High-Performance Hole Transport and Quasi-Balanced Ambipolar OFETs Based on D-A-A Thieno-benzo-isoindigo Polymers

Two new conjugated polymers are synthesized based on a novel donor-acceptor-acceptor (D-A-A) design strategy with the intention of attaining lower lowest unoccupied molecular obital levels compared to the normally used D-A strategy. By coupling two thieno-benzo-isoindigo units together via the phenyl position to give a new symmetric benzene-coupled di-thieno-benzo-isoindigo (BdiTBI) monomer as an A-A acceptor and thiophene (T) or bithiophene (2T) as a donor, two new polymers PT-BdiTBI and P2T-BdiTBI are synthesized via Stille coupling. The two polymers are tested in top gate and top contact field effect transistors, which exhibit balanced ambipolar charge transport properties with poly(methyl methacrylate) as dielectric and a high hole mobility up to 1.1 cm(2) V-1 s(-1) with poly(trifluoroethylene) as dielectric. The polymer films are investigated using atomic force microscopy, which shows fibrous features due to their high crystallinity as indicated by grazing incidence wide-angle X-ray scattering. The theoretical calculations agree well with the experimental data on the energy levels. It is demonstrated that the D-A-A strategy is very effective for designing low band gap polymers for organic electronic applications.
Funding Agencies|Swedish Research Council; Swedish Energy Agency; EU projects SUNFLOWER "SUstainable Novel FLexible Organic Watts Efficiently Reliable" [FP7-ICT-2011-7, 287594]; National Natural Science Foundation of China [21504066]; Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]