Daniel E. Acevedo Cartagena
Solution-based crystallization of conjugated polymers offers a scalable and attractive route to develop hierarchical structures for electronic devices. The introduction of well-defined nucleation sites into metastable solutions provides a way to regulate the crystallization behavior, and therefore the morphology of the material. I established a method focused on metastable solutions of poly(3-hexylthiophene) (P3HT). These metastable solutions allow P3HT to selectively crystallize into nanowires (NWs) on graphene-coated surfaces. It was found that the crystallization kinetics are faster with increasing P3HT molecular weight and concentration. Through in situ atomic force microscopy, I confirmed that nanowires grow vertically in a face-on orientation (i.e. the pi orbitals parallel to the substrate normal) from highly oriented pyrolytic graphite and graphene. However, as confirmed by X-ray scattering and scanning electron microscopy the face-on oriented crystals transitions from a face-on to an edge-on orientation (i.e. the _ orbitals perpendicular to the substrate normal) as the film grew thicker. Moreover, the transistors prepared by selectively crystallizing P3HT on graphene electrodes showed a film mobility two orders of magnitude higher than their spin-casted equivalents.