# Photo-supercapacitors based on nanoscaled ZnO

## TL;DR

This paper explores how different ZnO nanostructures affect the performance of photo-supercapacitors, showing that nanowires outperform nanoflowers under UV light.

## Contribution

The study introduces a new design for photo-supercapacitors using ZnO nanowires, demonstrating enhanced performance under UV light due to fewer structural defects.

## Key findings

- ZnO nanowires (NW) showed a 3-fold increase in Coulombic efficiency under UV light compared to nanoflowers (NF).
- NW-based P-SCs achieved an energy density of 78.1 mWh kg−1 and retained 100% capacitance after 3000 cycles.
- High core defects in NF powders reduced their performance compared to NW structures.

## Abstract

In this study, zinc oxide (ZnO) powders in two different morphologies, nanowire (NW) and nanoflower (NF), have been synthesized by the hydrothermal method. The eligibility of the pristine ZnO nanopowders as a photo-active material has been revealed by designing P-SC devices via the facile drop-casting method on both glass and plastic substrates in large-area applications. The impact of physical properties and especially defect structures on photo-supercapacitor (P-SC) performance have been explored. Although the dark Coulombic efficiency (CE%) of both NW and NF-based P-SC were very close to each other, the CE% of NW P-SC increased 3 times, while the CE% of NF P-SC increased 1.7 times under the UV-light. This is because the charge carriers produced under light excitation, extend the discharge time, and as confirmed by electron paramagnetic resonance, photoluminescence, and transmission electron microscopy analyses, the performance of P-SCs made from NF powders was relatively low compared to those produced from NW due to the high core defects in NF powders. The energy density of 78.1 mWh kg−1 obtained for NF-based P-SCs is very promising, and the capacitance retention value of almost 100% for 3000 cycles showed that the P-SCs produced from these materials were entirely stable. Compared to the literature, the P-SCs we propose in this study are essential for new generation energy storage systems, thanks to their ease of design, adaptability to mass production for large-area applications, and their ability to store more energy under illumination.