene-based macro-materials.