Synthesis and photovoltaic properties of novel ruthenium(II) sensitizers for dye-sensitized solar cell applications

Three heteroleptic ruthenium sensitizers, Ru(L)(L¹)(NCS)₂ [L = 4,4′-dicarboxylic acid-2,2′-bipyridine, Ru-T1: L¹ = (E)-2-(4′-methyl-2,2′-bipyridin-4-yl)-3-(thiophen-2-yl)acrylonitrile, Ru-T2: L² = (E)-3-(5′-hexyl-2,2′-bithiophen-5-yl)-2-(4′-methyl-2,2′-bipyridin-4-yl)acrylonitrile, and Ru-T3: L³ = (E)-3-(5″-hexyl-2,2′:5′,2″-terthiophen-5-yl)-2-(4′-methyl-2,2′-bipyridin-4-yl)acrylonitrile)], were synthesized and used as photosensitizers in nanocrystalline dyesensitized solar cells (DSSCs). The introduction of the 3-(5-hexyloligothiophen-5-yl)acrylonitrile group increased the conjugation length of the bipyridine donor ligand and thus improved their molar absorption coefficient and light harvesting efficiency. DSSCs with the configuration of SnO₂: F/TiO₂/ruthenium dye/liquid electrolyte/Pt devices were fabricated using these Ru-T1~T3 as a photosensitizers. Among the devices, the DSSCs composed of Ru-T2 exhibited highest power conversion efficiency (PCE) of 2.84% under AM 1.5 G illumination (100 mW/cm²).