Free-Standing PVDF film for piezoelectric energy harvesting and sensing applications

Abstract

We report an effective way to enhance the electroactive beta-phase in free-standing polyvinylidene fluoride (PVDF) films by combining tape casting with hot-pressing. By varying systematically hot-pressing temperature, we optimized the crystalline phase composition and achieved a maximum beta-phase content of 69.25 % at 150 degrees C. Structural and phase changes were characterized through XRD, Raman spectroscopy, FTIR, and DSC, revealing a strong alpha-to-beta phase transformation. The optimized films showed enhanced dielectric permittivity, conductivity, and relaxation behaviour, driven by better molecular mobility and dipole alignment. Piezoelectric properties were evaluated through d33 and S-E hysteresis tests, reached a coefficient of 22.8 pm/V. Using the optimized film, we built a flexible piezoelectric energy harvester (PEH). The single-layer device delivered 5.6 mu W/cm3 under a 50 N load at 5 Hz, while a 4-layer design reached 47 mu W/cm3-nine times higher. The device also worked reliably with human body movements, showing strong potential for wearable electronics and selfpowered sensors.