Lead-Free Transparent Flexible Piezoelectric Nanogenerator for Self-Powered Wearable Electronic Sensors and Energy Harvesting through Rainwater

Most piezoelectric nanogenerators are based on bioincompatible materials, limiting their use in self-powered wearable applications. Addressing this, we report a high-performance, flexible, biocompatible, lead-free bismuth tungstate (Bi 2 WO 6 )-based piezoelectric nanogenerator. A facile, low-cost hydrothermal route is used to synthesize biconcave-shaped Bi 2 WO 6 nanoparticles. X-ray powder diffraction studies confirm its orthorhombic (pseudotetragonal) structure, while XRD studies prove its noncentrosymmetric ( Pca 2 1 ) space group is responsible for the origin of the piezoelectric property. Piezoelectric force microscopy (PFM) studies reveal a piezoelectric charge coefficient ( d 33 ) of 142.27 pm/V. A transparent Bi 2 WO 6:PDMS piezoelectric nanogenerator is fabricated using Bi 2 WO 6 nanoparticles embedded in a polydimethylsiloxane (PDMS) polymer matrix with platinum as a counter electrode and the device configuration of Pt-coated PET/(Bi 2 WO 6:PDMS)/ITO-coated PET. A stable, high output voltage and current density of 50 V and 0.6 μA/cm 2, respectively, are achieved by applying a low vertical compressive force (0.15 kgf, kilogram-force) without electric poling. This can be attributed to the high piezoelectric coefficient of Bi 2 WO 6 nanoparticles and the low surface energy of the highly flexible PDMS polymer. A fast response of 100 ms and energy conversion efficiency of 23.18% are obtained for the device, which is significantly higher than similar recent reports. In addition, the versatility of the robust nanogenerator is demonstrated by recording acoustic signals, energy harvesting from human body motion, utilizing it as a fast response smart sensor door, and energy harvesting from rainwater. The platform developed here proves its candidacy for numerous self-powered wearable biocompatible electronic applications.