Beta-phase transformation of polyvinylidene fluoride with supersonically sprayed ZnSnO₃ cuboids for flexible piezoelectric nanogenerators

Flexible self-powered electromechanical devices, such as piezoelectric nanogenerators (PENGs), which are used in wearable and implantable devices, are emerging as state-of-the-art clean energy sources. In this study, a scalable supersonic spraying technique was used to prepare flexible piezocomposite films of polyvinylidene fluoride (PVDF) and hydrothermally synthesized ZnSnO3 (ZSO) cubes for PENGs. Raman spectra confirmed that the transformation of the alpha-phase of PVDF to its beta-phase was induced by the shear stress generated between the ZSO particles and PVDF polymer during supersonic spraying. The optimized sample comprising 0.43 g of ZSO cubes and 1 g of PVDF produced a maximum piezopotential of 41.5 V and a short-circuit current, I-sc, of 52.5 mu A. A maximum power density of 50.6 mu W cm(-2) was obtained at a loading resistance of 0.4 M Omega, which matched the impedance of the PENG. Long-term tapping and bending cycles of N-tap = 4200 and N-bend = 600 yielded piezopotentials of 40.5 and 1.7 V, respectively. In addition, electrical poling for 2 h increased the piezopotential to 52 V owing to the alignment of the ferroelectric dipoles in the PVDF.