Highly Oriented and Nanotextured Films of Regioregular Poly(3-hexylthiophene) Grown by Epitaxy on the Nanostructured Surface of an Aromatic Substrate

A simple method for the nanotexturing and orientation of regioregular poly(3-hexylthiophene) (P3HT) thin films has been developed. Epitaxial growth of P3HT on the surface of an aromatic salt (potassium 4-bromobenzoate) (K-BrBz) leads to highly oriented and nanotextured P3HT films which consist of a regular network of interconnected semicrystalline domains oriented along two preferential in-plane directions. The overall crystallinity and the level of in-plane orientation of the P3HT films are controlled by the temperature of isothermal crystallization (T-iso). Well-defined electron diffraction patterns with sharp reflections obtained for T-iso = 180 degrees C indicate that the crystalline domains grow with a unique (1 0 0) P3HT contact plane on the K-BrBz substrate with the P3HT chains oriented along the [0 +/- 2 1] K-BrBz directions of the substrate. During the annealing of the polymer film, the surface of the aromatic salt undergoes a topographic reconstruction resulting in a regular nanostructured "hill and valley" topography that templates and orients the growth of P3HT. Preferred orientation of P3HT crystalline domains occurs at step edges of the substrate and is favored by the matching between the layer period of P3HT and the terrace height of the K-BrBz substrate.