2000 hours photostability testing of dye sensitised solar cells using a cobalt bipyridine electrolyte

DSSCs incorporating Co(II/III) tris(bipyridine) redox couple in acetonitrile and the Z907 dye were subjected to >= 2000 hours of light soaking at 20 degrees C and similar to 1 sun light intensity from white LEDs (similar to no UV component). Initial energy efficiencies were near 6.3%. After 2000 hours, the best acetonitrile based cells maintained similar to 66% of the initial efficiency. Both J(SC) and fill factor (FF) declined, while the V-OC remained highly stable. In comparison, the best Z907/cobalt cells with 3-methoxypropionitrile (MPN) as a solvent, maintained 91% of the initial efficiency after 2000 hour light soaking. Only FF declined in MPN based cells. In follow up testing of similar ACN cells at the maximum power point, at 30 degrees C, the best cells maintained similar to 100% of the initial efficiency after 1000 hours. Impedance, J(SC) vs. intensity and charge extraction data are consistent with a decrease in the Co(III) concentration, or a restriction in Co(III) diffusion, during light soaking.