Heteroleptic Ruthenium Sensitizers That Contain an Ancillary Bipyridine Ligand Tethered with Hydrocarbon Chains for Efficient Dye-Sensitized Solar Cells

Abstract

New heteroleptic ruthenium complexes have been synthesized and used as the sensitizers for dye-sensitized solar cells (DSSCs). The ancillary bipyridine ligand contains rigid aromatic segments (fluorene-, carbazole-, or dithieno[3,2-b:2',3'-d]pyrrole-substituted bipyridine) tethered with a hydrophobic hexyl substituent. The conjugated aromatic segment results in significant bathochromic shift and hyperchromic effects in these complexes compared with Z907 (cis-[RuLL'(NCS)(2)]; L=4,4'-dicarboxylic acid-2,2'-bipyridine, L'=4,4'-dinonyl-2,2'- bipyridine). The long hydrocarbon chains help to suppress the dark current if appropriately disposed. DSSCs that use these complexes exhibit very impressive conversion efficiencies (5.94 to 6.91 %) that surpass that of Z907-based (6.36 %) DSSCs and are comparable with that of N719-based standard cells (7.13 %; N719=cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II) bis(tetrabutylammonium)) fabricated and measured under similar conditions (active area: 0.5×0.5 cm(2); AM 1.5 sunlight).