Novel Random Low-Band-Gap Fluorene-Based Copolymers for Deep Red/Near Infrared Light-Emitting Diodes and Bulk Heterojunction Photovoltaic Cells

Novel readily soluble random low‐band‐gap conjugated copolymers (PFO–DTTP, Eg ≈ 1.77–2.00 eV) derived from 9,9‐dioctylfluorene (DOF) and 2,3‐dimethyl‐5,7‐dithien‐2‐yl‐thieno[3,4‐b]pyrazine (DTTP) were prepared. The solutions and the solid thin films of the copolymers absorbed light from 300–690 nm. Prototype photovoltaic cells from solid state composite films with the copolymer PFO–DTTP30 and [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) showed power conversion efficiencies up to 0.83% under an AM1.5 solar simulator (100 mW · cm−2). For electroluminescent devices, the emission peaks were around 734–780 nm. This indicates that the low band gap copolymers are promising materials for polymeric solar cells and deep red/near infrared light‐emitting diodes. Synthesis of novel low‐band‐gap fluorene‐based copolymer.