Tuning the spectroscopic, electrochemical, and photovoltaic properties of triaryl amine based sensitizers through ring-fused thiophene bridges.

The ring-fused thiophene derivatives benzo[c]thiophene and its precursor bicyclo[2.2.2]octadiene (BCOD) have been introduced as π-conjugated spacers for organic push-pull sensitizers with dihexyloxy-substituted triphenylamine as donor and cyanoacrylic acid as acceptor (OL1-OL6). The effects of the fused ring on the spectroscopic and electrochemical properties of these sensitizers and their photovoltaic performance in dye-sensitized solar cells have been evaluated. Introduction of a binary benzo[c]thiophene and ethylenedioxy thiophene as π bridge caused a significant red shift of the characteristic intramolecular charge-transfer band to 642 nm. It is found that the sensitizer OL3, which contains one benzo[c]thiophene unit as π linker, gives the highest overall conversion efficiency of 5.03% among all these dyes.