Flexible Oxide-Polymeric Composites for Piezoelectric Energy Harvesting

In this study is presented technology for fabrication of a piezoelectric element as an alternative energy source (energy harvesting). The elements are produced on flexible polyethylene naphthalate (PEN) substrates and consist of novel lead-free nanocomposite [Ga-doped ZnO (GZO) - polyvinylidene fluoride (PVDF)]. The oxide film is deposited by vacuum radiofrequency (RF) sputtering and PVDF is pulverized by spray coating system. Aluminum and gold metal coatings are investigated as electrodes for optimal extraction of the generated electric energy from the piezoelectric coating. It was showed that PVDF spray deposition reduces the surface roughness of GZO film with 1.4 %. Piezoelectric response is measured at different applied dynamic loads with the two types of electrodes, as well as for oxide-only film. It was found that PVDF based composite leads to improved interface conditions for electrode coating, such as low parasitic capacitances. The highest obtained piezoelectric voltage is ~ 586 mV at 40 g mass weight load with frequency of 50 Hz for gold coated GZO+PVDF. This voltage is 41% higher and more stable in the time sweep in comparison with the case at PVDF-free piezoelectric film, and 29% higher than the composite element, but with aluminum electrode. The interface capacitance is 3 orders of magnitude lower (nF vs µF) and the contact resistance is 15 times smaller (Ω vs kΩ) when the interfaces are with gold, which optimizes the electric energy collection and enhances the energy harvesting performance.