Organic semiconductors are a promising class of materials with the potential to revolutionize advanced electronic devices, from flexible displays to high-efficiency solar cells. Their widespread use is currently limited by atomic-level motions that, in many cases, reduce the effectiveness of the material. In this project, these motions – specifically those that occur at terahertz frequencies – will be investigated using a combined experimental and computational approach. The PI will investigate and quantify the precise dynamics that influence the performance of organic semiconducting materials with atomic-level precision. Through this research an unprecedented level of insight will be gained, which translates to the ability to rationally engineer new materials that suppress detrimental phenomena. This research is strongly connected to the training and education of young scientists, with trainees directly involved in the research from all career stages, from undergraduates to postgraduates. In addition, the PI will develop a university-level course that incorporates the results of this research in order to further enhance the training of young scientists. The trainees involved in the research, in conjunction with the PI, are also directly involved in efforts to communicate this cutting-edge research to the wider community. Through a collaboration with a local art museum, the PI is working to expand the reach of the developed methods to aid in the characterization, identification, and preservation of artwork in their collections. This is extended to K-12 education through a partnership with a local school district, where workshops and training opportunities are offered, providing a convergence of cutting-edge research with the development of the next generation of STEM professionals.
The role that low-frequency (terahertz) dynamics play in a wide-variety of bulk phenomena in organic semiconductors has been elucidated in recent years. Specifically, large-amplitude vibrational motions occurring at terahertz frequencies have been shown to be pivotal to rationalizing the charge-carrier dynamics of these materials. In many cases, detrimental electron-phonon coupling from a single-terahertz vibration is sufficient to significantly reduce charge-carrier mobility, a critical parameter for realizing advanced electronics. This research leverages experimental terahertz time-domain spectroscopy with quantum mechanical simulations to explore the crucial role that terahertz phonons play on the properties of organic semiconducting solids. This project involves the design and implementation of new experimental and theoretical methods – methods that are also applicable to solid-state materials in general. Specifically, optical pump-terahertz probe spectroscopy is used to directly sample both charge-carrier dynamics, as well as electron-phonon coupling, while anharmonic density functional theory simulations are performed to predict temperature- and pressure-dependent properties. The results of these experiments are used to rationally design new materials, using experimental organic synthetic methods as well as computational crystal structure design. This research also integrates multiple educational activities that are a benefit to a wide cross-section of society, including future STEM leaders and the non-scientific community. Through a collaboration with the Fleming Museum of Art, terahertz imaging methods are applied to reveal hidden features in artwork, such as a signature obscured by layers of paint. An exhibit based on this research is planned to be put on display at the museum, along with workshops for the general community and K-12 students. Additionally, a new course for advanced undergraduates and graduate students is being developed based on this project, which will translate to growing expertise in this important area of the materials sciences.
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.
