Injection, Transport, and Ionic Interactions of Carriers in Polyacetylene Ionomers as Probed by Near-Infrared Absorbance and Visible Photoresoponse
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While mixed ionic-electronic conductors (MIECs) show promise in a number of different device structures, their successful application has been inhibited by difficulties with characterization. The simultaneous influence of both ionic and electronic systems often foils attempts to quantify material parameters important for rational device design. In many cases, even general models of MIEC function can prove uncertain or controversial. This dissertation addresses the broader issue of ambiguity in MIEC characterization by exploring near-infrared absorbance as a method of gaining further insight into these systems. In combination with a traditional suite of techniques, this method enables determination of parameters not otherwise accessible. The determination of a concentration-dependant carrier mobility in an MIEC material will be demonstrated, and MIEC conduction in the unipolar regime will be broadly described as a system of electrochemically-supported charge injection. This model will be subsequently expanded to describe an unusual and previously unreported phenomenon of rectification when MIECs are interfaced with otherwise appropriate semiconducting contacts. A model labeled as extracting-electrode space-charge limited current will be described and experimentally demonstrated. Finally, the unique photovoltaic properties of an ionic heterojunction system comprising two MIECs will be examined. The results will be used to gain insight into the role of ionic asymmetry in the behavior of MIEC interfaces. This dissertation contains coauthored, previously published, and unpublished work.