Date of Completion

7-31-2015

Embargo Period

1-27-2016

Major Advisor

Gregory Sotzing

Associate Advisor

Douglas Adamson

Associate Advisor

Jing Zhao

Field of Study

Chemistry

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Conjugated polymers (CPs), also known as conducting polymers are polymers consisting of alternating single/double bonds along the polymer backbone. They are known to be conductive upon doping. One important property of CPs is their ability to undergo reversible redox switch from a neutral (insulting) state to an oxidized (conducting) state upon potential application. Induced by electrical stimuli, accompanied with the change in electronic state of the material is usually a distinguishable change in the materials absorption characteristics within the visible region (400–800 nm) or near IR region, resulting in the material’s color change, known as “electrochromism”.

In order to have useful Electrochromic applications, conducting polymers should be built into electrochomic devices (ECDs). We have developed a novel processing technique of conjugated polymers for large area electrochromic device manufacturing. Compared with conventional device fabrication process, this novel approach, termed “in situ assembly”, eliminates the solution step, has resulted in less waste, versatility in device manufacturing, the ability for open atmosphere fabrication, and shorter device assembly time by direct conversion of monomers in a cross-linked solid polyelectrolyte matrix after device construction.

This dissertation is focused on conducting polymers and electrochromic devices (ECDs) assembled from “in situ” method and divided into two corresponding main parts. PART I (Chapter 3 and Chapter 5) is focused on the development of gel polymer electrolyte materials for supporting the maximum functioning of electrochromic devices prepared from the “in situ” approach. Chapter 3: a study on varying salts and their composition used in the gel polymer electrolyte for “in situ” assembly for electrochromic devices was carried out to explore their effects on various electrochromic performance parameters, such as color uniformity, photopic contrast, switching speed, and optical memory. It was found that the lithium salts yielded devices with the best color uniformity, photopic contrast as high as 48%, and switching response speeds as low as 1 s. Hermetically sealed electrochromic devices exhibited optical memory of 27 h for a 2% photopic transmittance loss under normal laboratory conditions. In Chapter 5, novel flexible gel polymeric electrolyte (GPE) materials were formulated and optimized. Electrolyte composition parameters were fully investigated and studied to maximize the performance of ECDs fabricated via the in situ method. An optimal polyelectrolyte demonstrated a high ionic conductivity of 1.36 × 10-3 S/cm and yielded ECDs with a photopic contrast as high as 53% with less than 6% photopic contrast loss after 2000 switching cycles. More importantly, a systematic study was carried out on the mechanical flexibility properties of the gel electrolytes side by side with an evaluation of commercially available indium doped tin oxide (ITO) coated polyethylene terephthalate (PET) substrates. Optimized GPEs were found to withstand a much larger bending extent, exceeding that of ITO coated PET, ensuring that ECDs will function still under extreme stresses even if the substrate becomes damaged. PART II (Chapter 4 and Chapter 6) is the discovery of optimal color tuning methods to achieve a desired electrochromic device color. In Chapter 4, demonstrates the ability to achieve neutral color ECDs by adding a commercially available yellow dye into the gel polymer electrolyte utilizing the “in situ” device fabrication approach. The conjugated dye was shown to not interfere with the electropolymerization of our chosen monomer 3,4-ethylenedioxythiophene (EDOT), allowing a combinatorial effect in the subtractive color spectrum. Optimized polymer and yellow dye absorption intensities yielded neutral grey color ECDs with 30% photopic contrast and switch speeds as low as 1 second on flexible PET substrates. In addition, this study opens up new directions to tune optical and colorimetric properties of other EC polymers in combination with the use of commercially available dyes for increased contrast. Chapter 6 introduces a method to neutral color-tune flexible electrochromic devices using the “in situ” approach, where three monomers (1,3-di-tert-butyl-3,4-propylenedioxythiophene, 2,2-dimethyl-3,4 propylenedioxythiophene, and thieno[3,4- b ]thio-phene) were used to form two distinct copolymers. The monomer ratios for the conjugated random copolymers were predetermined and optimized via theoretical calculations to provide the most desirable optical properties when combined within an electrochromic device. The demonstration of color tuning based on determining feed ratios using two distinct complimentary copolymer systems consisting of only 3 monomers in a single electrochromic layer solid state device achieved excellent neutrality (2%) to date. And of note, this most neutral colored electrochromic device in the literature also demonstrated a highest reported photopic contrast of a neutral colored electrochromic device ca. 38%.

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