Morphology and Electronic Properties of Semiconducting Polymer and Branched Polyethylene Blends.

A new strategy for influencing the solid-state morphology of conjugated polymers was developed through physical blending with a low molecular weight branched polyethylene. This non-toxic and low boiling point additive was blended with a high charge mobility DPP-based conjugated polymer and a detailed investigation of the new blended materials was performed by various characterization tools, including X-ray diffraction, UV-Vis spectroscopy and atomic force microscopy. Interestingly, the branched additive was shown to reduce the crystallinity of the conjugated polymer, while promoting aggregation and phase separation in the solid-state. Upon thermal removal of the olefinic additive, the thin films maintained a lower crystallinity and aggregated morphology in comparison to a non-blended polymer. The semiconducting performance of the new branched polyethylene/conjugated polymer blends was also investigated in organic field-effect transistors, which showed a stable charge mobility around 0.3 cm2V-1s-1 without thermal annealing, independent of the blending ratio. Furthermore, by using the new polyethylene-based additive, the concentration of conjugated polymer required for the fabrication of organic field-effect transistor devices was reduced down to 0.05 wt.%, without affecting charge transport, which represents a significant improvement compared to usual concentrations used for solution deposition. Our results demonstrate that the physical blending of conjugated polymer with non-toxic, low-molecular weight branched polyethylene is a promising strategy for the modification and fine-tuning of the solid-state morphology of conjugated polymers without sacrificing their charge transport properties, thus creating new opportunities for the large-scale processing of organic semiconductors.