Thickness dependence of surface morphology and charge carrier mobility in organic field-effect transistors

With the aim of understanding the relationships betweenorganic small molecule field-effect transistors (FETs) and organicconjugated polymer FETs, we investigate the thickness dependence ofsurface morphology and charge carrier mobility in pentacene andregioregular poly (3-hexylthiophene) (RR-P3HT) field-effecttransistors. On the basis of the results of surface morphologies andelectrical properties, we presume that the charge carrier mobilityis largely related to the morphology of the organic active layer. Weobserve that the change trends of the surface morphologies (averagesize and average roughness) of pentacene and RR-P3HT thin films aremutually opposite, as the thickness of the organic layer increases.Further, we demonstrate that the change trends of the field-effectmobilities of pentacene and RR-P3HT FETs are also opposite to eachother, as the thickness of the organic layer increases within itslimit.