Measuring Microscopic Charge Transfer Rates in Heterogeneous Thin Films

With support from the Chemical Structure and Dynamics (CSD) program in the Division of Chemistry, Professor Aaron Massari at the University of Minnesota-Twin Cities is investigating the roles of molecular interactions in the charge transport characteristics of thin films for the development of efficient molecular electronic materials. Many promising thin film systems are highly heterogeneous with transport characteristics that vary wildly with position and length. Prof. Massari and his students will prepare polycrystalline and molecular thin films with systematically controlled structures and use two-dimensional IR (2D-IR) spectroscopy to measure their charge transport characteristics. Their studies will advance the understanding of how molecular structure and interactions in a thin film control the movement of electrical charges. This work will inform the design of electrical materials that benefit society as a whole by leading to devices that are less toxic and require less energy to produce. Prof. Massari is the Director of the Energy and U Show; a high-octane stage show that brings science to over 10,000 3rd–6th graders to the U of MN campus each year to learn about the First Law of Thermodynamics and college education. This work will leverage the nonlinear nature of 2D-IR spectroscopy to extract charge transport dynamics from the naturally heterogeneous environments of thin films while electrically mobilizing charges with an AC voltage. The emphasis is on ground state electron transport though doped organic films, and the studies will specifically address the role of polymorphism, donor-acceptor spacing, degree of charge transfer, and covalent attachment of dopants in facilitating charge transport. Experimental studies to directly support (or disprove) the role of these structural parameters in molecular electronic films will advance the level of understanding needed to modify current models of charge conduction. The outcomes of these experiments will eliminate assumptions about the molecular structures through which charges are transported efficiently and could be used to make existing models more accurate and predictive. This will advance the level of understanding in the area of molecular design and synthesis by prescribing the features that need to be built into next generation molecules to impart efficient thin film performance. The interdisciplinary nature of these projects will support a training environment for undergraduate and graduate students that produces next-generation scientists who are skilled in benchtop chemistry, but also electrical, microscopic, and spectroscopic characterization techniques. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.