Role of Annealing with Electric Field Toward Improvement of Ferroelectric and Electroactive Properties of PVDF Copolymer and Terpolymer Thin Films

The present study elucidates the role of annealing with electric field on lamellar crystalline structure and molecular orientation of polymer chains in ferroelectric copolymer (P(VDF-TrFE)) and ferroelectric terpolymer (P(VDF-TrFE-CFE)) spin-coated thin films. The ferroelectric polymer thin films annealed under an electric field support the growth of nanostructure with an "edge-on" lamellar crystalline structure having in-plane molecular chain orientation. The poled P(VDF-TrFE) thin films have higher remnant polarization (P_r) ≈6.2 µC cm^-2 and saturation polarization (P_s) ≈8.2 µC cm^-2 at an applied electric field of 250 MV/m compared to unpoled thin films having P_r ≈4.7 and P_s ≈6.2 µC cm^-2. Also, poled P(VDF-TrFE) thin films show lower coercive field (E_c) ≈94 MV/m compared to an unpoled thin film having E_c ≈105 MV/m. Similarly, poled PVDF-TrFE-CFE thin film shows better ferroelectric properties having P_r ≈0.4 and P_s ≈5.7 µC cm^-2 at an applied electric field of 200 MV m^-1 compared to unpoled thin films having P_r ≈0.4 and P_s ≈4.1 µC cm^-2. The storage energy efficiency of unpoled and poled P(VDF-TrFE-CFE) thin films is measured to be ≈75% and 80%. Annealing of ferroelectric P(VDF-TrFE) polymer thin films under an electric field demonstrates improved ferroelectric and electroactive properties.