Controlling the nanoscale morphology and structure of the ZnO/MnO2 system for efficient transparent supercapacitors

We discuss relationships between transparent supercapacitor performance and the morphology of its ZnO nanostructured electrodes. The electrodes with different morphologies were prepared by magnetron sputtering and postdeposition annealing. They were decorated with MnO2 nanostructures and tested in symmetric transparent supercapacitors. The capacitances for discharging at 10 µA/cm2 were in the range of 20–53 µF/cm2, meaning that an increase of 250% in capacitance can be obtained by optimizing the electrode morphology. Optimal morphologies were hierarchical with a large range of pore sizes available. The worst performing had the smallest range of pore sizes. Best devices exhibited transparencies above 90%.