4,5-Diazafluorene ligands and their ruthenium(II) complexes with boronic acid and catechol anchoring groups: design, synthesis and dye-sensitized solar cell applications

Design, synthesis, characterization, and investigation of photovoltaic properties of 4,5-diazafluorene derived diimine ligands (C2, C3) and their ruthenium(II) complexes are reported. FT-IR, H-1 NMR, C-13 NMR, and mass spectroscopic methods were used to elucidate the structures of these compounds. The effect of the number and nature of anchoring groups attached to these ligands and complexes as sensitizers were evaluated for optical properties and photovoltaic performance in dye-sensitized solar cells (DSSCs). The sensitizers bearing catechol show higher power conversion efficiency (PCE) than the dyes with boronic acid due to better binding of the catechol anchoring group on the TiO2 surface. Among these sensitizers, DSSC based on [Ru(C2)(2)(NCS)(2)](PF6)(2) having two catechol anchoring groups gives the best PCE of 2.83%, with J(sc) = 6.40 mA cm(-2), V-oc = 0.632 V and FF = 0.70 in the presence of chenodeoxycholic acid (CDCA) as the coadsorbent, which is attributed to broader spectral response and efficient electron injection. These results suggest that dyes bearing two catechol anchoring groups are promising for efficient DSSCs.