Bifunctional WO₃ Photoelectrodes Decorated by Inkjet Printing for Solar Supercapacitors

Abstract 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 WO 3 as a bifunctional material for solar rechargeable supercapacitors, paving the way for the development of new fully integrated devices for the energy sector.