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

Abstract

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 °C and ∼1 sun light intensity from white LEDs (∼no UV component). Initial energy efficiencies were near 6.3%. After 2000 hours, the best acetonitrile based cells maintained ∼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 °C, the best cells maintained ∼100% of the initial efficiency after 1000 hours. Impedance, J_SCvs. 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.