High hole mobility from thiophene-thienopyrazine copolymer based thin film transistors

Surface morphologies and thin film transistor characteristics of three thiophene (TH)-thieno[3,4-b]pyrazine (TP) donor-acceptor conjugated copolymers (PTHTP-C7, PTHTP-C12, and PBTHTP-C7) are reported. The long alkyl side chain probably promoted PTHTP-C12 to become a fibrillar-like structure on the hexamethyldisilazane (HMDS)-modified surface and resulted in better charge transport properties than the other two copolymers. However, a nodule-like morphology on the octyltrichlorosilane (OTS)-modified surface was observed due to the strong interaction between the non-polar alkyl chains of PTHTP-C12 and highly hydrophobic surface. By further annealing at a higher temperature, a densely packed grain morphology on octyltrichlorosilane (OTS) modified SiO2 surface was shown and led to the field effect mobility of 1.1 x 10(-2) cm(2) V-1 s(-1) with the on/off ratio of 227. The present study suggests that thiophene based donor-acceptor conjugated polymers could have a high FET mobility through the manipulation of polymer morphology.