Effects of the aspect ratio of ZnO nanorods on the performance of piezoelectric nanogenerators

This paper presents an investigation on the performance of ZnO nanorod (ZNR)-based piezoelectric nanogenerators (PENGs). ZNRs on the ZnO seed layer coated double-sided flexible polyethylene terephthalate (PET) at different molar concentrations (0.01, 0.05 and 0.1 M) were synthesized by controlling the aspect ratio (length/diameter) of ZNRs, that are closely related to the piezoelectric output potential voltage using a simple hydrothermal method. ZNR PENGs were fabricated with an opposite electrode of gold-coated PET (Au/PET), which was placed on both the top and bottom of the ZNR-coated double-sided PET. X-ray diffraction and field emission scanning electron microscopy images revealed that as the molar concentration increased, the orientation of the as-grown ZNRs became non-uniformly distributed along the c-axis and also along with the decreased aspect ratio. At a low molar concentration (0.01 M), the ZNR PENGs exhibited a relatively high output potential voltage (∼4.48 V) under an external pressing mass (500 g). The ZNR samples grown at 0.05 and 0.1 M exhibited a lower piezoelectric voltage 2.48 and 1.84 V, respectively. These results confirmed that ZNR PENGs with a small diameter, long length (i.e. high aspect ratio) and good alignment tend to be bent more easily for the efficient generation of the piezoelectric potential.