Characterization and device physics of polymer semiconducting devices with metal oxide contacts

This thesis describes the fabrication and characterization of organic electronic devices with metal oxide contacts. The metal oxides focused on are zinc oxide and vanadium pentoxide. Low-temperature methods for layer deposition of the metal oxides are explored to make them compatible with the organic semiconductors, which are sensitive to high temperatures. The device characteristics of organic light-emitting diodes and different types of organic solar cells with these contacts are investigated. It is shown that the key performance characteristics of the different types of devices are equivalent to devices with a more conventional contact structure. On top of that the metal oxide contacts are more resistant to degradation under normal atmospheric conditions than reactive metals usually employed as cathode material. Classical equations for the diffusion current in semiconductor devices are adapted to the specific boundary conditions of contacts to organic semiconductors. Specifically the role of the Gaussian density of states in organic semiconductors and the assignment of a barrier height in the case of a non-ohmic contact to the organic semiconductor are discussed. These results are then used to derive an equation for the injection current density from a non-ohmic contact into an organic semiconductor. These equations for the diffusion and injection current densities in organic semiconductors are experimentally verified for a variety of materials and device structures.