Drastic Enhancement of X-ray Scattering Contrast between Amorphous and Crystalline Phases of Poly(3-hexylthiophene) at the Sulfur K-Edge

Semicrystalline semiconducting polymers such as poly(3-hexylthiophene) exhibit hierarchical molecular ordering that influences their optoelectronic properties. As well as possessing crystalline order on the molecular scale, P3HT also exhibits regular ordering of crystalline lamellae on the nanoscale. This layering of crystalline and amorphous regions is characterized by the so-called “long period” which can be measured with small-angle X-ray scattering (SAXS). The weak scattering contrast between amorphous and crystalline phases generally requires SAXS measurement of bulk powder samples. Here, we show that by utilizing polarized tender X-rays tuned to the sulfur K-edge, strong contrast between amorphous and crystalline phases can be generated allowing for the long period of thin film P3HT samples to be easily observed. Furthermore, we show that the contrast generated results from differences in orientational order in the amorphous and crystalline regions. The use of resonant tender X-ray scattering is thus a promising technique for studying nanoscale ordering not only in semiconducting polymers but also for other soft matter systems.