Characterization and Application of Ru2+ Complex with Square-Planar Quadridentate Ligand Containing Arylamines for Dye-Sensitized Solar Cells

A square-planar quadridentate ligand with two N -arylamine groups, dimethyl-6,6$'$-bis(methyl-2-pyridylamino)-2,2$'$-bipyridine-4,4$'$-dicarboxylate ( L ), and its Ru 2+ complex [Ru L (trans-NCS) 2 ] ( K1 ) were newly synthesized as a sensitizer for dye-sensitized solar cells (DSSCs). The ligand L enforces the trans coordination of two thiocyanate ligands to the Ru 2+ center of K1 , resulting in the extension of its absorption bands to the near-infrared region (${\sim}900$ nm). The energy conversion efficiency ($\eta$) of the DSSC based on K1 was 5.2%. This low $\eta$ value in comparison with those of other dyes ( N3 and N719 ) is explained by its self-aggregation and its low molar absorbance coefficient in the visible light region. The incident photo-to-current conversion efficiency (IPCE) spectrum of the DSSC based on K1 clearly indicated that this dye was able to utilize near-infrared-region light efficiently as compared with that of N719 dye.