Influence of annealing temperature on the existence of polar domain in uniaxially stretched polyvinylidene-co-hexafluoropropylene for energy harvesting applications

The structural and electroactive properties of the as-prepared random copolymer polyvinylidene-co-hexafluoropropylene thin film are explored as a function of thermal treatment at various temperature regions. The thermal treatment of the polymer thin film not only changes the structural conformations that is very natural but establishes a polar domain in the non-polar α-phase. Here, we discover an anomalous temperature-dependent crossover behavior from the non-polar α-phase to an appreciable enhancement in ferroelectric and piezoelectric responses. The maximum unipolar strain ( S m a x = − 5.01 % ), an ultrahigh value of normalized piezoelectric coefficient ( d 33 ∗ = − 556 pm / V ), high electromechanical coupling factor ( K p = 0.78 ) factor including the high dielectric constant ( ϵ ′ = 23 at 100 Hz ) at a relatively low electric field of 900 kV/cm may, therefore, be an effect of the established polar domain for the sample annealed at 105 °C. The direct piezoelectric charge coefficient (d33), a key factor for the performance of a prepared polymer thin film system as an energy harvester, lies in the range of − 10 ± 2 pC / N. Also, the annealed sample exhibited a persistent polarization after several cumulative cycles of applied stress.