Large piezoelectricity in crosslinked ferroelectric polymers

Ferroelectric polymers exhibit numerous advantages for flexible and wearable electromechanical applications. However, their piezoelectric coefficient d33 remains relatively low while most previous approaches to improve d33 mainly focus on intramolecular engineering. Other than using intramolecular approaches, here we describe an intermolecular crosslinking strategy to achieve markedly enhanced d33 of −95.0 picocoulombs per newton in crosslinked ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) copolymers. First-principles calculations reveal that intermolecular crosslinking creates strong local conformational heterogeneity facilitating ease of bond rotation near the crosslinking sites, which leads to a flattened energy landscape, resulting in substantially improved d33 response. We show that crosslinking enabled by solution casting process enhances piezoelectric properties across a variety of crosslinking agents. Our work offers a facile platform for rational modulation of piezoelectricity of ferroelectric polymers, representing a crucial step towards large-scale manufacturing of lightweight, flexible, and scalable ferroelectric polymers for developing high-performance electromechanical devices. The d33 values of ferroelectric polymers are low in comparison to ceramics, such as perovskite oxides. Here, the authors report an intermolecular crosslinking strategy to improve the piezoelectricity of poly(vinylidene fluoride-co-trifluoroethylene) copolymers, achieving high d33 values.