Direct writing of graphene patterns and devices on graphene oxide films by inkjet reduction

Direct writing of graphene patterns and devices may significantly facilitate the application of graphene-based flexible electronics. In terms of scalability and cost efficiency, inkjet printing is very competitive over other existing directwriting methods. However, it has been challenging to obtain highly stable and clog-free graphene-based ink. Here, we report an alternative and highly efficient technique to directly print a reducing reagent on graphene oxide film to form conductive graphene patterns. By this "inkjet reduction" method, without using any other microfabrication technique, conductive graphene patterns and devices for various applications are obtained. The ionic nature of the reductant ink makes it clog-free and stable for continuous and large-area printing. The method shows self-limited reduction feature, which enables electrical conductivity of graphene patterns to be tuned within 5 orders of magnitude, reaching as high as 8, 000 S·m^–1. Furthermore, this method can be extended to produce noble metal/graphene composite patterns. The devices, including transistors, biosensors, and surfaceenhanced Raman scattering substrates, demonstrate excellent functionalities. This work provides a new strategy to prepare large-area graphene-based devices that is low-cost and highly efficient, promising to advance research on graphenebased flexible electronics.