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

Abstract

We quantify the degree of disorder in the – 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 – 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.