Substitution of Ethynyl-Thiophene Chromophores on Ruthenium Sensitizers: Influence on Thermal and Photovoltaic Performance of Dye-Sensitized Solar Cells
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(C4H9)4), MC101” was synthesized and fully characterized by 1H-NMR, ESI-MASS, FT-IR, UV-Vis., and fluorescence spectroscopes. The dye showed relatively high molar extinction coefficient of 25.0 × 103？M？1 cm？1 at maximum of 544？nm, while the reference C101 has shown 15.8 × 103？M？1cm？1 at 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？cm2 active area TiO2 electrodes and high efficient electrolyte (E01), from the sensitizers MC101 and C101 exhibited energy conversion efficiencies of 3.25% (short-circuit current density ( ) = 7.32？mA/cm2, = 610？mV, ff = 0.725) and 2.94% ( = 6.60？mA/cm2; = 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 energy 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 photovoltaics, 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 compromise between efficiency and high temperature stability has been noted for the Z907 sensitizer [13]. For commercial applications of DSSCs, it
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