Optical Characterization of Pristine Poly(3-Hexyl Thiophene) Films

We describe a comprehensive model for the optical properties of pristine films of poly-(3-hexylthiophene) (P3HT). The presented model is anisotropic with the optical axis normal to the substrate plane, which is consistent with previous x-ray diffraction studies that show preferential edge-on packing of the polymer chains on the substrate. Peak locations and spacings are defined using a Huang-Rhys vibronic progression consistent with known phonon energies. We demonstrate that the model fits variable-angle spectroscopic ellipsometry and normal-incidence transmission data well, and accurately predicts angle- and polarization-dependent transmission and reflection data. The spectral features of the optical constants used in the model are in excellent agreement with published spectroscopic data on P3HT.