Thin films of poly(3-hexylthiophene) (P3HT) are promising candidates for next generation of organic based electronic devices. Chain packing and crystallinity in such films have been shown to strongly affect their electronic and optical properties. Recently, confinement of thin semiconducting films have received a lot of interest, but there is still little known about the effect of nano-scale confinement and how its geometry affects crystallization in P3HT (REFS).
Here, we present results on how the geometry of true nano-confinement (2D vs. 3D) influences crystallization and the final crystallinity in P3HT films. Thin P3HT films were either confined between two solid walls (2D), or in a three-dimensional cylinder (3D) resulting in free standing nanoscale cylinders. The films were characterized by 2D synchrotron grazing incidence X-ray diffraction (2D GIXD) and by atomic force microscopy (AFM).
The results show a strong effect of the geometry of the confinement, and a different crystalline orientation between 2D and 3D confined films. Annealing time was also shown to strongly affect crystallinity, but in a different way compared to traditionally spun and annealed P3HT films. We discuss the effect of sample preparation, temperature and annealing time on crystallinity of P3HT in thin layers under confinement, and compare it to the crystallinity in non-confined thin films.