Carrier hopping transport in semi-crystalline isotactic polypropylene thin films: A revisit to the overestimated hopping distance

Carrier transport and its dependence on morphology are key issues in semi-crystalline polymers. Although the hopping mechanism is widely accepted, the obtained hopping distance (λ) of isotactic polypropylene (iPP) is orders larger than the theoretical value, rendering the whole process ambiguous. In the study, with annealing at 150 °C for various durations, the morphology of iPP thin films such as grain structure, grain size and its distribution, and surface roughness is manipulated effectively, which has a direct influence on the carrier transport process. It is concluded that the intrinsic λ is about 0.1–0.2 nm, consistent exactly with the theoretical one. The dependence of λ and other microscopic parameters on temperature is well explained in terms of their morphological characteristics. For the optimal morphology, it exhibits not only lowest conductivity, but also good thermal stability. The present study clarifies the uncertainties of λ and correlates the morphology with carrier transport behaviour.