Synergistic effect of polymer and oligomer blends for solution-processable organic thin-film transistors

The thin-film morphologies and thin-film transistor (TFT) characteristics of a series of binary blends of poly(9,9′-dioctylfluorene-alt-bithiophene) (F8T2) and α,ω-dihexylquarterthiophene (DH4T) are reported. The blends of F8T2 and DH4T exhibit good solubility and produce TFT devices with better performances than F8T2 and DH4T devices. The 50% DH4T blend device was found to have a hole mobility of 0.011 cm 2 V−1 s−1, which is four times higher than the mobility of the F8T2 device, with a high-on/off ratio of about 105 and a low-off current of 17 pA. The polymer and oligomer domains are phase-separated with large domain size and arranged in characteristic molecular alignments. It was found that carrier transport in the blend systems is mainly controlled by the polymer component, and that the nature of the blended oligomer affects the OTFT performance of the blends.