Steve Pittner

• Organic semiconductors reveal charge transport properties, which can not be explained with standard models of inorganic semiconductors. In this PhD thesis, electroreflectance (ER) spectroscopy is used to investigate optically charge transport processes in organic semiconductor thin films, in order to achieve detailed information of the accumulation layer close to the insulator-organic semiconductor interface. This technique probes the reflectance changes due to an altered charge density within the organic semiconductor. The reflectance geometry offers the possibility to investigate samples with optically opaque substrates. Optical simulations of layer stacks were used to determine quantitatively changes of the dielectric function due to charge injection into the accumulation layer of a poly(3-hexylthiophene) (P3HT) thin film. The spin-coated layers of P3HT revealed an anisotropic dielectric function, as found with spectroscopic ellipsometry. Furthermore, ER data of three samples with altered insulator-organic semiconductor interfaces are analyzed with the developed theoretical approach. Characteristic spectral changes were found in laterally resolved measurements depending on the insulator-organic semiconductor interface. Significant distance-dependent spectral changes indicate a time-dependent relaxation process after charges have been injected from a Au electrode.