Development and optimisation of a zinc oxide nanowire nanogenerator

[摘要] ENGLISH ABSTRACT: This study developed and optimised zinc oxide (ZnO) nanowire-based nanogenerator.The nanogenerator works on the piezoelectric effect that is, a mechanicalforce is converted to an electrical voltage. The ZnO nanowires are piezoelectricand when any force is applied to the nanowires an output voltage is generated.This ZnO nanowire-based nanogenerator can be used to power small electronicdevices, such as pacemakers. The nanogenerator can also be incorporated intoclothes and shoes to generate electricity to charge a cell phone for example. Theproblem experienced currently is that the nanogenerator does not generate enoughelectricity to be of practical use and needs to be further optimised. Simulations andmathematical models were used to identify areas where the nanogenerator couldbe optimised in order to increase the output voltage. It is shown that the morphologyof the nanowires can have a considerable effect on the output voltage. For thisreason the growth of the nanowires was investigated first. Different methods wereused to propagate the nanowires in order to select the method that, on average,has the highest output voltage. Accordingly, one parameter at a time and design ofexperiments were used to optimise the nanowire growth. Consequently, these twomethods were used to optimise the growth parameters with the respect to the outputvoltage. The aqueous solution method was found to yield nanowires that givethe highest generated output voltage. After growing over 600 nanowire samples,optimal growth parameters for this method were found. These optimal growth parameterswere subsequently used to grow nanowires that were used to manufacturethe nanogenerator. The nanowires were grown on a solid substrate and hencethe nanogenerator was also manufactured on the solid substrate. Through variousoptimisations of the manufacturing process the maximum output voltage achievedwas about 500 mV. However, this output voltage is too low to be of practical use,even though the output has been raised considerably. The main problem was foundto be the fact that the contact between the nanowires and the electrode was weakdue to contamination. A new method was therefore required where the electrodeand the nanowires would be in proper contact to ensure that higher output voltageswere achieved. Subsequently, a flexible nanogenerator was manufactured in order to solve this problem. Accordingly, the nanowires were grown on the flexiblepolyimide film and a buffer layer was then spun onto the flexible substrate, leavingonly the nanowire tips exposed. The electrode was then sputtered on top of thisbuffer layer, covering the nanowire tips. This ensured proper contact between thenanowires and the electrode. The nanogenerator, which was manufactured withnon-optimal growth parameters, gives a maximum voltage output of 1 V, doublethe maximum achieved with the solid nanogenerator. When the optimal growthparameters were used the output voltage was raised to 2 V. Various optimisationtechniques were performed on the nanogenerator, including plasma treatment andannealing and the use of various materials in the buffer layer. Combining theseoptimisation methods subsequently led to an optimised nanogenerator that cangenerate an output voltage of over 5 V. This was achieved after over 1200 nanogeneratorshad been manufactured. However, the output voltage was not in a usableform. Circuitry was therefore developed to transform the voltage generated by thenanogenerator to a useable form. The best circuit, the LTC3588, was used to poweran LED for 10 seconds. The completed device was found to achieve a power outputof 0.3 mW, enough for small electronic devices.

[发布机构] Stellenbosch University