Understanding the molecular doping process of semiconducting polymers through In-situ conductivity measurements and structural characterization

Polymers with conjugated semiconducting backbones show promise for use in organic electronics, such as thin film transistors, organic photovoltaics and the emerging technology of organic thermoelectrics. Molecular doping is a vital step in the controlling the charge transport of semiconducting polymers. Here, we report on how molecular doping affects the conductivity of polythiophene-based polymers over the course of vapor doping, and how different dopants (fluorinated TCNQs) with variable HOMO-LUMO overlap with our polymers affect the observed conductivity trends. Through in situ conductivity experiments, we show that for all three dopants tested, the conductivity follows a distinct profile that shows rapid increase of conductivity up until an optimal time, after which it falls and then equilibrates between 90% to 50% of the optimal conductivity. In conjunction with our in situ conductivity experiments, we report on scattering and spectroscopy experiments such as GIWAXS, UV-Vis, and EPR spectroscopy on polymer-dopant films at various time-points throughout the doping process. This study shows the potential of these methodologies for use on various polymer-dopant pairings to further advance our understanding of molecular doping dynamics.