Organic semiconductors experience increasingly applications in modern electronics due to their cheap manufacturing and their special properties like, e.g., flexibility. In general these applications require an efficient charge transport, which is investigated here using the example of the polymer P3HT. Thereby, the focus is on the identification of strongly transport limiting structural defects. These defects are modeled by a variety of configurations for which the properties are determined in the framework of the density functional theory. An adsorption of oxygen to a polymer strands carbon backbone as well as torsion angles around 90 between two adjacent P3HT monomers are found to strongly reduce the conductivity.A strong coupling between ionic and electronic degrees of freedoms enables interesting physical and technological relevant effects. Therefore, the analysis of such couplings constitutes the main part in the following considerations. The electron-phonon coupling in P3HT is accounted for by introducing the polaron quasiparticle, which enables also a temperature-dependent transport description. Since modern processings exploit increasingly the particular properties of nanomaterials like, e.g., quantum dots and nanowires, the last part of the thesis deals with indium nanowires on a silicon surface. The representative focus is here on the theoretical description of an experimentally observed optically driven phase transition. This transition is characterized by strongly coupled, time-dependent ion and electron dynamics. The microscopic details of the phase transition are elucidated and the results are, e.g., additionally visualized by a detailed bonding analysis. The predicted phase transition time constants are thereby in good agreement with the experimental measurements.