A mixture of Co(phen)(3+/2+) and Co(EtPy)(3+/2+) complexes, where EtPy is a terpyridine ligand bearing an 3,4- ethylenedioxythiophene (EDOT) substituent, has been used as redox mediator in dye-sensitized solar cells. This combination of cobalt complexes allows an electron cascade leading to enhanced cell efficiency. To explain this result, we propose a synergy between the EDOT-functionalized cobalt complex and the PEDOT counter-electrode, which favors electron transfer and reduces recombination. (C) 2015 Elsevier Ltd. All rights reserved.