Screen-Printed Structures from a Highly Conductive Mildly Oxidized Graphene Suspension for Flexible Electronics

In this study, the screen-printed flexible humidity sensor and supercapacitor structures from a suspension of mildly oxidized graphene (MOG) was obtained. MOG suspension with a low atomic oxygen content (~20%) was synthesized by electrochemical exfoliation of natural graphite in an aqueous solution of ammonium sulfate. MOG films (average thickness 5 μm) with a surface resistance of 10(2)–10(3) kΩ/sq were obtained by screen printing on a flexible substrate. The thermal reduction of MOG films at 200 °C reduced the surface resistance to 1.5 kΩ/sq. The laser reduction with a 474 nm and 200 mW solid-state laser reduced the surface resistance to ~0.065 kΩ/sq. Various structures were screen-printed on a flexible substrate for a variety of flexible electronics applications. The structures representing a flat supercapacitor had an average specific capacitance of ~6 μF/cm(2). The tensile deformations occurring during bending reduced the capacitance by 40% at a bending radius of 2 mm. Humidity sensing structures with sensitivity of 9% were obtained.