cfaed Seminar Series

Abstract

The recent development of semicrystalline polymer semiconductors with field-effect mobilities comparable to, and in some cases, exceeding those of amorphous silicon has exposed the limitations of a description of charge transport using disorder-based charge transport models which were developed originally for more disordered, lower mobility materials.
I will present our recent results on the electrical characterisation of a range of semicrystalline polymers for which we observe a charge density dependent mobility correlated to the increase of crystallite size in the polymer film. Combining the results of structural, spectroscopic, electric and thermoelectric measurements we provide conclusive evidence that charge transport in this class of materials is incompatible with a description based on energetic disorder effects. [1]
We show direct experimental evidence for narrow band, disorder free conduction at the charge densities typically observed in thin film transistors. To explain these results, we propose a model for charge transport that explicitly accounts for the presence of interdispersed crystalline and amorphous regions within the polymer film and for the Coulomb interaction between charge carriers accumulated within the same crystallite. This approach captures all the unique features observed experimentally, and provides a rationale for further improvement of both electric and thermoelectric performance of this class of materials.

[1] Di Pietro, R. et al. (2016), Coulomb Enhanced Charge Transport in Semicrystalline Polymer Semiconductors. Adv. Funct. Mater., 26, 8011.