Polypyridyl Ru(II)-sensitizers with extended π-system enhances the performance of dye sensitized solar cells

New polypyridyl ruthenium(II) complexes “cis-Ru(4,4′-dimesityl-2,2′-bipyridine) (Ln) (NCS)2H102” and “cis-Ru(4,4′-bis(2,3,6-tri-isopropylphenyl)-2,2′-bipyridine) (Ln) (NCS)2H105”, where Ln = 4,4′-dicarboxylic acid-2,2′-bipyridine; were synthesized and successfully applied to sensitization of nano-crystalline TiO2 based solar cells (DSSCs). The DSSCs of H102 and H105 fabricated from 0.16 cm2 TiO2 electrodes exhibited broader comparable photocurrent action spectra with almost identical solar-to-electrical energy conversion efficiency (η) as compared to N719 sensitizer. The incident photon-to-current conversion efficiency (IPCE) values of 98% and 95% were obtained for H102 and H105 sensitizers respectively. Under 1 sun condition, η-values of 8.39% (short-circuit photocurrent (JSC) = 16.4 mA/cm2, open-circuit photo voltage (VOC) = 692 mV, fill factor = 0.734), 8.76% (JSC = 16.3 mA/cm2, VOC = 735 mV, fill factor = 0.734) and 9.12% (JSC = 16.1 mA/cm2, VOC = 745 mV, fill factor = 0.753) were obtained for H102, H105 and N719 sensitizers respectively.