In order to manufacture organic electronic devices with high performance, more detailed studies of the structure and the morphology of the organic materials as well as the underlying physical charge transport mechanisms are warranted. For instance, high efficiency organic thin film transistors (OTFTs) require materials with high charge carrier mobility [1, 2]. The parameters that determine the charge carrier mobility of the device include the structure of the first organic layer at the organic-dielectric interface as well as the morphology and the structural order of the other organic layers. Therefore, fundamental questions about structural properties of organic materials should be answered in order to optimize device performance [2-4]. In this work, several bilayer structures of LiF/PTCDI-C8 and LiF/pentacene were prepared and their morphology and molecular structure were characterized using X-ray reflectivity (XRR) technique. In order to study the effects of the films' structures and dielectric/organic interfacial properties on the device performance, OTFTs based on these bilayers were fabricated and characterized. It has been observed that PTCDI-C8 thin films have higher molecular packing in the LiF/PTCDI-C8 bilayer structure, which results in superior electrical characteristics for OTFTs based on this organic material. Devices with LiF/PTCDI-C8 bilayer exhibit about one order of magnitude higher output current (I_(ds)) at a constant drain-source voltage (V_(ds)) compared to the devices with LiF/pentacene bilayer. The observed differences in the electrical characteristics of these devices can be attributed to the effects of the dielectric/organic interface and the molecular structure of the organic layers.
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