Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Jianguo Mei

Committee Member 1

Chengde Mao

Committee Member 2

David R McMillin

Committee Member 3

Tong Ren

Abstract

Semiconducting polymers are considered as the materials for the next generation large-area and flexible electronics. In the past several decades, extensive effort has been to understand and improve the charge transport properties of semiconducting polymers. Chapter one is an introduction to organic semiconductors and complementary semiconducting polymer blends. Complementary semiconducting polymer blends is recently proposed and established by our research group. The complementary semiconducting polymer blends consist of a matrix polymer (main component, with intentionally introduced flexible conjugation break spacer along the polymer backbone) and a tie chain polymer (fully-conjugated polymer). Previous studies on these blends have shown that with 1 wt% of the tie chain polymer in the matrix polymer, charge carrier mobility becomes two orders of magnitude higher than the matrix polymer and lies in the same order of the tie chain polymer. The subsequent chapters describe the synthesis and characterizations of semiconducting polymers with different structural features. Chapter two details the influence of the length in the matrix polymer to the physical properties and charge transport of the matrix polymer and the complementary semiconducting polymer blends. The results reveal that with longer side chains, matrix polymers exhibit lower melting points, higher crystallinity and lower charge carrier mobilities. Profound odd-even effects are also observed in these properties. As for the complementary semiconducting polymer blends, charge carrier mobilities is less sensitive to the conjugation-break spacers. Chapter three presents a series of matrix polymers with different side chains and the physical properties and charge transport of these polymers and the complementary semiconducting polymer blends. The chapter describes that side chain has a significant influence on the physical properties of the polymers. Specifically, polymers with asymmetric side chains exhibit much lower melting points than the symmetric analogues. As for charge carrier mobilities, polymers with alkyl and siloxane-terminated side chains show similar properties, whereas the presence of oligoether side chain leads to a decrease for orders of magnitudes. Chapter four focus on the influence of the molecular weight of the tie chain polymer on the charge carrier mobilities of the complementary semiconducting polymer blends. The result shows that although for the tie chain polymer itself, molecular weights higher than a certain region leads to decrease in charge carrier mobilities, for the complementary semiconducting polymer blends tie chain polymer with higher molecular weight is in favor of charge transport.

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