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CPOS Seminar: Structure, Thermodynamic, and Thermomechanical Characteristics of Semiconducting Polymers: Nomenclature, Property Conundrums, and Applications

Date and Time
Location
Elings 1601 (in-person only)
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Speaker: Distinguished Professor Harald W. Ade - Department of Physics and Organic and Carbon Electronics Laboratories (ORaCEL),  North Carolina State University, Raleigh, NCBiomolecular Science and Engineering
 
Bio: A gradute of Stony Brook University, H. Ade has been a faculty member at NCSU since Nov. 1992, rising through the ranks to Full Professor by 2001, and been named Distinguished Professor of Physics in 2014 and Goodnight Innovation Distinguished Professor in 2017. He has had an active and continually funded research program  and served as Director of Graduate Program in Physics from 2006-2013. Recognitions include R&D100 Award, NSF Young Investigator Award, APS Fellow, AAAS Fellow, Alumni Outstanding Research Award (twice, NCSU), Holladay Medal (NCSU), K. F. J. Heinrich Award, and Shirley Price for Outstanding Science and Halbach Award of Innovative Instrumentation (both at the Advanced Light Source). He is a Clarivate Analytics Highly Cited Researcher in the field of Materials Science since 2017, based in large part of his developedment of soft-ray resonant scattering methods and it use in organic electronics. Some of his external engagements include serving on the Scientific Advisory Committee of the Advanced Light Source (2011- 2019) and the BESSY-II Synchrotron Facility in Berlin, Germany (2006-2009), as well as the Scientific Advisory Council of the Helmholz Zentrum Berlin, Germany (2009 – 2012). He has conceived and coordinates interdisciplinary efforts at NCSU across the Carbon and Organic Electronics Laboratories (ORaCEL) and the Carbon Electroncs Cluster as part of the NCSU Chancellor Faculty Excellene Program. He is Chair of the 15th International Symposium on Functional π-electron Systems (Fπ -15)
 

Abstract: Organic semi-conducting polymer thin films are used in many organic electronic devices and have shown promising results in applications ranging from organic light emitting diodes to solar cells and biosensors.  The molecular packing of the polymers controls a number of optical and electronic properties and the thermal and thermomechanical properties are critical for devices stability in blends, processing strategies, and mechanical failure modes. Due to the molecular design, semi-conducing polymers exhibit a continuing range of paracrystalline disorder, yet at the same time, they do not behave like classic paracrystalline materials. In fact, the classic structure and property paradigms and associated nomenclature don’t seem to apply. Classic material design labels such as random coil, rigid rod, hairy rod and bottlebrush seem to be delimiting structural characteristics, with semi-conducing polymers occupying the concept and parameter space in-between these limits, yet with characteristics that appear to be not just linear combination of the characteristics found in the classical limits. We review the current understanding and the various conundrums. For example, paracrystallites in a semi-conducting thin film are usually assumed to have a certain size and shape in three dimensions, which then can have a preferred edge-on or face-on orientation relative to the substrate with a random orientation in-plane. X-ray analysis indicates though that most materials in their use-conditions exhibit only two-dimensional paracrystalline platelet ordering and might often resemble a layered glass. Thermomechanical characterization frequently indicate multiple relaxation transitions without the presence of a clear glass transition, yet a high temperature liquid-crystalline-like phase. Furthermore, the phase diagrams of semi-conducting polymers with ‘small molecule’ acceptors such as fullerenes or modern non-fullerene acceptors frequently exhibit reentrant phase boundaries that reflect upper and lower-critical solution temperature characteristics. The totality of information suggests that a new reference frame if not new paradigm and associated nomenclature is required to facilitate understanding and communication about the order, molecular packing, texture, thermomechanical properties, and structure-properties relations in semi-conducting polymers. In addition to delineating polymer science, we will provide a number of examples how these concepts matter in organic solar cells and impact stability and mechanical robustness.