Optical dispersion and dielectric properties of rubrene organic semiconductor thin film

Rubrene thin film has been fabricated on a glass substrate by spin-coating at 300 K. The optical dispersion and dielectric properties of the film have been determined from the analysis of transmittance and reflectance measurements at normal incident of light between 200 and 700 nm. The optical transmittance of the film was estimated as of 80–85 % in the visible range. Optical absorption characteristics show that the absorption mechanism is due to the indirect transition. The transport and onset optical energy gaps were determined as 2.93 and 2.31 eV, respectively. Single term Sellmeier dispersion relation and Wemple–DiDomenico single oscillator model were used to determine the optical dispersion parameters. Several dispersion parameters such as lattice dielectric constant, optical dielectric constant at higher frequency, dispersion energy, oscillator energy, the ratio of carrier concentration to the effective mass, the average oscillator wavelength, and average oscillator strength were determined by analysis of refractive index dispersion. The loss factor, the electric modulus, the optical conductivity, the volume and surface energy loss functions, and the relaxation time were also evaluated from the optical dielectric constants analysis.