Book Description
Organic semiconductors are emerging as promising semiconductor materials for a wide range of electronic and electrochemical device applications including displays, electronics, solar cells, chemical sensors, and energy storage. Recent advances in molecular structure-property relationships and backbone and side chain engineering have enabled significant progress in improving their charge transport properties and carrier mobilities, which are now competitive with amorphous silicon. Moreover, over the past few years, a series of conjugated polymers with polar side chains have been developed to operate as mixed ionic/electronic conductors in aqueous media. Despite these advances, an understanding of the multiscale mechanism for ionic and electronic charge transport remains elusive, limiting further progress in materials development. Charge transport requires continuous coupling across all length scales (i.e., atomic to mesoscale). Understanding the local environments where ionic and electronic charges reside in a semiconducting polymer and the energetic landscape for charge transport are key questions to address in the search for designing better materials. The focus of this dissertation has been on attempting to improve our understanding of the relationship between structure and its impact on macroscopic properties. In this dissertation, I present several methods to characterize the structure of semiconducting polymers and discuss the role of structure on optoelectronic and electrochemical properties. In the first part of this dissertation, I present a series of methods to extract and measure the nanoscale and mesoscale order of semiconducting polymers using low-dose, high-resolution transmission electron microscopy images and data analytics. These results showcase the applicability of developing novel methods to characterize the rich, complex mesoscale structure of conjugated polymers with unprecedented detail. In the second part of this dissertation, I combine a series of electrochemical and structural characterization techniques to study polymer volumetric charging in a series of aqueous electrolytes. These novel semiconducting polymers have been specifically designed for electrochemical device applications that leverage ionic/electronic charge transport. This work elucidates complex polymer- and electrolyte- dependent structure-property relationships, which will help further developments on the rational design and understanding of this new family of materials. Overall, these studies suggest design principles to continue to advance the field of organic electronics.