Space-charge-limited conduction in ethyl-hexyl substituted polyfluorene

Ethyl-hexyl substituted polyfluorene (PF2/6) is a model blue-emitting polymeric system where the space-charge-limited conduction model within discrete single-level shallow traps can be applied to describe charge transport. Thermal cycling the PF2/6 film to a crystalline phase prevents creation of additional trap states, which is seen in the as-is polymer at higher voltages. These results shed new light on the mechanism of charge transport in polymers. Although PF2/6 has a high degree of interchain disorder, the as-is polymer shows regions of ordering that impacts charge transport through the polymer. Current-voltage characteristics as a function of the polymer thickness reveal the origin of the trap states.