Iridium catalyst based counter electrodes for dye-sensitized solar cells

Conventional Pt-based counter electrodes (CEs) in dye-sensitized solar cells (DSSCs) have critical problems such as an expensive cost, dissolution and degradation in the iodine based electrolyte. In order to replace the Pt catalytic layer, as a cheaper and chemically stable material, iridium (Ir)-coated CEs were prepared for the application in DSSCs. The Ir catalytic layers with the thicknesses of 34, 46 and 69 nm were deposited to the fluorine doped tin oxide (FTO) glasses using a thermal evaporator. As the thickness of Ir catalytic layer increases, the sheet resistance decreases, however, the surface crack is enlarged. As a result, the electrocatalytic activity for the I ^-/I3- redox electrolyte was optimized at the thickness of 46 nm, which was confirmed by cyclic voltammograms (CV) and impedance analysis. The photovoltaic performance of DSSC was also greatest when the 46-nm-thick Ir catalytic layer was employed as a CE (the conversion efficiency was 5.19%). Although the conversion efficiency of conventional Pt-coated CE was higher (7.38%), the performance of Ir-coated CE may be further enhanced if the Ir catalytic layer is more conformally coated without crack. These results promise that the Ir can be a suitable material to prepare inexpensive and chemically stable CEs of DSSCs.