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A new high molar extinction coefficient ruthenium(II) bipyridyl complex 'cis-Ru(L1)(2,2 -bipyridine-4,4 -dicarboxylic acid) (NCS) 2 , BDF', where L1 = 4,4-bis(9,9-dibutyl-9H-fluorene-2-yl)-[2,2] bipyridine, has been synthesized and characterized by Fourier transform infrared (FTIR), hydrogen nuclear magnetic resonance ( 1 H-NMR) and electrospray ionization mass (ESI-MASS) spectroscopes. The dye, upon anchoring onto mesoporous nano-crystalline TiO 2 solar cells, exhibited a broader photocurrent action spectrum, with a solar-to-electric energy conversion efficiency (η) of 6.58% (J SC = 14.66 mA cm −2 , V OC = 640 mV, fill factor = 0.71) under sunlight at air mass (AM) 1.5, larger than the reference Z907 sensitized solar cell fabricated under similar conditions, which exhibited an η-value of 4.65% (J SC = 11.52 mA cm −2 , V OC = 566 mV, fill factor = 0.72). Absorption measurements and time-dependent density functional theory (TDDFT) calculations show that the increased conjugation length by introducing 9,9-dibutyl-9H-fluorene moiety relatively enhances the spectral response of the ancillary ligand and the corresponding BDF complex. The calculated dipole moments for BDF and Z907 are 17.71 and 16.34 Debye, respectively. The first three highest occupied molecular orbitals (HOMOs) of BDF have a t 2g character, as observed in Z907, while HOMO-4 and HOMO-5 have considerable sizable mixing from Ru-NCS with π-orbitals of L1.

The photovoltaic performance of the heterolepticH102 andHRD2 sensitizers was measured in DSSC and compared with that of reference N719 under similar fabrication and evaluation conditions. The Dye-Sensitised TiO2electrodes were prepared by staining the electrodes in ethanol bath and 1/1 v/v acetonitrile/tert-butanol (binary liquid) mixture bath separately and the DSSCs based on these sensitizers show that the change of dye bath from ethanol to the binary liquid mixture enhances the photocurrent action spectrum and solar-to-electricity conversion efficiencies, (η). Using ethanol for sensitisation of TiO2electrodes, the efficiencies obtained forH102,HRD2 and N719 are 4.31%, 4.62%, and 5.46%, respectively, while in binary liquid mixture bath, the corresponding values are enhanced to 5.89%, 4.87%, and 7.23%, respectively, under comparable conditions.