Theoretical study on two-dimensional MoS₂ piezoelectric nanogenerators

Recent experiments have demonstrated that nanogenerators fabricated using two-dimensional MoS₂ flakes may find potential applications in electromechanical sensing, wearable technology, pervasive computing, and implanted devices. In the present study, we theoretically examined the effect of the number of atomic layers in MoS₂ flakes on the nanogenerator output. Under a square-wave applied strain, MoS₂ flakes with an even number of atomic layers did not exhibit a piezoelectric output, owing to the presence of a projected inversion symmetry. On the other hand, for MoS₂ flakes with an odd number of layers, owing to the lack of inversion symmetry, piezoelectric output voltage and current were generated, and decreased with the increase of the number of layers. Furthermore, as MoS₂ flakes were only a few atoms thick, the capacitance of the MoS₂ nanogenerators was at least an order of magnitude smaller than that of the nanowire- and nanofilm-based nanogenerators, enabling the use of MoS₂ nanogenerators in high-frequency applications. Our results explain the experimental observations and provide guidance on optimizing and designing two-dimensional nanogenerators.