Synthesis and Photovoltaic Properties of Conjugated Copolymers with Benzo[1,2-b:4,5-b′]dithiophene and Bis(thiophene)phthalimide Units

Two new donor/acceptor copolymers PBDTPhBT1 and PBDTPhBT2 with alternating benzodithiophene (BDT) and bisthiophene-phthalimide (PhBT) units were synthesized by Stille coupling reaction. The copolymers showed identical optical bandgaps of 1.98 eV. The HOMO energy levels are -5.35 and -5.32 eV for PBDTPhBT1 and PBDTPhBT2, respectively. The bulk heterojunction solar cell devices based on these copolymers as donors and PC71BM as acceptor displayed high open-circuit voltages of 0.90-0.93 V and achieved power conversion efficiency of 1.54% under the illumination of AM 1.5, 100 mW.cm-2