| NSF Org: |
DMR Division Of Materials Research |
| Recipient: |
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| Initial Amendment Date: | July 29, 2015 |
| Latest Amendment Date: | July 29, 2015 |
| Award Number: | 1533954 |
| Award Instrument: | Standard Grant |
| Program Manager: |
John Schlueter
jschluet@nsf.gov (703)292-7766 DMR Division Of Materials Research MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | August 15, 2015 |
| End Date: | December 31, 2019 (Estimated) |
| Total Intended Award Amount: | $359,531.00 |
| Total Awarded Amount to Date: | $359,531.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
1805 N BROAD ST PHILADELPHIA PA US 19122-6104 (215)707-7547 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
1901 N. 13th St. Philadelphia PA US 19122-6027 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | DMREF |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
ABSTRACT
NON-TECHNICAL SUMMARY
Organic semiconductors have many applications in portable, large-area or ubiquitous electronics. They also have great potential in bioelectronics as active materials in sensors or transducers. All such devices work by transporting charges; finding materials with large charge mobilities is therefore a major goal in the field of organic electronics. The search for high-mobility organic semiconductors, however, is still largely conducted with an Edisonian philosophy. The primary goal of the proposed activity is the development of a set of rational design principles for creating high-mobility conjugated homopolymers and copolymers which will impact all applications of organic semiconductors, from solar cells to light-emitting diodes and transistors. Insight derived from theory will be used to design and synthesize molecules that will be analyzed experimentally using X-ray diffraction for structural characterization and optical spectroscopy for measuring charge delocalization. These attributes will be correlated with the ability of the materials to carry current. The ultimate goal is to link specific features of the molecular structure and of the short-range arrangement of molecules within the assembly to carrier mobility. The methods developed, both theoretical and experimental, can potentially streamline the search for high mobility polymers and pave the way for the next generation of high-performance organic-based electronic devices.
TECHNICAL SUMMARY
Rational design of functional materials will be based on a theoretical model that accounts for charge transport, nuclear-electronic coupling, and various manifestations of diagonal and off-diagonal disorder within a two-dimensional lattice appropriate for mixed or segregated pi-stacks. Design principles derived from theory will be tested on several model Donor-Acceptor copolymers in which intrachain torsional disorder and/or HOMO energy alternation is carefully controlled. Structure/property relationships will be evaluated on high-performance copolymers based on the indacenodithiophene structural motif using acceptors with varying electron-withdrawing strengths. Microstructural characterization of thin polymer films will be accomplished using grazing incidence X-ray diffraction (GIXD), and charge delocalization will be probed using charge modulation spectroscopy (CMS) on oriented samples in order to obtain polarization resolution. The proposed activity will provide the organic electronics community with a method to experimentally and theoretically evaluate materials quickly for the design of high-performance organic semiconductors. It will also provide the first measurements of the coherence length of polarons in conjugated polymers using steady-state infra-red absorption spectroscopy. The coherence length will be linked to the design of new conjugated polymers and their short-range morphologies, thereby providing fundamental insights into what governs delocalization and trapping in conjugated polymer films.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Organic semiconductors such as conjugated polymers find many applications in portable electronics such as displays and sensors as well as in energy generation such as in solar cells as they promise to be cheap and have a low embodied energy. A major impediment to the economic success of these materials in the marketplace is their inferior ability to move electronic charges compared to conventional (inorganic) semiconducting materials. One major outcome of this work is to show how the assembly of semiconducting polymers at the molecular scale affects the charge mobility – which measures how rapidly the electronic charges can move in response to an electric field. For the first time we provide a quantitative measure of how delocalized or “spread-out” the electronic charges are both along a polymer chain as well as between neighboring polymer chains. The delocalization range is a special quantum mechanical property which indicates the length over which the charge behaves like a wave. We then used the delocalization metric to demonstrate that in order obtain high charge mobilities the electronic charges must be delocalized over several polymers within a crystalline region of a polymer film. Furthermore, we show that such crystalline regions must be interconnected by special polymer chains called tie chains for optimal mobilities. Finally, we explain why introducing charges chemically (“doping”) is less effective than introducing them with an electric field (“field-effect”) by showing that in the former case the charges become bound or “stuck” on small molecular segments near the oppositely-charged dopant ion. The three-way collaboration funded by this award was crucial in reaching these fundamental conclusions as very well-defined materials were needed to be synthesized ad hoc, in order for the measurements to be of sufficient quality to allow them to be interpreted by theory.
In terms of broader impacts, our results constitute a firm foundation upon which the rational design of new materials and of processing methods to achieve optimal microstructures can be built. Optimizing the ability of organic materials to transport charges is essential for them to effectively compete in the marketplace. Furthermore, doctoral students were trained in synthesis, materials characterization and theory in a field of growing employment opportunities.
Last Modified: 03/30/2020
Modified by: Francis C Spano
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