Bifunctional WO3 Photoelectrodes Decorated by Inkjet Printing for Solar Supercapacitors

Tungsten oxide-based photoelectrodes for solar supercapacitor applications are initially prepared by screen printing. After a complete functional characterization, the obtained results show the ability of these films to increase the number of stored charges when illuminated due to a diffusion mechanism and finally to produce an areal capacitance of 1.6 and 0.7 mF cm−2 under illumination or in the dark, respectively. Decorating the as-produced electrodes by inkjet printing allowed us to increase their exposed surface area, thus enhancing the areal capacitance up to 2.2 mF cm−2 while reducing charge-transfer resistances. Finally, gel-state symmetrical devices with agar-agar-based electrolyte are prepared and tested with different illumination intensities. At high illumination (1000 W m−2), an areal capacitance of 2.5 mF cm−2 is recorded, however, at low illumination conditions (500 W m−2), the highest value of 7.9 mF cm−2 is obtained (at 0.3 mA cm−2) due to reduced recombination phenomena between the photogenerated charges and the applied current density. This work demonstrates the potentiality of WO3 as a bifunctional material for solar rechargeable supercapacitors, paving the way for the development of new fully integrated devices for the energy sector.