Benefiting from the advantages of low cost, light weight and mechanical flexibility, piezoelectric nanogenerators have the potential for application in renewable energy harvesting from various unexplored sources. Here, we report the demonstration of the record efficiency of flexible piezoelectric nanogenerators (PENG) using composites of polyvinylidene fluoride (PVDF) and chemically exfoliated tungsten disulfide (WS₂) nanosheets, which are found to be strongly photosensitive, making them attractive for self-powered optical devices. The presence of two-dimensional (2D) WS₂ nanosheets in the PVDF matrix plays a dual role in enhancing the nucleation of the electroactive β-phase as well as inducing strong photosensitivity in the nanocomposite. The PVDF-WS₂ composed flexible device is able to produce an enormously high output voltage of ∼116 V (for an impact of 105 kPa) and a piezoelectric energy conversion efficiency of ∼25.6%, which is the highest among the reported values for PVDF-2D material based self-poled piezoelectric nanogenerators. This self-poled piezo-phototronic device exhibits strain-dependent photocurrent at zero bias and exhibits a responsivity of 6.98 × 10⁻³ A W⁻¹ at 0.75% strain under the illumination of 410 nm. The fabricated PENG is also able to harvest energy from routine human activities (finger tapping, writing on paper, mouse clicking, etc.) and movement of human body parts. These results open up a new horizon in piezo-phototronic materials through the realization of photosensitive multifunctional PENGs, which can be scaled up for fabricating compact, high performance, portable and self-powered wearable electronic devices for smart sensor applications.

We report on the interrelation of optical emission of randomly oriented ZnO nanorod system with the carrier transport properties of Ag/ZnO nanorod-based rectifying junctions. The ZnO nanorods, exhibiting a hexagonal wurtzite phase, were fabricated by a cost-effective rapid thermal annealing process and at different annealing temperatures. The photoluminescence spectra of the as grown samples have revealed various Zn and O related native defects (e.g., vacancies, interstitials etc.) located at ∼400, 428, 491, and 535 nm. As evident from the I-V characteristic curves, though all the Ag/ZnO nanojunctions show Schottky behavior, the nanorods grown at a temperature of 550 °C and 650 °C are characterized by very large ideality factors of respective values 35.4 and 33.2, apart from displaying unusually high reverse currents. Whereas, the samples grown at 450 °C and 750 °C show usual rectifying nature having relatively lower ideality factors (18.4 and 12.2), along with low leakage-current under reverse biasing. The enhancement or suppression of the reverse currents can be attributed to the eventual lowering or raising of the Schottky barrier heights which result from the variation in the native defect states of various ZnO nanorod systems. Correlating optical events and electrical response through native defects would find scope in assessing figure of merit and sensitivity while making rectifying nanojunctions and single electron devices.