Bis(2-oxoindolin-3-ylidene)-benzodifuran-dione-based D-A polymers for high-performance n-channel transistors

Abstract

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 pi-pi 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 cm(2) V-1 s(-1) and the best environmental stability, while the PBIBDF-TAT showed the lowest electron mobility of 0.13 cm(2) V-1 s(-1). The corresponding crystalline structures and morphologies revealed that the PBIBDF-TT and PBIBDF-TVT showed close pi-pi distances and long-range ordered, lamellar crystalline structures both of which contributed to the high charge carrier mobility. The PBIBDF-TAT with close pi-pi 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.