High-Voltage Dye-Sensitized Solar Cells Mediated by [Co(2,2'-bipyrimidine)₃]^z

The cobalt complex [Co(2,2'-bipyrimidine)₃](PF₆)₂ (Co-bpm) was tested as a redox mediator in the dye-sensitized solar cell. The measured photovoltages for the cells were in excess of 1 V, which is approximately 3-fold greater than that measured for devices where [Co(2,2'-bipyridine)₃](PF₆)₂ (Co-bpy) was used as the redox mediator under the same experimental conditions. The root cause of this voltage enhancement is the Co^III/Co^II redox potential for Co-bpm being positively shifted by 0.50 V relative to the Co-bpy mediator. This result highlights how the number and position of the N atoms in aromatic ligands can have a profound effect on the measured photovoltage.