Understanding the Structure and Crystallization of Regioregular Poly (3-hexylthiophene) from the Perspective of Epitaxy

Conjugated polymers form a remarkable class of macromolecules with fascinating electronic properties as well as structural features that make them very different from the more classical and flexible polyolefins. In thin films, the structure and the nanomorphology are two important parameters that control solid state properties such as charge transport. Due to the high anisotropy of electronic properties in conjugated polymers, it is essential to control both crystallization and domain orientation over large length scales. This review demonstrates that epitaxial growth is an original method for bringing macromolecules like regioregular poly(3-hexylthiophene) (P3HT) to a high level of order. Various orientation methods based on epitaxy are presented and the peculiar morphological and structural aspects of oriented P3HT, as analyzed by transmission electron microscopy (TEM), are described. The use of TEM on epitaxied layers is shown to shed some new light on the intriguing crystallization, structure, and growth of this key polymer for organic electronic applications.