High quality, controlled-structure nanowires (NWs), grown on a transparent flexible substrate, have attracted great
interest as a mean of harvesting solar and mechanical energy. Clarifying their optical and piezoelectric properties is
essential for this application. In this paper, vertically aligned lithium (Li) doped p-type ZnO NWs were grown, on a
micro-patterned transparent flexible polyethylene naphthalate (PEN) substrate, by electrochemical deposition at 88 °C.
The substrate was coated with aluminum-doped ZnO (AZO) thin layer, which served as a good seed layer and a
transparent conductive oxide layer. Varying the seed layer thickness gave control of the individual NWs’ diameter,
density and alignment. The effect of doping on the optical band-gap, crystalline quality and Schottky barrier were
investigated by X-ray diffraction (XRD) spectroscopy and piezoelectric characterization. The piezoelectric polarization
induced piezo-potential in strained ZnO NWs can drive the flow of electrons without an applied electric bias, thus can be
used to harvest mechanical energy and convert it into electricity. To prove this concept, flexible piezoelectric energy
harvesters based on an array of ZnO NWs were fabricated. Results show that the patterned p-type NW-based energy
harvester produces 26-fold output voltage and 19-fold current compared to the conventional un-doped ZnO NW energy
harvester from the same acceleration input.