Semiconducting polymers have many advantages that make them applicable for organic electronics including low cost and ease of processing. However, they have intrinsically low conductivity because of a lack of mobile carriers. Extensive studies have been done on molecular doping of polymers with F<sub>4</sub>TCNQ, a small molecule with a low-lying LUMO that makes it capable of removing an electron from the polymer HOMO, creating a stable polaron positive charge. We have expanded this concept of molecular doping to a set of redox-tuneable dodecaborane (DDB) clusters. Using this new class of dopants and sequential processing, in which the dopant is deposited on top of a pre-cast polymer film, we have achieved very high P3HT conductivity, up to 10 S/cm. We have done extensive characterization both on the structure of the polymer and its conductivity with a variety of DBB dopants to create a full picture of the structure-conductivity relationship. We have used AC Hall effect to measure mobility and carrier concentrations, X-Ray diffraction to understand the morphological effects on conductivity and XPS to investigate the driving force for infiltration of such large dopants into the films. We have found that the structure of the DDB dopants is crucial to the high conductivity and mobility as compared to other dopants. The DBB anion has the negative charge localized on the core which causes it to be spatially separated from the positive carrier and thus more mobile. Further, structural studies have shown that the large DDB dopants are unable to enter the polymer crystallite which further separates the charges. Lastly, because the redox potential of the DDB dopant can be tuned by slight changes in the side chains, the structural advantages of this type of dopant can be maintained while making it applicable for a wide variety of organic electronic applications.

Understanding the structure-conductivity relationship of P3HT doped with redox-tuneable dodecaborane clusters

2019 Fall National Meeting

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