A review of flexible lead-free piezoelectric energy harvester

Piezoelectric nanogenerator has emerged as a promising power generation device that converts mechanical energy into electrical energy. Flexible and stretchable piezoelectric energy harvesters can detect low frequencies like heartbeat, footsteps, ambient noise, and airflow, which is promising for further application. Thus, the development of a lead-free piezoelectric nanogenerator is required owing to its less toxic nature. One-dimensional ZnO (nanowire and nanorods) and perovskite-based materials (BaTiO₃ and BiFeO₃) have been widely investigated for piezoelectric nanogenerators because of their excellent piezoelectric properties and environmental friendliness. Hitherto, various electrodes, substrates, nanostructures, and polymers have been utilized to improve the efficiency of piezoelectric devices. In this review, we discuss the state-of-the-art achievements, stretchable piezoelectric nanowire, nanocomposite nanogenerators, and future possibilities of lead-free flexible energy harvesting devices.