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

TL;DR

This study investigates how structural disorder in semicrystalline polymers affects electronic trap states and charge transport, combining advanced X-ray analysis and first-principles calculations to connect microscopic disorder with device performance.

Contribution

It quantifies the disorder in semicrystalline polymers and links it to the formation of trap states, providing physical insight into charge transport mechanisms.

Findings

Paracrystalline disorder in PBTTT is 7.3%.

Disorder induces trap states with ~100 meV breadth.

Results support the mobility edge model for charge transport.

Abstract

We quantify the degree of disorder in the {\pi}-{\pi} stacking direction of crystallites of a high performing semicrystalline semiconducting polymer with advanced X-ray lineshape analysis. Using first principles calculations, we obtain the density of states of a system of {\pi}-{\pi} 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.