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 cm 2 V –1 s –1 for PTTBT14 compared to 0.02 cm 2 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 61 BM, showing the poor photovoltaic characteristics.