High Molar Extinction Coefficient Ion-Coordinating Ruthenium Sensitizer for Efficient and Stable Mesoscopic Dye-Sensitized Solar Cells

Ru(4,4-dicarboxylic acid-2,2'-bipyridine) (4,4'-bis(2-(4-(1,4,7,10-tetraoxyundecyl)phenyl)ethenyl)-2,2'-bipyridine) (NCS)(2), a new high molar extinction coefficient ion-coordinating ruthenium sensitizer was synthesized and characterized using H-1 NMR, Fourier transform IR (FTIR), and UV/vis spectroscopies and cyclic voltammetry. Using this sensitizer in combination with a nonvolatile organic-solvent-based electrolyte, we obtain a photovoltaic efficiency of 8.4% under standard global AM 1.5 sunlight. These devices exhibit excellent stability when subjected to continuous thermal stress at 80 degrees C or light soaking at 60 degrees C for 1000 h. An electrochemical impedance spectroscopy study revealed that device stability is maintained by stabilizing the TiO2/dye/electrolyte and Pt/electrolyte interface during the aging process. The influence of Li+ present in the electrolyte on the device photovoltaic parameters was studied, and the FTIR spectral and photovoltage transient study showed that Li+ coordinates to the triethyleneoxide methylether side chains on the K60 sensitizer molecules.