Donor-acceptor photovoltaic polymers based on 1,4-dithienyl-2,5-dialkoxybenzene with intramolecular noncovalent interactions

Donor-acceptor (D-A) conjugated polymers bearing non-covalent configurationally locked backbones have a high potential to be good photovoltaic materials. Since 1,4-dithienyl-2,5-dialkoxybenzene (TBT) is a typical moiety possessing intramolecular S...O interactions and thus a restricted planar configuration, it was used in this work as an electron-donating unit to combine with the following electron-accepting units: 3-fluorothieno[3,4-b]thiophene (TFT), thieno-[3,4-c]pyrrole-4,6-dione (TPD), and diketopyrrolopyrrole (DPP) for the construction of such D-A conjugated polymers. Therefore, the so-designed three polymers, PTBTTFT, PTBTTPD, and PTBTDPP, were synthesized and investigated on their basic optoelectronic properties in detail. Moreover, using [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as acceptor material, polymer solar cells (PSCs) were fabricated for studying photovoltaic performances of these polymers. It was found that the optimized PTBTTPD cell gave the best performance with a power conversion efficiency (PCE) of 4.49%, while that of PTBTTFT displayed the poorest one (PCE=1.96%). The good photovoltaic behaviors of PTBTTPD come from its lowest-lying energy level of the highest occupied molecular orbital (HOMO) among the three polymers, and good hole mobility and favorable morphology for its PC71BM-blended film. Although PTBTDPP displayed the widest absorption spectrum, the largest hole mobility, and regular chain packing structure when blended with PC71BM, its unmatched HOMO energy level and disfavored blend film morphology finally limited its solar cell performance to a moderate level (PCE: 3.91%). (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 689-698