Study of Electrical and Mechanical Properties of PVDF-TrFE/KNN Composite Film with Flexible Energy Harvesting Application

In this work, a lead-free piezoelectric composite material comprising sodium potassium niobate (KNN) sol in an organic piezoelectric polymer (PVDF-TrFE) has been developed. The composite material can be deposited at low temperatures and is compatible with polymeric substrates. The piezoelectric coefficient has a maximum d33 value of 110 pm/V. This is superior to the piezoelectric coefficient for PVDF d33 = 28 pm/V, and most known lead-free piezocomposites that utilize PVDF. The controlled deposition of a thick (>1 μm) layer using spin coating can be easily achieved. The films are crack- and pinhole-free and require low-temperature processing. The introduction of the KNN sol in PVDF-TrFE improved the remnant polarization, dielectric constant, and piezoelectric coefficient of the resulting composite. Additionally, a tape-lift-off method for easily patterning these composite films has been developed, enabling the material to be utilized in micron-level devices. We demonstrate the piezoelectric properties of this composite by fabricating a flexible energy harvesting device that generates (Voc = 2.2 V) when compared to a PVDF-TrFE-based device (Voc = 0.05 V) for the same stimulation.