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 (eta) 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 eta 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.