Optically Transparent Cathode for Dye-Sensitized Solar Cells Based on Graphene Nanoplatelets

摘要

Commercial graphene nanoplatelets in the form of optically transparent thin films on F-doped SnO_2 (FTO) exhibited high electrocatalytic activity toward I_3?/I? redox couple, particularly in electrolyte based on ionic liquid (Z952). The charge-transfer resistance, R_(CT), was smaller by a factor of 5?6 in ionic liquid, compared to values in traditional electrolyte based on methoxypropionitrile solution (Z946). Optical spectra and electrochemical impedance confirm that the film’s absorbance scales linearly with R_(CT)~(?1). Electrocatalytic properties of graphene nanoplatelets for the I_3?/I? redox reaction are proportional to the concentration of active sites (edge defects and oxidic groups), independent of the electrolyte medium. Dye-sensitized solar cell (DSC) was assembled with this material as a cathode. Semitransparent (>85%) film of graphene nanoplatelets presented no barrier to drain photocurrents at 1 Sun illumination and potentials between 0 and ca. 0.3 V, but an order of magnitude decrease of R_(CT) is still needed to improve the behavior of DSC near the open circuit potential and, consequently, the fill factor. We predict that the graphene composite is a strong candidate for replacing both Pt and FTO in cathodes for DSC.