Size Fractionation of Graphene Oxide via Solvent‐Mediated Consecutive Charge Manipulation and Investigation of the Size Effect as Hole Transporting Layer in Perovskite Solar Cells

Abstract Although intensive research for graphene oxide (GO) has been conducted, the broad size distribution of as‐synthesized GO flakes still remains a challenging issue since flake size has a direct impact on the material properties and related applications. Herein, we propose a facile and scalable approach for the size fractionation of GO flakes by manipulating the surface charge of GO with an organic solvent‐mediated aqueous solution. Both the experimental and simulation results confirm that the dispersion of GO flakes is notably influenced by the bond strength with solvent, which is attributed by the charge amount of oxygen in solvent molecule. From the understanding of the dispersion mechanism, an optimal solvent for the size fractionation of GO flakes was determined and GO flakes were successfully sorted into various size groups with a narrow distribution. The effect of size fractionation on the material property and related application was confirmed through various analyses. Our results could bring significant advances in producing two‐dimensional materials with reliable and reproducible material properties toward practical applications.