Solvent-Exchange-Assisted 3D Printing of Self-Polarized High β-PVDF for Advanced Piezoelectric Energy Harvesting

Three-dimensional (3D) printing technologies possess incom-parable advantages in fabricating 3D piezoelectric devices, enhancing the mechanical-to-electrical conversion efficiency. Among them, direct ink writing (DIW) holds great promise in constructing piezoelectric polymer devices as it enables self-polarization benefiting from the alignment of dipoles induced by the high pressure during the printing process. Besides, the electroactive phase of piezoelectric polymers is retained due to the operation is under ambient conditions. However, for the generally applied solvent-evaporation-assisted DIW technique, the architected structure suffers from drastic shrinkage and warpage in the final parts, which ultimately leads to a significant deviation from the programmed measure. In this work, for the first time, we develop a solvent-exchange-assisted DIW printing strategy to architect accurate and stable 3D PVDF PEH. This solvent exchange process in water not only enables the complete retaining of filament measure and generation of micropores to amplify the stain but also promotes the PVDF crystallization and formation of the beta-phase. Moreover, trace vitamin B2 is formulated into the ink, affording self-polarized high beta-phase content (95%) PVDF with good printability and optimal storage modulus to hold the 3D shapes. As a result, the 3D printed PVDF delivers an output voltage of 17.8 V, increased by 304% compared with device fabricated by solvent-evaporation-assisted DIW technique, and an impressive area output voltage density (11.04 V cm(-2)) which is twice that of the reported DIW printed PVDF PEH. This facile approach demonstrates a potential roadmap to high performance PEH through complex 3D enabled by the 3D technique.