A high-performance flexible piezoelectric energy harvester based on lead-free (Na₀.₅Bi₀.₅)TiO₃-BaTiO₃ piezoelectric nanofibers

Recently wearable energy harvesters have attracted great attention due to their vital importance in portable energy-harvesting and personal electronics. Here we report a high-performance flexible piezoelectric energy harvester based on superior environmentally friendly 0.93(Na_0.5Bi_0.5)TiO₃-0.07BaTiO₃ (NBT-0.07BT) nanofibers. High-quality lead-free NBT-0.07BT fibers were synthesized by a sol-gel based electrospinning method. X-ray diffraction (XRD), scanning electron microscopy (SEM), piezoresponse force microscopy (PFM), and high-resolution transmission electron microscopy (HRTEM) were utilized to characterize the morphologies, phase structures, domain structures, and local piezoelectric response. The NBT-0.07BT nanofibers, which were located at the morphotropic phase boundary (MPB), exhibited a pure perovskite structure and superior local piezoelectric response (the effective normalized strain constant d_33,eff reached up to ∼109 pm V^-1 for single NBT-0.07BT nanofibers). The flexible piezoelectric energy harvester based on the NBT-0.07BT nanofibers exhibited a high peak voltage output of ∼30 V under 1 MΩ load resistance when applying a dynamic load using a finger and the short-circuit peak current reached ∼80 nA. Upon periodic mechanical impact, electrical energy was repeatedly generated from the device to power a commercial light-emitting diode. The advantages of small size, ease of processing, high flexibility, and environmental friendliness make this lead-free piezoelectric device quite promising for application in portable electronics.