Coffee-Ring Structure from Dried Graphene Derivative Solutions: A Facile One-Step Fabrication Route for All Graphene-Based Transistors

We demonstrated a coffee-ring structure of graphene derivatives as a one-step solution fabrication route for graphene-based transistors. The key finding is that the coffee-ring structure formed after solvent evaporation of chemically modified graphene nanosheet solutions has an equivalent structure to all graphene-based transistors, the source/drain electrodes and semiconducting channel of which consisted monolithically of graphene nanosheets. These transistors have a thick stack of reduced graphene oxide at the edge of the coffee-ring structure, providing highly conductive thick graphite-like contact as the source and drain electrodes, and the thin film in the midsection of the coffee-ring pattern can simultaneously behave as the semiconducting channel. Here, we provide a holistic approach for achieving coffee-ring graphene-based transistors addressing the entire process flow starting with the coffee-ring structure formation from aqueous graphene oxide dispersion, proceeding through a rapid photoreduction using intensely pulsed white light, and finally a simple cutting of the edge line connections. The degree of graphene oxide reduction was precisely controlled by varying the irradiation energy of pulsed light, which allowed us to systematically investigate its effect on the transistor performances. We confirmed the feasibility of a coffee-ring graphene-based transistor using inkjet printing technique and using chemically reduced graphene oxide dispersions.