A Semi-Localized Transport (SLoT) Model for Chemically Doped Semiconducting Polymers

Prof. Shannon Yee
Physics 120
Prof. Suchi Guha

Chemically doped semiconducting polymers exhibit electronic transport characteristics that range from localized (or hopping-like) transport to delocalized (or metal-like) transport.  While a multitude of electronic transport models have been proposed, none of them capture the full spectrum from localized to delocalized transport.[1]  Additionally, existing models do not quantitatively capture the dependency on charge carrier density (or carrier concentration or carrier ratio) that manifests through the measured temperature-dependent electrical conductivity and Seebeck coefficient.  Recently, we developed a semi-localized transport (SLoT) model, building upon past insight,[2] that can describe the full spectrum from localized to delocalized transport.[3]  This new model provides quantitative insight into charge carrier localization that is capable of more accurately describing electronic transport in a broad spectrum of organic electronic and thermoelectric semiconducting polymers.  This invited talk will discuss our recent publication[3] where I will first present motivation showing the previous short comings of our collective understanding with existing models.  Next, I will briefly discuss the development of the SLoT model in the context of the organic thermoelectric field.  I will then discuss the utility and prospects of deeper insight that the SLoT model affords.  Then I will validate the model using the prototypical P3HT polymer doped with FeCl3 and show its broad applicability in accurately describing other polymers/organic materials (namely, PBTTT, PA, PEDOT, SWCNT, and N2200) that were not previously well described by other models.  I will then extend this process to new polymers (namely PE2) and describe the deeper insight gained from this model.  I will then conclude my talk describing the relevant experimental measurements that research groups should undertake in characterization of their polymers to be able to use the SLoT model, in hopes of encouraging uniform material characterization internationally.  The future implications of the SLoT model in developing semiconducting polymers could be profound.  When coupled with chemical and structural characterization, the SLoT model connects the chemistry and structure to the macroscopic transport properties.  Once the SLoT model parameters are calculated, we can quantify fundamental limits to a polymer’s potential (e.g., ability to achieve high electrical conductivity or high Seebeck coefficient).  Ultimately, this allows us to accelerate the rational development of chemically doped organic electronics affording new functionality (e.g., thermal or electronic switching, thermoelectric cooling or power generation, etc.).