Accurate Polarization-Resolved Absorption Spectra of OrganicSemiconductor Thin Films Using First-Principles Quantum-ChemicalMethods: Pentacene as a Case Study

Theoretical studies using clusters as model systems have been extremelysuccessful in explaining various photophysical phenomena in organic semiconductor (OSC)thinfilms. But they have not been able to satisfactorily simulate total and polarization-resolvedabsorption spectra of OSCs so far. In this work, we demonstrate that accurate spectra arepredicted by time-dependent density functional theory (TD-DFT) when the employed clusterreflects the symmetry of the crystal structure and all monomers feel the same environment.Additionally, long-range corrected optimal tuned functionals are mandatory. For pentacenethinfilms, the computed electronic spectra for thinfilms then reach an impressive accuracycompared with experimental data with a deviation of less than 0.1 eV. This allows for accuratepeak assignments and mechanistic studies, which paves the way for a comprehensiveunderstanding of OSCs using an affordable and easy-to-use cluster approach.