Semicrystalline D-A copolymers with different chain curvature for applications in polymer optoelectronic devices

Thiophene- and thienothiophene-based donor-acceptor (D-A) type semicrystalline copolymers with different backbone curvatures, PTBT14 and PTTBT14, were designed and synthesized. Both the polymers exhibit a nearly planar structure via noncovalent S···O and C-H···N attractive interactions, etc., in the polymer chain. PTTBT14 is linear, whereas PTBT14 is curved owing to ∼160° bond angle of the thiophene linkage. PTTBT14 showed the higher degree of interchain ordering with edge-on orientation, resulting in efficient charge transport (0.26 cm² V^-1 s^-1 for PTTBT14 compared to 0.02 cm² V^-1 s^-1 for PTBT14) in PFETs with remarkable morphological stability and no deterioration in device properties at temperatures up to 250 °C. On the other hand, the curved shape of PTBT14 attributed to its improved photovoltaic properties with a power conversion efficiency of 5.56%. The linear PTTBT14 showed much stronger self-interactions with negligible morphological changes and little miscibility with PC ₆₁BM, showing the poor photovoltaic characteristics.