UCLA

This thesis focuses on studying and controlling the structure of pristine and doped semiconducting polymers. Semiconducting polymers have many applications in flexible electronics due to their structural tunability, low cost and solution processability. Intrinsically, semiconducting polymers have poor conductivities due to a lack of mobile carriers. Charge transfer between a semiconducting polymer and a dopant molecule is necessary to introduce carriers into a polymer system. If an electron is fully transferred, commonly called “integer charge transfer (ICT)”, this will result in a polaron and a dopant anion. On the other hand, the electron charge could be shared between the polymer and a dopant molecule to form a “charge transfer complex (CTC)”. In the first part of the thesis, we explored factors that affect the charge transfer pathways in doped semiconducting polymers and were able to control the formation of CTCs. Semiconducting polymers are composed of both crystalline and amorphous parts. Compared to crystalline regions, amorphous polymer parts are disordered, thus the dopant anion is usually close to the polarons, resulting in poor carrier mobility due to Columb attraction between polarons and counterions. CTCs also tend to form in amorphous polymer regions compared to crystallites and result in less carriers due to the charge-sharing nature of CTC. In our second project, we explored ways to suppress the formation of both CTCs and localized carriers even in highly amorphous polymer films, using large boron cluster-based dopants. The electron density of these dopants is core-localized and is shielded from the holes on the polymer, resulting in increased crystallinity and higher film conductivities. In our third project, we further explored how polymer crystallite orientation influences the ease of doping and found that polymer regions with structures similar to the final doped structure could be doped more easily. In the last chapter, we designed amphiphilic semiconducting polyelectrolytes that form ordered cylindrical micelles in water. Our results demonstrate that we can achieve relatively precise control between electron donor and acceptor co-assemblies by varying the structural properties of component amphiphilic polymers and acceptors, which can provide guidelines for designing systems with controllable excited-state transfers.