2D Materials as Effective Cantilever Piezoelectric Nano Energy Harvesters

Two-dimensional (2D) layered piezoelectric nanomaterials are attractive for application in mechanical energy-harvesting devices. In this study, layered 2D nanosheets, h-BN and MX2 (M = Mo or W; X = S, Se, or Te), are deposited on a silicon substrate to form cantilever energy harvesters. Using density functional theory (DFT) and molecular dynamics (MD) calculations, the effect of the substrate for energy harvesting is studied. The substrate provides 2D layers with stable support while maintaining effective energy harvesting. MD results indicate that the electromechanical conversion energy has contributions from piezoelectricity and flexoelectricity, but the latter is negligible due to small strain gradients for bending-operated nanoharvesters. It is shown that the out-of-plane piezoelectric constants are substantially larger than their in-plane piezoelectric counterparts. The output power is calculated for a substrate-supported nanogenerator. This work provides an atomistic study of piezoelectricity and a new strategy to implement 2D materials in nano energy harvesters.