Novel conjugated copolymers containing tetrafluorophenylene unit have been synthesized and evaluated in bulk heterojunction solar cell. The tetrafluorophenylene unit, as the strong electron deficient moeity, has been applied for the syntheses of donor-acceptor type copolymers with a narrow-band-gap for bulk heterojunction solar cells. DTBT, tetrafluorophenylene and four types of BDT derivatives as the electron rich units were incorporated using Stille polymerization to generate PE-BDTF, PO-BDTF, PE-BDTTF and PO-BDTTF. The introduction of even 1% of tetrafluorophenylene unit substituting DTBT of BDTDTBT type of polymers results in significant decrease of the band gap of the polymers. The device with PO-BDTF: PC71BM (1:1) showed an open-circuit voltage (V-OC) of 0.75 V, a short circuit current (J(SC)) of 11.80 mA/cm(2), and a fill factor (FF) of 0.59, which yields PCE of 5.22%. (C) 2015 Elsevier Ltd. All rights reserved.