Conjugated Polymer Chain and Crystallite Orientation\nInduced by Vertically Aligned\nCarbon Nanotube Arrays

Abstract

We\nreport a method for controlling the orientations of conjugated\npolymers in the active layer of organic thin-film transistors (OTFTs)\nby annealing the film at the melting temperature in a vertically aligned\nmultiwalled carbon nanotube (VA-CNT) template under various load pressures.\nPoly­(3-hexylthiophene) [P3HT] molecules are effectively aligned in\nthe melting state annealing at 240 °C for 30 min, as a result\nof intermolecular π–π and CH₃–π\ninteractions between the polymer and the VA-CNTs, which are separated\nfrom the conjugated polymer film after cooling to room temperature.\nIn-plane and out-of-plane X-ray diffraction results show that the\nmelt-annealed P3HT film with VA-CNTs has better crystallite ordering\nthan a pristine 80 °C baked film and a melt-annealed film without\nVA-CNTs, and a larger number of crystallites in the treated P3HT film\nare oriented in the [100] direction, which is normal to the substrate.\nWhen we used the melt-aligned P3HT film with VA-CNTs as the active\nlayer in OTFTs, the P3HT OTFT exhibits a better field-effect mobility\nvalue of 0.12 cm²/(V s) than a simply melt-annealed device\nwithout VA-CNTs [0.06 cm²/(V s)].