Understanding Structure-Function Relationships in Semiconducting Polymer Morphology
- Author(s): Winchell, Katharine Adele
- Advisor(s): Tolbert, Sarah H
- et al.
Semiconducting polymers are a promising class of materials for many organic electronic applications because of their structural tunability, low cost, and solution processability, which allows for easy scale-up. However, semiconducting polymers have intrinsically poor conductivity which limits their performance in all device applications. Polymer conductivity can be improved either by adding mobile carriers to the system or by manipulating the system to make the polymer chains more ordered on a local and global scale. This thesis studies both of these methods with a goal of improving polymer conductivity, while simultaneously seeking to understand how changes in morphology affect both local and global polymer properties. We used a variety of X-ray and neutron scattering techniques to characterize polymer structure, coupled with electronic and spectroscopic experiments to gain a full picture of polymer structure-function relationship.
The first half of this thesis studies the structural changes that result from introducing a molecular dopant and additional charge carriers into the polymer network, and how those change control the resulting electronic and optical properties. We start by studying a novel class of large, redox-tunable dodecaborane-based dopants. From these studies we are able to determine how redox potential controls both dopant infiltration into polymer films and the resulting film structure, providing insight into the relationship between structure and conductivity for doped conjugated polymer systems. Using traditional small-molecule dopants, we also studied various doping methods to assess scalability and application to thick polymer films.
The second half of this thesis presents studies on various methods to manipulate the local morphology of polymer chains to increase their overall order. We first used an aqueous amphiphilic self-assembly system where we developed structural design rules for order assembly and demonstrate that they can be used to create polymer system that show straightened chains when self-assembled. Next, we explored a set of block-copolymers whose co-crystallization properties could be changed using the polymer molecular weight; here we show that crystallization behavior directly affects conductivity. Lastly, we studied a host-guest system of polymers aligned in straight silica mesoporous, with a goal of using confinement to understand the interplay between polymer microstructure and aggregation.