Synthesis and Study of the Physical and Photovoltaic Properties of Novel Heteroleptic Ruthenium(II) Complexes Ligated with Highly π-Conjugated Bipyridine Ancillary and Phenanthroline Anchoring Ligand for Dye-Sensitized Solar Cells

Six new heteroleptic ruthenium(II) complexes (JM1–JM6), each bearing a highly π-conjugated bipyridine ancillary ligand (a methoxy-substituted analog (L1) and a phenanthroline-type anchoring ligand (L2) (dcphen or dcvphen; [Ru(L)2(NCS)2][TBA]2; L1 = 4,4′-bis{2-(3,4-dimethoxyphenyl)ethenyl}-2,2′-bipyridine (dmpbpy), 4,4′-bis{2-(1,1′-biphenyl)-4-ylethenyl}-2,2′-bipyridine (bpbpy), or 4,4′-bis{2-(4′-methoxy-[1,1′-biphenyl]-4-ylethenyl}-2,2′-bipyridine (mbpbpy); L2 = 4,7-dicarboxy-1,10-phenanthroline (dcphen) or 4,7-bis(E-carboxyvinyl)-1,10-phenanthroline (dcvphen)) were synthesized, and their physical and photovoltaic properties were investigated. Various dye-sensitized solar cells (DSSCs) were fabricated using heteroleptic ruthenium(II) complexes. Ruthenium(II) complex JM1, ligated to dmpbpy (ancillary) and dcphen (anchoring) ligands, exhibited the maximum power conversion efficiency (PCE) value of 3.40%, which was approximately 71% of the efficiency exhibited by the commercially available N719-sensitized solar cells. Ruthenium(II) complex JM5, ligated to mbpbpy (ancillary) and dcphen (anchoring) ligands, exhibited the second-best PCE value (2.52%), and ruthenium(II) complex JM3, ligated to bpbpy (ancillary) and dcphen (anchoring) ligands, exhibited a PCE value of 1.45%. It was observed that the PCE values of the DSSCs could be significantly improved by introducing the electron-donating methoxy group at proper positions of the ancillary ligands present in the heteroleptic ruthenium(II) complexes (such as JM1 and JM5).