Bisfuran-s-Tetrazine-Based Conjugated Polymers: Synthesis, Characterization, and Photovoltaic Properties

Bisfuran-s-tetrazine (FTz) and its copolymers with cyclopenta[2,1-b: 3,4-b']dithiophene (CPDT) and benzo[1,2-b:4,5-b']dithiophene (BDT) (PCPDTFTz and PBDTFTz) are prepared with the alternating s-tetrazine and CPDT or BDT units bridged by a furan ring. Their optical and electro-chemical properties are studied and compared with their thiophene analogs (PCPDTTTz-out and PCPDTTTz-in), in which the bridging unit is 4-hexylthiophene or 3-hexylthiophene, respectively. Bulk heterojunction (BHJ) solar cells fabricated from these polymers with PC71 BM have a power conversion efficiency (PCE) of 0.8%, which is much lower than that from the PCPDTTTz-out analog (3.2%), due to the low steric hindrance of the furan polymers in the absence of alkyl substitution on the furan ring.