Modeling of the photophysical properties of alpha-sexithiophene thin films

Photoluminescence spectral features of alpha-sexithiophene (alpha-T-6) thin films have been demonstrated to be directly linked to film morphology and temperature. Ultra-thin films at low temperature show vibronic resolved photoluminescence (PL) spectra typical of intrinsic excitonic emission. As film thickness increases, PL spectra show additional emission at low energy, which is attributed to trap states. The nature of the trap states is to date elusive as well as the non-radiative mechanism involving exciton and trap states. Here, we report a phenomenological model that allows to determine the photophysical rate constants of the excitonic and trap state transitions and the density of traps in alpha-T-6 thin films. Our model accounts for the thickness dependence of alpha-T-6 films optical emission and is well in agreement with the observed variation of photoluminescence as a function of temperature in the range of 4-300 K. (C) 2003 Elsevier Science B.V. All rights reserved.