Controlling the Morphology and Electronic Properties of Conjugated Polymer/Metal Interfaces

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This project addresses how molecular-level structure of polymer/electrode interfaces is related to optoelectronic device performance. When a metal is evaporated onto a conjugated polymer, car-bon-carbon bonds may be broken, metal-carbon bonds may be formed, and the polymer may be-come electrically doped. Additionally, the way charge is injected into polymer-based devices is determined by details of the chemistry at polymer/metal interfaces. The approach pursued takes advantage of surface-specific non-linear optical spectroscopies, second harmonic and sum fre-quency generation, to directly probe the chemical structure of conjugated polymer interfaces. Ini-tial experiments focus on polymer/vacuum interfaces, relating non-linear optical signals with morphological information from microscopic (AFM) studies. Additional experiments will ex-plore the existence of metal-carbon bonds and the extent of doping of the polymer at poly-mer/metal interfaces. Additionally, interfacial carrier dynamics will be probed in operating de-vices, allowing device performance to be correlated with specific changes in polymer/metal inter-facial structure. The overall goal is to relate interfacial properties and morphology with device performance, so that the interfaces can be optimized for desired applications. %%% The project addresses fundamental research issues associated with electronic/photonic materials having technological relevance. The broader impacts of this proposal are several-fold. The pro-posed experiments will educate students at the undergraduate, graduate and postdoctoral levels in the subject areas of lasers, optics, advanced spectroscopies, nanometer-scale structural measure-ments, semiconductor physics, and optoelectronic device fabrication. Moreover, these educa-tional opportunities will be provided to students traditionally under-represented in the physical sciences. Because metal electrodes are necessary for the operation of any type of polymer-based device, the methods and measurements developed in this project will enhance areas of research outside the immediate focus of the project. ***