Green route to green energy: C-H activation of diflourinated benzothiadiazole as a dye creation for dye-sensitized solar cells

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Rojas, Anthony Jose
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Controlling sensitizer structures and synthetic routes for synthesis of dyes on a nanocrystaline TiO2 surface is important for facilitating charge transfer, limiting charge recombination, and reducing costs in organic solar cells. We successfully developed and employed C-H activation methods for 5,6-difluoro-2,1,3-benzothiadiazole to synthesize a dye, limiting the route to subsequent steps and reducing waste. Additionally, we substituted the commonly used π-bridge, thiophene, for a more aggregating-preventative cyclopentadithiophene with 2 hexyl groups flanking out of the conjugated plane to construct a novel D−A−π−A-featuring dye, AR-II-13. The dye had of several beneficial characteristics: (i) extended absorption bands to dyes of similar construct effectively decrease the HOMO-LUMO band gap; (ii) the elaborate structure efficiently limits the recombination of electrons in TiO2 and electrolyte. The dye-sensitized solar cell device created using AR-II-13 exhibited promising power conversion efficiency of up to 6.6 +/- 0.1%, based on preliminary findings, with a short-circuit current density (Jsc) of 12.7 mA cm−2, an open-circuit voltage (Voc) of 0.73 V, and a fill factor (FF) of 0.712 under AM 1.5 illumination (100 mW cm−2). The combination of each donor/acceptor moiety to the difluorinated benzothiadiazole bridge using C-H activation demonstrated the success possible in these types of reactions by producing high yields, even on unsymmetrical dyes. The successful C-H activation implementation on this type of molecule towards creating a functional unit is especially intriguing as it reduces waste and cost of materials.
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