An alternative efficient redox couple for the dye-sensitized solar cell system

A series of new cobalt complexes [Co(LLL)(2)X-2] were synthesized and evaluated as redox mediators for dye-sensitized nanocrystalline TiO2 Solar cells. The structure of the ligand and the nature of the counterions were found to influence the photovoltaic performance. The one-electron-transfer redox mediator [Co(dbbiP)(2)](ClO4)(2) (dbbip = 2,6- bis(1'-butylbenzimidazol-2'-yl)pyridine) performed best among the compounds investigated. Photovoltaic cells incorporating this redox mediator yielded incident photon-to-current conversion efficiencies (IPCE) of up to 80%. The overall yield of light-to-electric power conversion reached 8 % under simulated AM1.5 sunlight at 100 W m(-2) intensity and more than 4 % at 1000 W m(-2). Photoelectrodes coated with a 2 mum thick nanoporous layer and a 4 mum thick light-scattering layer, sensitized with a hydrophobic ruthenium dye, gave the best results.