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 α-phase of PVDF to its β-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 μA. A maximum power density of 50.6 μW cm⁻² was obtained at a loading resistance of 0.4 MΩ, 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.