3D Printed Auxetic Structure‐Assisted Piezoelectric Energy Harvesting and Sensing

Abstract The fast development of wearable electronic systems requires a sustainable energy source that can harvest energy from the ambient environment and does not require frequent charging. Piezoelectric polymer films are a perfect candidate for fabricating piezoelectric nanogenerators (PENGs) to harvest mechanical energy from the environment due to their flexibility, good piezoelectricity, and environmental‐independent stable performance because of their inherent polarization. However, most of their applications are limited to the pressing mode energy harvesting that is based on the 3‐3‐direction piezoelectric effect due to the molecular polarization and nonstretchability. In this work, by 3D printing an auxetic structure on a polymer film‐based PENG, the bending deformation of the PENG can be transformed into the well‐controlled in‐plane stretching deformation, enabling the 3‐1‐direction piezoelectric effect. The synclastic effect of the auxetic structure is applied in flexible energy harvesting device for the first time, which makes the previously untapped bending deformation on a film a valuable device for energy harvesting and increases the bending output voltage of the PENG by 8.3 times. The auxetic structure‐assisted PENG is also demonstrated as a sensor to sense the bending angle and monitor the motion by mounting on different joints of the human body and soft robotic finger.