Bis(2-oxoindolin-3-ylidene)-benzodifuran-dione-based D–A polymers for high-performance n-channel transistors†
Conjugated polymers based on a bis(2-oxoindolin-3-ylidene)-benzodifuran-dione (BIBDF) unit displayed promising performances for their application in organic thin-film transistors (OTFTs). Herein, three new BIBDF-based donor–acceptor (D–A) polymers, containing thieno[3,2-b]thiophene (TT), (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TVT) and (2-(thiophene-2-yl)alkynyl)thiophene (TAT) as donors, were synthesized and characterized. The results indicated that the donor unit plays important roles in affecting the absorption bands, HOMO levels, lamellar packing and π–π stacking distances of the BIBDF-based polymers. The OTFT devices based on the three polymers were fabricated, and their field-effect performance and environmental stability were also characterized. All three BIBDF based polymers showed good n-type field-effect characteristics. The PBIBDF-TT showed the highest electron mobility of 0.65 cm2 V−1 s−1 and the best environmental stability, while the PBIBDF-TAT showed the lowest electron mobility of 0.13 cm2 V−1 s−1. The corresponding crystalline structures and morphologies revealed that the PBIBDF-TT and PBIBDF-TVT showed close π–π distances and long-range ordered, lamellar crystalline structures both of which contributed to the high charge carrier mobility. The PBIBDF-TAT with close π–π distances but poor crystalline structures showed miserable performance. Overall, this work showed the correlation of the microstructures and properties of BIBDF-based polymers, and the field-effect performances can be effectively optimized by introducing different donor units.