Novel wide band-gap polymer utilizing fused hetero-aromatic unit for efficient polymer solar cells and field-effect transistors

Novel wide band-gap polymer of PBTFT containing dibenzosexithiophene-alt-bithiophene backbone was designed and synthesized via the Stille cross-coupling reaction. This polymer exhibited good thermal stability, well coplanar backbone and a broad absorption band from 350 nm to 610 nm with a wide optical band-gap of 2.02 eV. The polymer solar cells (PSCs) based on the PBTFT:PC₇₁BM active layer showed the power conversion efficiency of 3.0% with an open circuit voltage of 0.70 V, a short-circuit current of 7.94 mA cm^-2 and a fill factor of 53.98% under the illumination of AM.1.5, 100 mW cm^-2. Holes mobility up to 0.028 cm² V^-1 s^-1 with an on-off ratio of 1.0 × 10⁶ was obtained in the PBTFT-based organic field-effect transistors (OFETs). Our work indicates that the dibenzosexithiophene-alt-bithiophene based copolymer can be efficiently applied in PSCs and OFETs.