Record high mobilities for regioregular poly(3-octylthiophene)

Regioregular poly(3-alkylthiophene)s are promising candidates for plastic electronics. In particular, poly(3-hexylthiophene) (P3HT) has attracted considerable interest due to its excellent field effect mobility. However, not much attention has been given to poly(3-alkylthiophene)s with longer alkyl side chains, mainly because a few studies reported that longer side chain length was detrimental to field effect mobility. However, these past studies used untreated SiO2 as the gate dielectric and commercially available polymers synthesized by the Rieke method. Here, all polymers tested were synthesized in house using our quasi-living GRIM method to yield well-defined clean polymers. For our first study, we synthesized P3HT and regioregular poly(3-octylthiohene) (P3OT), both with a high molecular weight (Mn of 40kDa and 35kDa, respectively). Regioregular P3HT required some sonication to dissolve in chloroform, whereas P30T dissolved readily in chloroform at room temperature. Hole mobility was measured using bottom-contact geometry, with SiO2 as gate dielectric. The SiO2 surface was either untreated, or chemically treated with octyltrichlorosilane. Average mobility on untreated SiO2 was 0.09 cm(2)/VS for P3HT and 0.03 cm(2)/Vs for P3OT. Average mobility on OTS-8 treated SiO2, on the other hand, was 0.13 cm(2)/Vs for P3HT and 0.19 cm(2)/Vs for P3OT. The OTS-8 treatment therefore dramatically improved the mobility of P30T. Both polymers had a maximum mobility of about 0.2 cm(2)/Vs for channel lengths >= 10 mu m, and a mobility of 0.22 cm(2)/Vs was obtained several times for P3OT. To our knowledge, this is by far the highest mobility reported for P3OT.