In recent years a new class of electronics based on organic molecules or polymers has appeared on the market. Most prominent examples here are of course organic light emitting devices (OLEDs), which found use in screen and lighting technologies, but also organic field effect transistors (OFETs) and even organic solar cells (OSCs) are found in more and more applications. The potential advantages of a technology mainly based on organic molecules are numerous, ranging from lower production costs compared to rare earth containing inorganic solids, to novel material properties allowing e.g. for flexible devices. Unfortunately, the mechanisms governing charge transport are not at all well defined, making them hard to tackle computationally. At the same time, interactions at interfaces e.g. between organic crystals and metallic electrode materials as well as charge transport across these interfaces are poorly understood. Furthermore, theoretical studies here tend to be hampered by the large system sizes and computationally intensive methods needed to accurately describe charge transport. A major part of our work is therefore devoted to the development of efficient, yet accurate methods to simulate the movement of charge carriers in organic semiconductors as well as across metal/molecule interfaces. Based on these methods we estimate so-called descriptors, computationally undemanding properties of system that are correlated with a quantity of interest, such as the charge carrier mobility. These we apply in large scale screening studies to generate databases materials properties for the extraction of structure function relationships and thus rules for the potential design of efficient organic semiconductors.