A ThiopheneBased Anchoring Ligand and Its Heteroleptic Ru(II)Complex for Efficient ThinFilm DyeSensitized Solar Cells

A novel heteroleptic Ru II complex (BTC-2) employing 5,5 ′ -(2,2 ′ -bipyridine4,4 ′ -diyl)bis (thiophene-2-carboxylic acid) (BTC) as the anchoring group and 4,4 ′ dinonyl-2,2 ′ -bipiridyl and two thiocyanates as ligands is prepared. The photovoltaic performance and device stability achieved with this sensitizer are compared to those of the Z-907 dye, which lacks the thiophene moieties. For thin mesoporous TiO 2 fi lms, the devices with BTC-2 achieve higher power conversion effi ciencies than those of Z-907 but with a double-layer thicker fi lm the device performance is similar. Using a volatile electrolyte and a double layer 7 + 5 μ m mesoporous TiO 2 fi lm, BTC-2 achieves a solarto-electricity conversion effi ciency of 9.1% under standard global AM 1.5 sunlight. Using this sensitizer in combination with a low volatile electrolyte, a photovoltaic effi ciency of 8.3% is obtained under standard global AM 1.5 sunlight. These devices show excellent stability when subjected to light soaking at 60 ° C for 1000 h. Electrochemical impedance spectroscopy and transient photovoltage decay measurements are performed to help understand the changes in the photovoltaic parameters during the aging process. In solid state dye-sensitized solar cells (DSSCs) using an organic hole-transporting material (spiro-MeOTAD, 2,2 ′ ,7,7 ′ -tetrakis-( N , N -di-p-methoxyphenylamine)9,9 ′ -spirobifl uorene), the BTC-2 sensitizer exhibits an overall power conversion effi ciency of 3.6% under AM 1.5 solar (100 mW cm − 2 ) irradiation.