Organic Semiconductor Devices: Contacts, Transport and the Nanoscale Limit

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The objective of this research is to understand the processes that govern the electronic properties of field-effect transistors with active regions made from organic semiconducting polymers. Of particular interest are: the injection of charge from metal electrodes into the polymer; the processes that limit the transport of charge within the polymer; and the effect of nanoscale structure on both. The approach uses three types of experiments: electronic measurements in transistors fabricated on the nanoscale; measurements of terahertz radiation emitted by the polymer as a means of inferring nanoscale charge dynamics in the bulk; and scanning tunneling microscopy techniques for spatially resolved determination of carrier density and band energetics.The intellectual merit of this work is that this research addresses several crucial unanswered questions of both fundamental interest (e.g. What is the ultimate limiting factor in charge transport through organic semiconductors? What happens at the metal-organic interface in terms of charge transfer and band bending?) and practical import (e.g. How can organic field-effect transistor device performance be optimized?). The broader impacts include research training and education of the technically literate workforce, and strong relevance to burgeoning technologies, such as flexible displays, printable electronics, organic light emitting diodes, and organic photovoltaics. Many of the same device physics issues addressed by this proposal are central to optimizing device designs in these technologies.