Hindawi Publishing Corporation Advances in OptoElectronics Volume 2012, Article ID 482074, 10 pages doi:10.1155/2012/482074 Research Article Substitution of Ethynyl-Thiophene Chromophores on Ruthenium Sensitizers: Influence on Thermal and Photovoltaic Performance of Dye-Sensitized Solar Cells Malapaka Chandrasekharam, 1 Ganugula Rajkumar, 2 Thogiti Suresh, 1 and Paidi Yella Reddy 2 1 Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500 607, India 2 Aisin Cosmos R&D Co. Ltd, Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500 607, India Correspondence should be addressed to Malapaka Chandrasekharam, csmalapaka@yahoo.com Received 30 April 2011; Accepted 10 October 2011 Academic Editor: Surya Prakash Singh Copyright © 2012 Malapaka Chandrasekharam et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A new high molar extinction coefficient ruthenium(II) bipyridyl complex, “Ru(2,2-bipyridine-4,4 ′ -dicarboxylic acid)(4,4 ′ -bis((3- hexylthiophen-2-yl)ethynyl)-2,2 ′ -bipyridine)(NCS) 2 (N(C 4 H 9 ) 4 ), MC101” was synthesized and fully characterized by 1 H-NMR, ESI-MASS, FT-IR, UV-Vis., and fluorescence spectroscopes. The dye showed relatively high molar extinction coefficient of 25.0 × 10 3 M −1 cm −1 at λ maximum of 544 nm, while the reference C101 has shown 15.8 × 10 3 M −1 cm −1 at λ maximum 528 nm. The monochromatic incident photon-to-collected electron conversion efficiency of 44.1% was obtained for MC101 over the entire visible range, while the C101 sensitized solar cell fabricated and evaluated under identical conditions exhibited 40.1%. The DSSCs fabricated with 0.54 cm 2 active area TiO 2 electrodes and high efficient electrolyte (E01), from the sensitizers MC101 and C101 exhibited energy conversion efficiencies of 3.25% (short-circuit current density (J SC ) = 7.32 mA/cm 2 , V OC = 610 mV, ff = 0.725) and 2.94% (J SC = 6.60 mA/cm 2 ; V OC = 630 mV; ff = 0.709), respectively, under air mass of 1.5 sunlight. 1. Introduction Photovoltaic (PV) cells generating clean electricity are now getting ready for significant market expansion in this new millennium, as the solar energy is the major renewable ener- gy source and the major alternative to the fast depleting and polluting fossil fuels [1]. In the past decades, low-cost excitonic solar cells attracted worldwide attention among academic and industrial players as potential candidates for the future PV market [2]. Among this class of organic pho- tovoltaics, the mesoscopic dye-sensitized solar cell [3–5] (DSSC) has achieved a respectable high-efficiency [6, 7] and a remarkable stability under the prolonged thermal and light-soaking dual stress [8–12]. The record efficiency of ∼11% [6, 7] in DSSCs measured under the air mass 1.5 global (AM 1.5 G) illumination is achieved with the well- known N719 sensitizer employing a volatile acetonitrile- based electrolyte. However, stability under prolonged heating at 80 ◦ C has proved too hard to reach with the high-efficiency N719-based cells. In 2003, a thermally stable, ∼7% efficiency DSSC [9] was disclosed, employing the amphiphilic Z907 sensitizer [8] and a 3-methoxypropionitrile-(MPN-) based electrolyte avoiding lithium salts as additives. However, the molar extinction coefficient of this sensitizer is somewhat lower than that of the standard N719 dye. Meanwhile, a com- promise between efficiency and high temperature stability has been noted for the Z907 sensitizer [13]. For commercial applications of DSSCs, it is necessary to employ nonvolatile or even solvent-free electrolytes. However, with a low- fluidity electrolyte, the charge collection yield becomes low due to the shortened electron diffusion length. Enhancing the optical absorptivity of a stained mesoporous film can counter this effect. Thus, Wang et al. initiated the concept of developing high molar extinction coefficient, amphiphilic ruthenium sensitizer, [14] followed by other groups, [15–20] with a motivation to enhance device efficiency of DSSCs. In