A new high molar extinction coefficient ruthenium(II) bipyridyl complex “cis-Ru(4, -bis(9,9-dibutyl-7-(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-fluoren-2-yl)-2, -bipyridine)(2, -bipyridine-4, -dicarboxylic acid)(NCS)2, BPFC” has been synthesized and characterized by FT-IR, -NMR, and ESI-MASS spectroscopes. The sensitizer showed molar extinction coefficient of ？M？1cm？1, larger as compared to the reference N719, which showed ？M？1cm？1. The test cells fabricated using BPFC sensitizer employing high performance volatile electrolyte, (E01) containing 0.05？M I2, 0.1？M LiI, 0.6？M 1,2-dimethyl-3-n-propylimidazolium iodide, 0.5？M 4-tert-butylpyridine in acetonitrile solvent, exhibited solar-to-electric energy conversion efficiency (η) of 4.65% (short-circuit current density ( ) = 11.52？mA/cm2, open-circuit voltage ( ) = 566？mV, fill factor = 0.72) under Air Mass 1.5 sunlight, lower as compared to the reference N719 sensitized solar cell, fabricated under similar conditions, which exhibited η-value of 6.5% ( = 14.3？mA/cm2, = 640？mV, fill factor = 0.71). UV-Vis measurements conducted on TiO2 films showed decreased film absorption ratios for BPFC as compared to those of reference N719. Staining TiO2 electrodes immediately after sonication of dye solutions enhanced film absorption ratios of BPFC relative to those of N719. Time-dependent density functional theory (TD-DFT) calculations show higher oscillation strengths for 4, -bis(9,9-dibutyl-7-(3,6-di-tert-butyl-9H-carbazol-9-yl)-9H-fluoren-2-yl)-2, -bipyridine relative to 2, -bipyridine-4, -dicarboxylic acid and increased spectral response for the corresponding BPFC complex. 1. Introduction Dye sensitized solar cells (DSSCs) attracted intense attention among scientific as well as industrial organizations because of their high photon-to-electricity conversion efficiency and low cost compared to traditional photoelectrochemical cells [1–5]. Since Graetzel introduced the first highly efficient nanocrystalline TiO2 sensitized solar cell based on ruthenium(II) bipyridyl complex, N3 as sensitizer, there have been several modifications to improve the overall performance of the test cell devices [6–22]. Among all the components employed in DSSC, sensitizer plays a key role in photovoltaic performance in respect of efficiency and long-term durability. The important tunable properties of sensitizers for high efficient DSSCs are broad absorption (400 to 900？nm) and high molar extinction coefficient (thin films and solid state DSSCs), thermal and photochemical stability (long durable), compatibility with TiO2 semiconductor
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