A new high molar extinction coefficient organic-ruthenium(II) polypyridyl complex sensitizer (RD-Cou) that contains 2, ,6, -tetramethyl-9-thiophene-2-yl-2,3,5,6,6a,11c-hexahydro1H,4H-11oxa-3a-aza-benzoanthracene-10-one as extended -conjugation of ancillary bipyridine ligand, 4, -dicaboxy-2, , -bipyridine, and a thiocyanate ligand in its molecular structure has been synthesized and completely characterized by CHN, Mass, 1H-NMR, UV-Vis, and fluorescence spectroscopies as well as cyclic voltammetry. The new sensitizer was tested in dye-sensitized solar cells using a durable redox electrolyte and compared its performance to that of standard sensitizer Z-907. 1. Introduction The increasing demand for power supply as well as environmental concern for the consumption of fossil fuel have triggered a greater focus all over the world on renewable energy sources over the past decades [1]. In this context, solar energy appears to be very attractive alternate: covering 0.16% of the earth with 10% efficient solar conversion systems would provide power nearly twice the world’s consumption rate of fossil energy [2]. For this reason, dye-sensitized solar cells (DSSC) have emerged as one of the most promising candidates because of its cost-effective manufacturing, a respectable high efficiency and a remarkable stability under the prolonged thermal and light soaking dual stress among various photovoltaics [3–5]. A typical DSSC system consists of a nanocrystalline semiconductor that adsorbs a sensitizer on its surface, a Pt-counter electrode, and a redox mediator. The photosensitizer plays a crucial role in achieving higher photoconversion efficiency and has been actively studied globally. A wide variety of sensitizers have been studied for DSSC that includes various metal complexes, organic molecules, porphyrins, and phthalocyanines and so forth [6–9]. But only ruthenium-based sensitizers could have marked their way towards commercialization because of their high photoconversion efficiencies. The most successful ruthenium charge transfer sensitizers employed in such cells are bis(tetrabutylammonium)-cis-di(thiocyanato)-N,N′-bis(4-carboxylato-4′-carboxylic acid-2,2′-bipyridine)ruthenium(II) (the N719 dye) and trithiocyanato 4,4′4′′-tricaboxy-2,2′:6′,2′′-terpyridine ruthenium(II) (the black dye) produced solar-energy-to-electricity conversion efficiencies of >11% [10–13]. The high efficiency of these complexes are attributed to its suitable ground- and excited-state energy levels with respect to the nanocrystalline TiO2 conduction band energy and matching redox properties
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