Comparative studies of pyridine and bipyridine ruthenium dye complexes with different side groups as sensitizers in sol-gel quasi-solid-state dye sensitized solar cells

Six ruthenium(II) complexes as charge-transfer sensitizers for dye sensitized solar cells (DSSCs) are synthesized. The absorption and electrochemical properties of newly synthesized ruthenium-dye molecules contained one bipyridine (bpy) ligand with two carboxylic groups have been investigated. Among them, four ruthenium(II) complexes contain a second bpy ligand with branching and non-branching side groups containing C and H only and the remaining two ruthenium(II) complexes instead of a second bipyridine (bpy) ligand, they consisted of a pyridine (py) ligand with side groups containing –C–O–C–molecular group. Dye sensitized solar cells employing quasi-solid state electrolyte and the six ruthenium complexes are constructed and electrically characterized under standard conditions of light irradiance (1000 W/m², AM 1.5). Their behavior is compared with that of commercially available ruthenium complex D907 in terms of current-voltage characteristic curves under simulated light and dark while electrochemical impedance spectroscopy showed comparable results for local resistance to charge transfer across the TiO₂-electrolyte interface and free electron lifetimes for two bipyridine and commercial D907 complexes. The influence of molecular side groups into ruthenium-dye molecules is discussed in terms of the cells' efficiency