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Orientation of organic semiconductors by an electric field
The ability to control crystallization for easier and cheaper fabrication is technologically important in many fields e.g. in pharmacy, food industry. Interaction with an electric field would be one method, since one can vary the electric field strength as well as the direction of the electric field. This talk will provide insight into the interaction of organic molecules with an electric field, generated with direct voltage, and how they crystallize in this environment. The experiments are performed by crystals formed at a substrate. Thin films are prepared by physical vapour deposition (PVD) and subsequently treated by solvent vapour annealing (SVA). Three different molecules (Ph-BTBT-10, Ph-BTBTOx2 and quinquethiophene) are used in combination with an interdigitated electrode structure providing a distance between the electrodes in the range of 10 μ up to 200 μ. Gold and ITO electrodes are used. For the SVA experiment two different solvents are used for a better statistical evaluation. These experiments we evaluate with Atomic Force Microscopy, Optical Microscope, X-Ray Refraction and with Grazing Incidence X-ray Diffraction. We found that an electric field reduces the nucleation density for crystallization which is predicted from theory and already experimentally confirmed. Additionally, we found that the crystals are formed at the edges of the electrodes with strong preferred orientation of the organic crystals. However, this second observation cannot be unambiguously referred to the impact of the electric field to the crystallization process.