Thienothiophene-benzotriazole-based semicrystalline linear copolymers for organic field effect transistors

A series of thienothiophene-benzotriazole-based semicrystalline copolymers, PTTBTz, PTTBTz- F, and PTTBTz-OR, were synthesized by considering chain linearity, planarity and inter-chain packing by virtue of non-covalent attractive interaction. Fluorine and alkoxy substituents were introduced to modulate the intra- and inter-chain coulombic interactions and crystalline ordering. The fluorine and alkoxy-substituted PTTBTz-F and PTTBTz-OR showed pronounced inter-chain packing with edge-on orientation confirmed by UV-vs absorption and X-ray diffraction measurements. The well-resolved diffraction patterns were obtained for PTTBTz-F and PTTBTz-OR, showing (100)∼(500) inter-lamellar scattering peaks (d-spacing, 17∼18 Å) in the out-of-plane direction and a π-π stacking peak (d-spacing, 3.5∼4.1 Å) in the in-plane direction. Organic field effect transistor (OFET) devices were fabricated with a bottom gate and top contact geometry. PTTBTz-F (μ_h =4.49 ×10^-2cm² V^-1 s^-1, on/off ratio =1.13 ×10⁷) and PTTBTz-OR (μ_h =8.39 ×10^-3 cm2 V^-1 s^-1, on/off ratio =2.98 ×10⁴) showed nearly 3 and 2 orders of magnitude higher hole mobility upon annealing at 305 and 260 °C, with compared to the unsubstituted PTTBTz.