Side chain engineering of fluorinated benzothiadiazole-based polymers: Improving the charge transport in organic field-effect transistors

Three donor-acceptor (D-A) polymers P1–P3 are designed and synthesized, with 4,7-dibromo-5,6-difluorobenzo[c][1,2,5]thiadiazole (FBT) as A and thiophene derivatives as D. All polymers show good thermal stability. The UV–vis absorption spectra show that P1 has too strong aggregation in solution, and it has no obvious temperature-dependent aggregation (TDA) performance, which is also revealed in the variable temperature UV–vis absorption spectra. P2 film shows the same aggregation as in solution, P3 film shows stronger aggregation than that in solution. Polymers P1 and P2 both have strong TDA properties. Organic field effect transistors (OFETs) are prepared based on polymers P1, P2, and P3. OFETs devices prepared with high molecular weight polymers have better performance, and the polymer with 2-nonyltridecyl side chain leads to the highest hole mobility around 0.252 cm² V⁻¹ s⁻¹. The results show that the application of high molecular weight polymers and the selection of appropriate side chains are very important for the charge transport performance of OFETs.