Multifunctional piezoelectric PVDF–Ba0.97Sr0.03TiO3 composite films for electrostatic energy storage, bio/force sensing, and optical applications

Abstract

Nowadays, the lives of individuals can be significantly improved by multipurpose piezo devices that can detect force or pressure, retain electrostatic energy, screen UV radiation, and produce power in response to changes in an individual's posture. To comply with the specifications, composite films of polyvinylidene fluoride–barium strontium titanate (PVDF–Ba_0.97Sr_0.03TiO₃) were fabricated with varying BST3 wt% values ranging from 10% to 50%. The ceramic filler was prepared by modifying the conventional solid-state reaction method, resulting in surface-adsorbed hydroxyl groups. BST3 at room temperature exhibited a piezoelectric charge coefficient of 122 pC N⁻¹. The beta phase content of the PVDF–BST3 composite films ranged from 75.8% to 79.4%. Up to a specific weight percentage (i.e., 40 wt%), their dielectric constant, recovered energy density (W_rec), total energy density (W_tot), piezo voltage, current, and power density increased and then decreased. A maximum W_rec of 101.2 mJ cm⁻³ and W_tot of 167.3 mJ cm⁻³ with 60.4% efficiency were accomplished for PVDF–BST3-40 at 250 kV cm⁻¹. A maximum V_P–P of 22.4 V was obtained for PVDF–BST3-40 across 0.1 MΩ resistance. Under a mechanical load of 50 N, the same film generated a voltage of 19.3 V, a current of 21 nA, and a power density of 11.6 μW cm⁻³. The voltage generated by hand tapping, fist beating, and elbow bending was measured to be 4, 7.5, and 3 V, respectively. The successful lighting up of six LEDs indicates that these composite films can operate as standalone devices. Additionally, their reduced optical bandgap with increasing BST3 content makes them suitable for UV-visible light shielding and photocatalysis.