Benzodifuran-Based π-Conjugated Copolymers for Bulk Heterojunction Solar Cells

Novel π-conjugated copolymers based on a soluble electroactive benzo[1,2-b:4,5-b′]difuran (BDF) chromophore have been synthesized by the introduction of thiophene/benzo[c][1,2,5]thiadiazole/9-phenylcarbazole comonomer units. These copolymers cover broad absorption ranges from 250 to 700 nm with narrow optical band gaps of 1.71−2.01 eV. Moreover, their band gaps as well as their molecular electronic energy levels are readily tuned by copolymerizing the BDF core with different π-conjugated electron-donating or withdrawing units in different ratios. Bulk heterojunction solar cell devices are fabricated using the copolymers as the electron donor and PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) as the electron acceptor. Preliminary research has revealed power conversion efficiencies of 0.17−0.59% under AM 1.5 illumination (100 mW/cm2).