2,1,3-Benzooxadiazole, thiophene and benzodithiophene based random copolymers for organic photovoltaics: thiophene versus thieno[3,2-b]thiophene as π-conjugated linkers

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Three conjugated random copolymers comprising benzodithiophene and thiophene as the donor units and benzooxadiazole as the acceptor unit, spaced with thiophene and thieno[3,2-b]thiophene π-bridges, were designed and synthesized. The effects of different linkers on the optical and electrochemical properties were investigated. The polymer containing a thieno[3,2-b]thiophene π-bridge revealed a red shifted absorption compared to its thiophene analogue. Morphological and photovoltaic properties of a polymer:fullerene blend film were investigated. The blend of one of the random copolymers (P2) and PC71BM ([6,6]-phenyl-C71-butyric acid methyl ester) revealed a photovoltaic performance efficiency of 5.17% due to the high short-circuit current density and fill factor.