Graphene -Gold Electrodes for Flexible Nanogenerators Based on Porous Piezoelectric PVDF Films

In this work, we develop graphene-gold electrodes (GGEs) for flexible nanogenerators made of porous piezoelectric PVDF films. The bilayer electrode structure was conceived in order to avoid the short circuit between top and bottom electrodes produced through direct Au sputtering over the film surface. Gold was sputtered over chemical-vapor- deposition (CVD) grown graphene film, that was subsequently transferred onto a PVDF film. We analysed the morphology and electrical properties of GGEs with increasing Au thickness in order to optimize the electrode surface conductivity and to guarantee high flexibility. The piezoelectric coefficient $\mathrm{d}_{33}$ of PVDF films and GGE-topped PVDF films were investigated through Piezoresponse Force Microscopy (PFM). We observed that the obtained values of $\mathrm{d}_{33}$, with and without GGEs, are in agreement with each other. This result allows to directly correlate the nanoscale piezoelectric properties to macroscale piezoelectric properties. Furthermore, a flexible nanogenerator made by a PVDF film top- and bottom- contacted with the bilayer GGEs was measured using a commercial mini -shaker. The obtained results are in good agreement with the measured $\mathrm{d}_{33}$ of the uncontacted PVDF film, obtained through PFM.