LAUSR

The crystalline and morphological structures of polymer semiconducting films were controlled by selecting for appropriate thermal properties in the polymeric chains, thereby improving polymer FET performances. Poly(dioctyl-quaterthiophene-dioctyl-bithiazole) (PDQDB), comprising 5,5'-bithiazole and oligothiophene rings, was used as the basis for the polymer semiconductor studies. The Tg and Tm values of the thin film state, rather than of the bulk polymer state, were important in this study. A PDQDB film with a Tg of 101˚C in the thin film state showed the highest maximum and average μFET values, 0.194 and 0.141 cm2V-1s-1, respectively, in an FET device at a post-processed temperature of 100˚C. On the other hand, relatively low average μFET values of 0.115, 0.098, and 0.079 cm2V-1s-1 were observed in FET devices prepared from PDQDB films with Tg values of 130, 165, or 180˚C, respectively, despite the dramatic increases in film crystallinity. With the variations in the μFET, what we have noticed is that the standard deviations of the measured μFET values varied with the Tg values: 36.0% for the Tg = 165˚C film and 51.1% for the Tg = 180˚C, indicating that the OFET performances were not uniform. These results were closely related to nano- and microscale non-uniformity in the PDQDB film structure in the presence of excessively activated grain structures. These variations were correlated with the crystalline and morphological structures of the PDQDB films prepared under various processing conditions.