Impedance Characteristics of Transparent GNP-Pt Ink Catalysts for Flexible Dye Sensitized Solar Cells

Abstract

By thermally reducing platinum onto the surface of Graphene Nanoplatelet (GNP) particles the catalytic activity of the iodide/triiodide reaction in dye-sensitized solar cells (DSC) can be improved significantly. The GNP-Pt particles can be used to formulate a highly catalytic yet transparent ink, which can be deposited by a number of different technologies such as flexographic printing, K-bar, slot-die and spin coating. The catalytic performance of the ink has been characterized using impedance spectroscopy, the impedance spectra show a high frequency impedance curve often seen in carbon electrodes. The origin of this impedance has a number of opposing hypotheses which are critically examined. The data supports the hypothesis that the high frequency curve is due to a contact resistance between the GNP-Pt ink and the FTO. In addition to the high frequency curve, a previously unresolved low frequency impedance is identified. When fabricated into DSCs the ink catalyst demonstrates cell efficiencies up to 5.2% and is shown to have a similar performance to conventional sputtered platinum when used in a reverse illuminated DSC (through the counter electrode). The first flexible reverse illuminated DSC with a GNP-Pt ink catalyst, suitable for roll-to-roll deposition is reported with an efficiency of 2.6%.