Structural origin of gap states in semicrystalline polymers and the implications for charge transport
We quantify the degree of disorder in the p-p stacking direction of crystallites of a high performing semicrystalline semiconducting polymer. Using first principles calculations, we obtain the density of states of a system of p-p 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 induces a tail of trap states with a breadth of ~100 meV as determined through calculation. This finding agrees with previous device modeling and spectroscopic evidence, and provides physical justification for the mobility edge model.
J. Rivnay, R. Noriega, J. E. Northrup, M. F. Toney, R. J. Kline, and A. Salleo. Structural origin of gap states in semicrystalline polymers and the implications for charge transport. Physical Review B. 2011 March 15; B 83 (12): 121306.