Benzodifuran-containing well-defined pi-conjugated polymers for photovoltaic cells

Two well-defined alternating p-conjugated polymers containing a soluble electroactive benzo[1,2-b:4,5-b']difuran (BDF) chromophore, poly(BDF-(9-phenylcarbazole)) (PBDFC), and poly(BDF-benzothiadiazole) (PBDFBTD) were synthesized via Sonogashira copolymerizations. Their optical, electrochemical, and field-effect charge transport properties were characterized and compared with those of the corresponding homopolymer PBDF and random copolymers of the same overall composition. All these polymers cover broad optical absorption ranges from 250 to 750 nm with narrow optical band gaps of 1.782.35 eV. Both PBDF and PBDFBTD show ambipolar redox properties with HOMO levels of -5.38 and -5.09 eV, respectively. The field-effect mobility of holes varies from 2.9 x 10-8 cm2 V-1 s-1 in PBDF to 1.0 x 10-5 cm2 V-1 s-1 in PBDFBTD. Bulk heterojunction solar cell devices were fabricated using the polymers as the electron donor and [6,6]-phenyl-C61-butyric acid methyl ester as the electron acceptor, leading to power conversion efficiencies of 0.240.57% under air mass 1.5 illumination (100 mW cm-2). These results indicate that their band gaps, molecular electronic energy levels, charge mobilities, and molecular weights are readily tuned by copolymerizing the BDF core with different p-conjugated units. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012