Ruthenium(II) photosensitizers with electron-rich diarylamino-functionalized 2,2′-bipyridines and their application in dye-sensitized solar cells

New ruthenium(II) photosensitizers [Ru(dcbpy)(L)(NCS)₂] (dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine; L = 4,4′-bis{di[4-(N,N′-dimethylamino)phenyl]amino}-2,2′-bipyridine (1), 4,4′-bis[di(4-methoxyphenyl)amino]-2,2′-bipyridine (2), and 4,4′-bis[di(4-tolyl)amino]-2,2′-bipyridine (3)) were prepared and characterized and their application in dye-sensitized solar cells is presented. The optical absorption of these photosensitizers gives a peak at around 540 nm, which is very similar to that of the standard N719. The maximum incident photon-to-current conversion efficiency (IPCE) of 80.6% was obtained for 3, which corresponded to a power conversion efficiency (η) of 5.68% under standard air mass (AM) 1.5 sunlight (versus N719 at 6.76%). Molecular cosensitization of 3 with an organic dye, QS-DPP-I, yielded higher η values up to 6% relative to the cells based on individual photosensitizers, and the corresponding IPCE can reach 93.6% at 549 nm. A preliminary stability test of the devices was also conducted.