A tandem redox system with a cobalt complex and 2-azaadamantane-N-oxyl for fast dye regeneration and open circuit voltages exceeding 1 V

A new tandem electrolyte composed of two redox pairs, the organic radical 2-azaadamantane-N-oxyl (AZ) and the well-known redox pair [Co(bpy)(3)](3+/2+) was investigated in dye sensitized solar cells. Importantly, an increase in V-OC was achieved using the new tandem redox system with values up to 1007 mV, compared to only 896 mV for the reference [Co(bpy)(3)](3+/2+) couple. Consequently, the tandem electrolytes presented higher device performance in conjunction with the organic dye XY1. It was determined that the V-OC improvement is mainly attributed to the combined effect of two factors: the more positive redox potential of the small donor AZ (0.81 V vs. SHE) and improved recombination resistance in the tandem electrolytes