Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 28, Issue 41, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201804142
Keywords
carrier mobility; charge delocalization; charge transport; polarons; structure-property relationships
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Funding
- National Science Foundation [DMREF-1533987, 1533372]
- NSF [DMR1708317, DMR 1720256]
- State of Washington through the University of Washington Clean Energy Institute
- Washington Research Foundation
- Department of Energy Office of Basic Energy Sciences [DE-SC0016390]
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Charge transport in semiconducting polymers is inextricably linked to their microstructure, making the characterization of polymer morphology at all length-scales essential for understanding the factors that limit mobility in these materials. Indeed, charge transport depends both on the ability of polarons to delocalize at the approximately nanometer length-scale and navigate a complex energetic and morphological mesoscale landscape. While characterization of the mesoscale morphology of polymers is well-established, studies of the local chain packing and nanoscale disorder, which affect delocalization, can be significantly more difficult to carry out. Through infrared charge modulation spectroscopy and theoretical modeling, the effect of the local chain environment on polaron delocalization is directly measured and quantified. Using a series of polymers based on the model system, poly(3-hexylthiophene), the link between disorder and polaron localization is systematically explored. Polaron delocalization is correlated with known trends in mobility, revealing that while charge delocalization is always beneficial, the formation of tie-chains is necessary to reach the highest mobilities in semicrystalline polymers. The results provide direct evidence for the importance of both nanoscale (charge carrier delocalization) and mesoscale (tie-chains) orders, demonstrating the need to distinguish the key length-scale limiting charge transport in the design of new, high mobility polymers.
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