Naphthobisthiadiazole-Based Selenophene-Incorporated Quarterchalcogenophene Copolymers for Field-Effect Transistors and Polymer Solar Cells

In this research, we developed six new selenophene-incorporated naphthobisthiadiazole-based donor–acceptor polymers PNT2Th2Se-OD, PNT2Se2Th-OD, PNT4Se-OD, PNT2Th2Se-DT, PNT2Se2Th-DT, and PNT4Se-DT. The structure–property relationships have been systematically established through the comparison of their structural variations: (1) isomeric biselenophene/bithiophene arrangement between PNT2Th2Se and PNT2Se2Th polymers, (2) biselenophene/bithiophene and quarterselenophene donor units between PNT2Th2Se/PNT2Se2Th and PNT4Se polymers, and (3) side-chain modification between the 2-octyldodecylthiophene (OD)- and 2-decyltetradecyl (DT)-series polymers. The incorporation of selenophene units in the copolymers induces stronger charge transfer to improve the light-harvesting capability while maintaining the strong intermolecular interactions to preserve the intrinsic crystallinity for high carrier mobility. The organic field-effect transistor device using PNT2Th2Se-OD achieved a high hole mobility of 0.36 cm 2 V –1 s –1 with an on/off ratio of 1.9 × 10 5 . The solar cells with PNT2Th2Se-OD:PC 71 BM exhibited a power conversion efficiency of 9.47% with a V oc of 0.68 V, an fill factor of 67%, and an impressive J sc of 20.69 mA cm –2 .