Journal
ADVANCED FUNCTIONAL MATERIALS
Volume 24, Issue 28, Pages 4515-4521Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adfm.201304247
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Funding
- National Science Foundation [DMR 1205752]
- Stanford Graduate Fellowship
- National Science Foundation Graduate Research Fellowship
- Center for Advanced Molecular Photovoltaics - King Abdullah University of Science and Technology (KAUST) [KUS-C1-015-21]
- Direct For Mathematical & Physical Scien [1206296] Funding Source: National Science Foundation
- Division Of Materials Research [1206296] Funding Source: National Science Foundation
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In this work, crystallization kinetics and aggregate growth of poly(3-ethylhexylthiophene) (P3EHT) thin films are studied as a function of film thickness. X-ray diffraction and optical absorption show that individual aggregates and crystallites grow anisotropically and mostly along only two packing directions: the alkyl stacking and the polymer chain backbone direction. Further, it is also determined that crystallization kinetics is limited by the reorganization of polymer chains and depends strongly on the film thickness and average molecular weight. Time-dependent, field-effect hole mobilities in thin films reveal a percolation threshold for both low and high molecular weight P3EHT. Structural analysis reveals that charge percolation requires bridged aggregates separated by a distance of similar to 2-3 nm, which is on the order of the polymer persistence length. These results thus highlight the importance of tie molecules and inter-aggregate distance in supporting charge percolation in semiconducting polymer thin films. The study as a whole also demonstrates that P3EHT is an ideal model system for polythiophenes and should prove to be useful for future investigations into crystallization kinetics.
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