Mesoscopic disorder in thin film spectra: absorption spectroscopy of sexithiophene

In order to simulate disorder effects in thin films, model calculations of the absorption spectrum are performed for a statistical ensemble of differently oriented sexithiophene microcrystals. The assumed distribution of crystallite orientations is based on available experimental data. The directional dependence of the non-analytic part of dipole lattice sums is identified as the leading broadening mechanism; other contributions to broadening are also discussed.