Polymeric seed layer as a simple approach for nanostructuring of Ga-doped ZnO films for flexible piezoelectric energy harvesting

RF sputtering is used for the growth of Ga-doped ZnO (GZO) piezoelectric film (420 nm) on conjugated polymer PEDOT:PSS deposited on a flexible substrate. The PEDOT:PSS serves as an amorphous seed sublayer for nanostructured GZO growth and as a bottom electrode in a simple energy harvesting element. Dendrite type structure of the piezoelectric film is obtained and it is organized in a single-directional nanoporous manner, which increased the specific surface area of the material and facilitates piezoelectric voltage generation. As a result, the open-circuit voltage reached maximum 398 mV for the nanostructured GZO film on polymer electrode versus 231 mV for the film grown on the metal electrode at low frequency (up to 50 Hz) and weak mechanical loading (max. 40 g). X-ray diffraction spectrum of the GZO nanostructured film is similar to that of ZnO wurtzite structure. FTIR study shows that the Ga doping doesn't affect the wurtzite structure of the host material and does not cause modification of the chemical bond types. The output electrical power was calculated to be 2.05 mu W and 3.34 mu W, corresponding to non-structured and structured GZO films, respectively. This result is competitive with the recent reports for lead-free piezoelectric energy harvesting using conventional microfabrication technologies.