| Organic semiconductors have received increased interest over the last sixteen to seventeen years due to their potential applications in optical and electronic devices such as flexible displays, radio frequency identification tags, and solar cells. Attractive characteristics of organic semiconductor thin films include mechanical flexibility and suitability for low-temperature processing. At present, however, many fundamental questions are still unanswered about the nature of charge transport mechanism at metal/organic or organic/organic interfaces, and how the interface properties affect the performance of organic electronics.; This thesis describes the research undertaken in the field of interfaces in organic electronic devices. Specially, metal/organic interfaces and organic/organic interfaces are investigated. It is well known that the properties of metal/organic contacts are of great importance to organic electronics. In this research the systematic investigation of current-voltage characteristics ( J-V) and contact barrier heights for different metal contacts to organic films are performed. The geometry of the devices consisted of a metal contact deposited on a thermally evaporated organic film on a conductive indium tin oxide (ITO) substrate. Contact barrier heights are extracted by a combination of J-V and activation energy measurements over the temperature range 120-340 K. Transport through the devices is modeled in terms of the balance between thermally activated carrier injection at the metal/pentacene contact and the interface recombination current.; To investigate the effect of organic/organic interfaces at open-circuit voltage of bi-layer organic solar cells, a series of organic photovoltaic (PV) cells have been fabricated, with the configuration ITO/oligoacene (pentacene, tetracene and rubrene)/C60/1n:Ga. Oligoacene is a hole-conductor and acts as an electron donor (D) while C60 corresponds to an acceptor (A). This experiment is designed to study how the energy level mismatch between D/A materials influences the open-circuit voltage of the PV cell. The D/A heterojunction PV cells with different donor materials were examined under AM 1.5 spectral illumination of 100 mW/cm2.; Electrical characterization is carried out with high-impedance electrometers in air and in a high-vacuum probe station. The organic thin-films are characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD) to determine crystal structure parameters and phase composition. |
