Inkjet-printed graphene electronics

Inkjet printing is a promising technique for printing of electronic materials and devices over large areas on flexible substrates. Inkjet printing is a versatile approach involving a limited number of steps with the ability to deposit controlled amounts of material. The development of inks for inkjet printing can be tailored to optimize the properties of the printed films and structures, and are additionally versatile in that virtually any nanomaterial composition can be incorporated as long as the nanostructure size is sufficiently small that the inkjet nozzle does not become clogged. The rule of thumb is nanostructure feature sizes ~1/50 the diameter of the nozzle. Solution dispersed nanostructures are being investigated as a means to incorporate semiconducting materials in printed thin films for electronic structures and devices. In the case of printed thin-film transistors (TFTs), the charge carrier mobility is much lower than that possible using crystalline silicon, typically on the order of 0.1-1.0 cm²/V-sec. One way to increase the carrier mobility of solution based printed TFTs is to utilize nanostructured materials having superior electronic transport properties, such as graphene or carbon nanotubes. The process described below describes the ink formulation and method for inkjet printed graphene films having charge carrier mobility up to 50 cm²/V-sec. Liquid phase exfoliation (LPE) is ideally suited to produce printable inks. LPE was achieved through sonication of graphite oxide following the Hummers method. By dispersing the graphene in N-Methyl-2-pyrrolidone (NMP) and using low power ultrasonication steps, the electronic properties of the graphene nanostructures are preserved by introducing less defects. Furthermore, the use of NMP provides a means to optimize the properties of of the ink for the inkjet deposition parameters.