A channel flow cell system specifically designed to test the efficiency ofredox shuttles in dye sensitized solar cells

The construction and use of a thin layer flow cell test system employing a TiO2 working electrode, a platinum quasi-reference electrode and the ruthen ium dye (H-2-dcbpy)Ru(NCS)(2) (H-2-dcbpy = 2,2'-bipyridine-4,4'-dicarboxyli c acid) is described. The efficient design enables significant advantages t o be gained over presently available procedures for the measurement of phot ocurrents of dye-sensitized solar cells. The widely used iodide/triiodide r edox shuttle system has been investigated over a wide range of conditions. A linear dependence of photocurrent on cation radius was revealed. Under ce rtain conditions, the photocurrent measured in the presence of the Li+ cati on is five times larger than when the (C4H9)(4)N+ cation is used. Additiona lly, the addition of low concentrations of cations with small diameters has a significant catalytic enhancement effect on the photocurrent. Other redo x shuttles, based on ferrocene, thiocyanate, triiodide and bromide, were te sted for their performance in the flow cell and compared to iodide. However , despite some apparent thermodynamic advantages, the photocurrents obtaine d with these redox shuttles were more than two orders of magnitude lower th an those measured with iodide. This finding implies that the efficiency of redox shuttles is limited by kinetic restraints rather than their thermodyn amic properties and confirms that the iodide/triiodide system is the domina nt redox shuttle. (C) 2001 Elsevier Science B.V. All rights reserved.