Synthesis and Characterization of Novel Heteroleptic Ru(II) Bipyridine Complexes for Dye-Sensitized Solar Cell Applications

Four heteroleptic ruthenium(II) complexes, [Ru(L1)(L2)(NCS)2] (where L1 = 4,4′-bis[2-(1,1′-biphenyl)-4-ylethenyl]-2,2′-bipyridine (bpbpy) or 4,4′-bis[2-(3,4-dimethoxyphenyl)ethenyl]-2,2′-bipyridine (dmpbpy); L2 = 4,4′-dicarboxy-2,2′-bipyridine (dcbpy) or 4,4′-bis(E-carboxyvinyl)-2,2′-bipyridine (dcvbpy)), were synthesized from a one-pot reaction of [RuCl2(p-cymene)]2 and L1 followed by the addition of the anchoring ligand, L2. From these new heteroleptic ruthenium(II) complexes containing carboxylic acid-functionalized ligands, the tetrabutylammonium salt forms of the ruthenium(II) complexes, [Ru(L1)(L2)(NCS)2][TBA], were obtained in reasonable yields and applied as dyes in dye-sensitized solar cell (DSSC) devices. Among the DSSCs fabricated with the [Ru(L1)(L2)(NCS)2][TBA] dyes, a DSSC fabricated with the [Ru(bpbpy)(dcbpy)(NCS)2][TBA] dye exhibited the best power conversion efficiency (η) of 4.27%, while the cells fabricated with other dyes had η between 1.94 and 2.68%.