Unusual nanoscale piezoelectricity-driven high current generation from a self S-defect-neutralised few-layered MoS2 nanosheet-based flexible nanogenerator

摘要

We report the fabrication of a high-performance flexible piezoelectric nanogenerator based on S-defect-neutralised few-layered molybdenum disulphide (MoS2) nanosheets. High-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy confirmed the number of stacked layers in the MoS2 sheets to be 3–5. The defect, electronic and chemical states of the as-grown MoS2 nanosheets were investigated by X-ray photoelectron spectroscopy (XPS). An as-fabricated MoS2 nanogenerator with a CNT electrode generates an excellent high output voltage of 22 V and a record-high output current density of 9.00 μA cm−2 under a small vertical compressive force of 1.5 kgf. The piezoelectric charge coefficient of the 2D MoS2 nanosheets was investigated using piezoelectric force microscopy (PFM), and a very high piezoelectric charge coefficient (d33) of 120 pm V−1 was obtained. The energy conversion efficiency of the device was about 30%. Moreover, the MoS2 nanosheets show a high dielectric constant of about 2649 at low frequency. The results suggest that the absence of S-defects can reduce the free charge carrier and screening effect, resulting in a high output voltage and current density. The performance of the nanogenerator is discussed in terms of its high d33, high dielectric constant, the crystalline mixed phase of MoS2 and the electronic state of the MoS2 nanosheets.