Auxetic Laminar Composites Based on P(VDF-TrFE) for Enhanced Piezoelectric Performance in Flexible Energy Devices

The development of efficient, flexible, and sustainable energy-harvesting technologies is critical for powering self-sufficient wearable electronics, biomedical sensors, and remote IoT systems. In this study, we present an advanced auxetic laminar composite architecture that integrates piezoelectric polymer films—specifically P(VDF-TrFE) and P(VDF-TrFE-CTFE)—with re-entrant honeycomb substrates fabricated using a UV-curable resin. The negative Poisson’s ratio (NPR) behavior of auxetic structures was strategically employed to amplify in-plane mechanical strain in the active piezoelectric layers, enhancing voltage output under uniaxial loading. The electrospun nanofibers exhibited uniform, bead-free morphologies with preferential β-phase crystallinity, confirmed via SEM and wide-angle X-ray diffraction (WAXD). Finite element simulations revealed strong stress concentration at re-entrant hinges and vertical struts, with the degree of auxetic deformation increasing at larger monomer angles (55–65°) and thicker substrates. Digital image correlation (DIC) analysis confirmed consistent deformation behavior and validated simulated strain fields. Composite structures incorporating 5 mm-thick auxetic substrates and P(VDF-TrFE) films demonstrated superior mechanical strength, enhanced interfacial stress transfer, and significantly improved voltage response compared to P(VDF-TrFE-CTFE)-based systems. Experimental results showed that induced piezoelectric voltage increased nonlinearly with applied force and excitation frequency, with P(VDF-TrFE) achieving up to ~250% output enhancement. Simulated voltage outputs were in close agreement with experimental trends, supporting the design rationale. This work demonstrates a scalable, low-toxicity, and recyclable design for flexible piezoelectric harvesters using mechanical metamaterials. The integration of auxetic geometries with optimized piezoelectric polymers enables high sensitivity and tunable mechanical-electrical coupling, aligning with sustainable development goals. These findings provide valuable insights for designing next-generation flexible power sources for green energy applications.