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Date of Award

Spring 2012

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

Supervisor

Shiping Zhu

Co-Supervisor

Yiliang Wu

Language

English

Committee Member

Carlos Filipe

Abstract

Organic thin film transistors (OTFTs) have attracted great attention in the last couple of decades due to their potential of cost reductions in manufacturing low-end electronic devices through solution processes. Currently, one of the major challenges facing the field of OTFTs is lack of high performance functional organic materials including both organic semiconductors and gate dielectrics for effective device integrations by solution deposition technologies. This thesis focuses on material designs, interfacial compatibilities, and device integrations for high performance OTFTs.

Research progresses in the following areas are presented in this thesis. First, novel liquid-crystalline organic semiconductors, 2,5‟-bis-[2-(4-pentylphenyl)vinyl]-thieno(3,2-

b) thiophene and 2,5‟-bis-[2-(4-pentylphenyl)vinyl]-(2,2‟)bithiophene for OTFT applications were developed. Mobilities of the OTFTs fabricated from these semiconductors reached 0.15 cm2/V.s with high environmental stability. Such high performance is attributed to their ability to form highly ordered molecular structures. Second, a simple effective approach was developed for tuning solubility of a high mobility polythiophene system through engineering its molecular structure. OTFTs fabricated with the newly developed copolythiophenes from an environmentally benign non-chlorinated solvent showed excellent performance with mobility up to 0.18 cm2/V.s. Third, an effective approach to a solution processed gate dielectric Ph.D. Thesis – P. Liu, McMaster University, Chemical Engineering iv

design was developed for all solution-processed flexible OTFTs. This was achieved through a dual-layer dielectric structure design comprised of a bottom layer with a UV-crosslinked poly(4-vinyl phenol-co-methyl methacrylate), (PVP-PMMA), and a top layer with a thermally crosslinked polysiloxane. This solution-processed dual-layer dielectric structure enabled all solution-processed high performance flexible OTFTs. Finally, flexible OTFTs were successfully integrated on plastic substrates (PET) from non-chlorinated solvents by using the copolythiophenes and the dual-layer dielectric. The integrated flexible devices showed good OTFT characteristics with mobility up to about 0.1 cm2/V.s.,

well defined linear and saturated regions, and a close to zero turn-on voltage.

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