Synergistic contribution of flexoelectricity and piezoelectricity towards a stretchable robust nanogenerator for wearable electronics

The fabrication of a high-performance piezoelectric nanogenerator (PENG) with high stretchability and durability is desirable for the next-generation of stretchable and wearable electronics. Herein, an eco-friendly and stretchable flexoelectricity-enhanced piezoelectric nanogenerator (F-PENG) based on zinc-aluminum layered double hydroxide nanosheets (ZnAl:LDH Ns)-ZnO heterostructure is demonstrated on stretchable polydimethylsiloxane (PDMS) substrates. The vertically-oriented eco-friendly ZnAl:LDH Ns are facilely synthesized by dipping the 10 wt% aluminum-doped zinc oxide (AZO) thin films in deionized (DI) water at room temperature. The enhanced output performance of the F-PENG is demonstrated under tapping, bending, and stretching modes, and is attributed to the synergistic flexoelectric and piezoelectric effects. The achieved maximum output power density of F-PENG under tapping is ~2.7 µW/cm2. The pressure-sensing capability of the F-PENG is demonstrated by the generated outputs under the three applied modes. In addition, the biomechanical energy harvesting capability of the F-PENG is demonstrated by subjecting it to various biomechanical motions. The F-PENG exhibits an excellent mechanical durability in all three modes of operation. The present study not only paves the way towards the facile fabrication of stretchable and high-performance F-PENGs with combined flexoelectric and piezoelectric effects, but also validates a wide range of applications in the next generation of stretchable and wearable electronics.