Dielectric function and one-dimensional description of the absorption of poly(3-octylthiophene)

Abstract We have studied the optical properties of poly(3-octylthiophene) (P3OT) thin films, prepared by spin coating, with variable angle spectroscopic ellipsometry (SE). The off-diagonal elements of the reflection matrix have been analysed revealing that the films are optically anisotropic with the optical axis normal to the sample surface, which is a result of the orientation of the polymer chains parallel to the surface. By simultaneously fitting ellipsometric spectra of the samples, both parallel and perpendicular components of the dielectric function were obtained. The imaginary parts of both components show a strong optical anisotropy (7:1). In addition, a one-dimensional density of states model was used to describe the frequency dispersion of the imaginary part of dielectric function in the high-energy region. An excellent agreement with experiment was found, leading to a fundamental band gap of 2.67 eV.