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Quantifying Charge Transport in Chemically Doped Semiconducting Polymers

Authors
  • Gregory, Shawn A.
Publication Date
Apr 27, 2022
Source
Scholarly Materials And Research @ Georgia Tech
Keywords
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Abstract

Semiconducting polymers are a class of materials that engenders the solution processibility, mechanical compliancy, and biocompatibility of archetypal polymeric materials with the charge transport properties, optical properties, and device physics of archetypal inorganic semiconductors. Oftentimes, pristine semiconducting polymers are electrically insulative (σ<〖~10〗^(-4) S cm-1) with comparatively few mobile charge carriers with low mobilities. The charge carrier density and mobility can be increased via chemical doping, and chemical doping oftentimes involves adding or removing charge carriers from the pristine polymer via a redox chemical reaction. Ultimately, the resulting optical and electronic properties of chemically doped semiconducting polymers is a convoluted function of multiple parameters, including polymer chemistry, dopant chemistry, and processing techniques. While this convolution enables a nearly infinite number of permutations, each of which can be designed for a specific application, this convolution obfuscates the establishment of charge transport models, and fundamental process-structure-property relationships. In this thesis, I developed and compiled experimental methods, which are used to create and substantiate novel charge transport models, which are then used to contextualize the charge transport properties of chemically doped semiconducting polymers. This thesis begins by reviewing the electronic structure of materials, solid-state charge transport physics, and state of the art literature in organic electronics and thermoelectrics. Afterwards, a novel charge transport model (semi-localized transport, SLoT) is derived and applied to literature studies. The utility of the SLoT model is its ability to quantify both localized (hopping-like) and delocalized (metal-like) contributions to the observable transport properties and quantify key transport parameters such as the localization energy in the dilute doping limit, the carrier density need for delocalized transport, and the maximum hypothetical electrical conductivity. The SLoT model is then used to contextualize the transport properties in several chemically doped semiconducting polymer systems, that have systematic changes to the polymer chemistry, dopant chemistry, and doping level. Although the SLoT model captures the transport properties of several systems, it has shortcomings with electro-thermal transport modeling, so one chapter is devoted to developing models that capture this phenomenon. This work is concluded by detailing future experimental methods, transport models, and material systems that ought to be explored for the rational advancement of organic electronics and thermoelectrics. / Ph.D.

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