6533b7defe1ef96bd1275b1a

RESEARCH PRODUCT

A Bis(tridentate)cobalt Polypyridine Complex as Mediator in Dye‐Sensitized Solar Cells

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description

Dye-sensitized solar cells equipped with cationic and neutral RuII-based sensitizers [Ru(ddpd){tpy(COOH)3}]2+ [12+; ddpd = N,N′-dimethyl-N,N′-di(pyridin-2-yl)pyridin-2,6-diamine, tpy(COOH)3 = 2,2″6′,2″-terpyridine-4,4′,4″-tricarboxylic acid] and [Ru(ddpd){tpy(COOH)(COO)2}] (2) with and without the coadsorbent chenodeoxycholic acid were constructed with I3–/I– or the CoIII/II-based redox mediators [Co(bpy)3]3+/2+ (33+/2+; bpy = 2,2′-bipyridine) and [Co(ddpd)2]3+/2+ (43+/2+) in the presence of LiClO4 and 4-tert-butylpyridine. The best photovoltaic performance was achieved by using the 43+/2+ shuttle and the neutral sensitizer 2 without coadsorbent. The higher short-circuit photocurrent density and higher electron recombination lifetimes obtained with this combination suggest slow electron recombination kinetics at the TiO2 surface with the CoIII complex 43+. The slow electron transfer to 43+ is tentatively ascribed to the high-lying π* orbitals of the electron-rich ddpd ligands, which result in a weak electronic coupling. This contrasts with the faster recombination with 33+, which features the low-energy π* orbitals of the bpy ligands.