Structural origin of gap states in semicrystalline polymers and the implications for charge transport

Abstract
We quantify the degree of paracrystalline disorder in the π-π stacking direction of crystallites of a high performing semicrystalline semiconducting polymer with advanced x-ray line-shape analysis. Using density functional theory calculations to provide input to a simple tight-binding model, we obtain the density of states of a system of π-π stacked polymer chains with increasing amounts of paracrystalline disorder. We find that, for an aligned film of PBTTT, the paracrystalline disorder is 7.3%. This type of disorder induces a tail of trap states with a breadth of ∼100 meV as determined through calculation. This finding agrees with previous device modeling and provides physical justification for the mobility edge model. © 2011 American Physical Society.

Citation
Rivnay J, Noriega R, Northrup JE, Kline RJ, Toney MF, et al. (2011) Structural origin of gap states in semicrystalline polymers and the implications for charge transport. Physical Review B 83. Available: http://dx.doi.org/10.1103/PhysRevB.83.121306.

Acknowledgements
Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University on behalf of the US Department of Energy, Office of Basic Energy Sciences. A. S. and J. R. gratefully acknowledge financial support from the National Science Foundation. This publication was partially based on work supported by the Center for Advanced Molecular Photovoltaics (Award No. KUS-C1-015-21), made by King Abdullah University of Science and Technology (KAUST). Work at the Palo Alto Research Center (PARC) was supported by AFOSR Grant No. FA9550-09-1-0436. The authors thank Drs. Iain McCulloch and Martin Heeney (Imperial College, UK) for providing the PBTTT samples.

Publisher
American Physical Society (APS)

Journal
Physical Review B

DOI
10.1103/PhysRevB.83.121306

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