Integrated photocapacitors based on dye-sensitized TiO2/FTO as photoanode and MnO2 coated micro-array CNTs as supercapacitor counter electrode with TEABF4 electrolyte

Abstract

Harvesting solar energy using dye-sensitized solar cells (DSSCs) has been a promising option. Successful integration of a DSSC electrode with an energy storage electrode represents the next challenge for the researchers. In this paper, the fabrication and characterization of an integrated dye-sensitized photoanode and a supercapacitor cathode or a photocapacitor has been presented. This novel device employs N-719 dye-sensitized titanium dioxide on fluorine-doped tin oxide glass substrate as the photoanode. The supercapacitive counter electrode comprises MnO2 coated, vertically aligned, micro-array patterned carbon nanotubes (MA-CNTs). The CNTs were grown on n++ silicon (Si) substrates in a hot filament chemical vapor deposition system followed by in-situ electrochemical deposition of MnO2. Tetraethyl ammonium tetrafluoroborate electrolyte was used to investigate the photovoltaic and energy storage performances of the photocapacitors under 1-sun illumination and constant-current discharge tests. A high discharge capacitance of 13 mF/cm2 at 0.932 V was achieved by coating MnO2 onto the high surface area of MA-CNTs due to the pseudocapacitive behavior of MnO2, which led to a nearly 3-fold increase in the short circuit current density to 0.749 mA/cm2 and more than a 2-fold enhancement in the open circuit voltage to 0.46 V, as compared to the baseline CNT counter electrode. The corresponding increase in the fill factor and efficiency was also observed. Overall, we have demonstrated the viability of a compact, easy to fabricate, integrated photocapacitor with promising energy generation/storage performance.