It will be shown how first-principles calculations based on density functional theory contribute to an understanding of organic semiconductors, which form the active layers in electro-optical devices. To this extent, the intrinsic electronic and optical properties of the bulk materials will be discussed first. The latter are governed by strong excitonic effects and thus require the solution of the Bethe-Salpeter equation derived within manybody perturbation theory. The operation of a device like an OLED or an OFET is, however, also determined by the interface between a metal electrode and the organic semiconductor. In this context, the cohesive properties of the organic materials as well as their interfaces with metal surfaces are key quantities, where van der Waals interactions play the most important role. Finally, a controlled film growth also requires the determination of the relevant processes and the corresponding energy barriers. As a first example, we have investigated the energetics driving mound formation of sexiphenyl molecules on mica as revealed by atomic-force microscopy. Combining nucleation theory to analyze the measured data with transition state theory, a step edge barrier was deduced which, interestingly, turned out to be layer-dependent.
Host: Gabriel Kotliar