Mechanically bent graphene as an effective piezoelectric nanogenerator

Recent density functional theory (DFT) calculations have demonstrated the potential of mechanically bent graphene as a piezoelectric energy harvesting material. We develop a two-dimensional (2D) model of hexagonal materials and demonstrate quantitatively the potential of a single layer of graphene to function as an effective piezoelectric nanogenerator. The piezoelectricity of graphene stems from a dynamically generated surface charge density proportional to the local curvature of the graphene layer, and the proportionality constant is found from DFT calculations on a single layer of bent graphene. By virtue of different tailored mechanical and electrical loadings, explored in this work, it is demonstrated that graphene can be as effective an energy harvester as a single flat layer of 2D MoS2, which is strongly piezoelectric due to its inversion-asymmetric unit cell. Demonstrations are carried out for graphene and MoS2 using a 2D finite element model to determine the generated voltage, current, and power density.