GO/ZnO-based all-solid-state photo-supercapacitors: Effect of GO:ZnO ratio on composite properties and device performance

Abstract

The development of photo-supercapacitors (PSC), which is an important step towards more efficient use of solar energy and reducing the carbon footprint, will be possible with a better understanding and manipulation of the properties of photo-active dual-effect electrodes used in these devices. This work demonstrates the existence of critical ratios for graphene oxide/zinc oxide (GO/ZnO) composites in terms of PSC performance. In this ratio, both photoluminescence intensity in the UV region and the defect densities determined from electron paramagnetic resonance spectroscopy are low. Moreover, the specific capacitance of the best-performing GO/ZnO composites increased 2.7-fold and reached 6612 mFg(-1) after UV illumination. Besides, this device showed exceptional stability over 30,000 galvanostatic charge and discharge cycles with 99.6 % capacitance retention and 100 % Coulombic efficiency. The maximum energy density of 6.3 Whkg(-1) and power density of 625 Wkg(-1) were calculated for a 2.5 V operating voltage under UV illumination. As proof of concept, a digital watch was powered for more than 1 h and 40 min with GO/ZnO-based PSC charging under UV and AM1.5 sunlight illumination at 0.2 Ag-1 for 50 and 130 s, respectively.