Enhanced-Light-Harvesting Amphiphilic Ruthenium Dye for Efficient Solid-State Dye-Sensitized Solar Cells

A ruthenium sensitizer (coded C101, NaRu (4,4'-bis(5-hexylthiophen-2-yl)-2,2'-bipyridine) (4-carboxylic acid-4'-caboxylate-2,2'-bipyridine) (NCS)(2)) containing a hexylthiophene-conjugated bipyridyl group as an ancillary ligand is presented for use in solid-state dye-sensitized solar cells (SSDSCs). The high molar. extinction coefficient of this dye is advantageous compared to the widely used Z907 dye, (NaRu (4-carboxylic acid-4'-carboxylate) (4,4'-dinonyl-2,2'-bipyridine) (NCS)(2)). In combination with an organic hole-transporting material (spiro-MeOTAD, 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine) 9, 9'-spirobifluorene), the C101 sensitizer exhibits an excellent power-conversion efficiency of 4.5% under AM 1.5 solar (100 mW cm(-2)) irradiation in a SSDSC. From electronic-absorption, transient-photovoltage-decay, and impedance measurements it is inferred that extending the pi-conjugation of spectator ligands induces an enhanced light harvesting and retards the charge recombination, thus favoring the photovoltaic performance of a SSDSC.