Transparent and Extremely Stretchable Piezoelectric Device for Sensors and Energy Harvesters

Piezoelectric devices have garnered significant interests due to their dual functionality as both sensors and energy harvesters, as well as the rapid development in Internet of Things (IoT) and artificial intelligence (AI). However, the fabrication of stretchable and transparent piezoelectric devices remains a great challenge, largely due to the inherent crystalline nature of piezoelectric materials and electrodes. In this work, for the first time, we report the fabrication of a highly transparent and stretchable piezoelectric device based entirely on polyurethane-urea (PUU) elastomers/composites. Specifically, nano ZnO hybrid hydrophobic PUU serves as the elastic inner piezoelectric layer; conductive ionic liquid composite hydrophilic PUU forms the middle electrode layer; and hydrophobic PUU elastomer acts as the outer encapsulation layer. The obtained device exhibits exceptional stretchability (elongation at break >1000%) and excellent optical transparency (∼86%). It can generate distinct, stable, and reliable output signals for monitoring both small- and large-scale mechanical motions along with a mechanical energy output of 48 μW m^-2 at a pressure of 38.2 kPa, highlighting its outstanding sensing and energy harvesting capabilities. This work presents valuable new insights into the design and development of novel, reliable, transparent, and stretchable piezoelectric devices, paving the way for the new generation of flexible electronics.