Phase Separation and Low-pH Exposure Driven Self-Poled PVDF for Piezoelectric Energy Harvesters and Self-Powered IoT Sensors

Herein, we have solution-processed PVDF films crystallized into a polar β phase via electrostatic interaction with a polar solvent and its controlled demixing in a nonsolvent bath. Subsequently, the self-polarization alignment is ascertained on the treatment of these films in a low-pH aqueous solution. The combined X-ray diffraction, FTIR spectroscopy, and piezoelectric force microscopy (PFM) results revealed electroactive phases and an unseen polarization locking in these films. The out-of-plane cantilever deflection on application of a series of DC bias voltages implies a self-aligned property in these prepared films. The developed piezoelectric generator is shown to generate rms voltage, rms current, and power density of 4 V, 0.16 μA, and 100 μW cm –3, respectively, on application of a force as low as 1 N. The harvester showed charging of a range of capacitors, with a 10 μF capacitor reaching 1.0 V in less than 100 s. Further, on placing a 2.2 μF capacitor in series with a force-sensitive resistor (FSR) and a known resistor of 470 Ω, the human actuation force sensing in FSR is realized, which is validated with the voltage variation across the known resistor. This energy harvester can expand the use of low-powered IoT devices by enabling self-powered sensing, paving the way for future integration into commercial and smart technologies.