Connecting Junction Molecular Orientation to Excited State Structure and Dynamics in Organic Devices

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Printable electronic devices based on flexible organic-based materials have the potential to revolutionize how we renewably harvest and store energy. The arrangement of plastic molecules at interfaces between layers can determine whether the device performs well. However, there is currently limited knowledge of how such arrangements govern device performance. In this project, solar cells and light emitters printed from plastic inks are studied. These devices have important interfaces where power is generated and light is emitted. This project involves varying the arrangement of the molecules at these interfaces, monitored by powerful X-ray techniques. Correspondingly, power- and light-generating processes are measured and related to the arrangement of the molecules. The result will be a new capability to tailor molecule arrangements at interfaces to maximize device performance. Such a capability will enable flexible and printable technologies to dramatically reduce the cost of energy. Students involved in this project will take part in the Science Ambassadors Program by developing a plastic solar cell lab for high school students. This activity will demonstrate both the fundamental science and the potential of these technologies. The interdisciplinary and collaborative nature of the project will provide the students with expertise to communicate diverse viewpoints that will be required of the next generation of scientists.Optoelectronic properties in printable organic devices could be tailored for revolutionary applications through simple processing techniques that engineer interfacial structures, but there is a gap in knowledge to realize this goal. This gap is due to the difficulty in quantitatively resolving buried organic interfacial nanostructure and directly correlating this to fundamental device processes. In the proposed work, a suite of recently developed resonant X-ray nanoprobes will be used to quantify molecular orientation, aggregation, and mixing local to buried organic interfaces. These measurements will be combined with advanced studies of excited state structure and dynamics on the exact same device - eliminating uncertainties related to sample variability. The objective is to define quantitative relationships on how molecular ordering at buried organic junctions controls excited state dynamics connected to performance. It will be accomplished by systematically investigating all structural cases in planar junctions and extending this information to printed 3D heterojunctions. Our aim is not only to establish the general concepts, but to define the functional form of these relationships to enable designed properties in high-performing organic devices.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.