In addition, the performance of piezoelectric-based NGs is strongly dependent on the structural and electrical properties of the piezoelectric materials used. A study of these properties and their dependence is very important to realize better NGs. One way to improve the properties of piezoelectric-based devices is by changing their morphology, e.g., microcantilevers , functionally graded materials , thin films [15,25-28], nanorods [10,29], and nanobelts . Nanofiber structures are significantly different from microscale or macroscale structures, particularly with regard to the high active areas of the former . The pattern of a nanofiber structure increases mechanical energy absorption in fiber-based NGs, making it higher than that in the case of nearly spherical particle-based NGs. Moreover, nanofibers can gradually distribute the mechanical force from one fiber to another over a long period, thereby resulting in a better effect for piezoelectric-based NGs. Nanofibers also possess several remarkable characteristics, such as high porosity, flexibility in surface functionality, and superior mechanical performance. Therefore, nanofiber structures are interesting to study, as they have many advantageous properties and can be produced using a simple low-cost electrospinning machine [16,17,31-34].