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Author

Jack LyFollow

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2019

Month Degree Awarded

February

First Advisor

Alejandro Briseno

Subject Categories

Polymer and Organic Materials | Polymer Science | Semiconductor and Optical Materials

Abstract

Realizing organic based active materials for electronic devices, such as thin film transistors and photovoltaics, has been long sought after. Advancement in the field driven by chemists, engineers, and physicists alike have bolstered organic based semiconductor performance levels to rival those of traditional inorganic amorphous silicon-based devices. Within the field of organic semiconductors (OSC), two categories of active materials may be generalized: (1) polymer and (2) small molecule semiconductors. Each class of OSC inherently have their own advantages and disadvantages. Polymer semiconductors (PSC) allow a wide range in tunability via choice monomers and side chain engineering to illicit desirable energy levels and morphological arrangements in the thin film. However, due its polymeric nature, long range crystallinity is limited. Thus, its performance is heavily hindered compared to the much more crystalline small molecule adducts. Though small molecule semiconductors do indeed achieve high performance in the device, design rules for realizing such performance benchmarks render this class of materials to be susceptible to degradation in ambient conditions, namely, via photo-oxidation vii In this dissertation, I address the issues of creating high performing polymer semiconductors in a thin film transistor device via tuning dihedral angles of the conjugated core. A bottom up synthetic approach utilizing planarizing torsion angle inducing moieties is exampled here between acceptor-donor and acceptor-acceptor designs. These findings may be further extended in realizing future high performing PSC. Regarding conjugated small molecules, I report the impact of employing a combination of different aryl and ethynyl substituents in tetra-substituted tetracenes upon photo-oxidative stability and the cycloreversion of oxidized chromophores to regenerate the parent molecule. Synthesis of target molecules presented in this dissertation is reviewed and presented. Techniques to gauge optoelectronic properties of formed OSC includes a combination of cyclic voltammetry, ultra-violet visible spectroscopy, ultra-violet photon electron spectroscopy, and time resolved spectral techniques. Collaborative efforts for forming functional devices and investigate underlying fundamental physics of device properties and photo-physics are also presented in this dissertation. Lessons learned from this work will help guide the design of future OSC for effective performance benchmarks and stability.

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