New ruthenium sensitizers containing styryl and antenna fragments

Amphiphilic ligands 4′-((4-(5-pyridin-4-yloxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L1), 4,4′-bis((E)-4-(5-(pyridin-4-yloxy)pentyloxy)styryl)-2,2′-bipyridine (L2), 4′-(4-(5-(4′-cyano-4-biphenoxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L3), and 4′-(4-(5-(zinc tetrakis-5,10,15-tritolyl-20-(4-hydroxyphenyl)porphyrin)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L4) and their heteroleptic ruthenium(II) complexes of the types [Ru(L1)(L)(NCS)2] (D20), [Ru(L2)(L)(NCS)2] (D21), [Ru(L3)(L)(NCS)2] (D22), and [Ru(L4)(L)(NCS)2] (D23) (where L = 4,4′-bis(carboxylic acid)-2,2′-bipyridine) have been synthesized, as photosensitizers for nanocrystalline dye-sensitized solar cells. All complexes D20–D23 exhibit a broad MLCT band around 520–530 nm in DMF and an emission band around 740–790 nm in DMF. We have studied photovoltaic performances based on the newly synthesized dyes. Under standard AM 1.5 sunlight, the dye D20 gave a short-circuit photocurrent density of 13.31 mA/cm2, an open-circuit voltage of 0.64 V, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 5.81%.