Electrochromic devices: From windows to fabric

Date of Completion

January 2010

Keywords

Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

This dissertation focuses on electrochromic and conducting polymers and devices thereof. Chapter 3: An ion storage layer, poly(thieno[3,4- b]thiophene), was used in the assembly of electrochromic devices (ECDs). Its high-doping level and low-absorption in the visible region in both its oxidized and neutral states makes it an ideal candidate for use as an ion shuttling layer in ECDs. This layer did not distort ECD color, nor does it have a yellowed tint to it (as some previous materials) that may distort vision over time. The characterization of a novel substituted 3,4-propylenedioxythiophene, 1,3-dimethyl (1,3-DM-ProDOT), is also presented. Chapter 4: The precursor polymer method, which imparts solubility and processability to electrochromic precursors, allowed for the preparation of electrochromics inside assembled solid-state devices. The same polymeric material can be made through in situ conversion (oxidation inside an assembled device) as via solution methods (ex situ conversion via electrochemical or chemical oxidation), saving a step in device preparation. Clean substrates were not needed for this method, removing another step in device production. A study of the effects of precursor film thickness, gel electrolyte composition (including the use of ionic liquids), and comparison to traditionally assembled (ex situ) devices is illustrated therein. These precursor polymers have also been ink-jetted, expanding their utility to a large variety of complex electronics. Further, the use of these materials to prepare easily-assembled electrochromic sunglasses is discussed. The in situ method was also extended to using monomers inside of the electrolyte and electropolymerization thereof. This method offers a simpler still method for ECD assembly. This system was studied with respect to higher contrasts and unique patterning abilities, as well as for a variety of chromophores. Chapter 5: A new side-chain based precursor polymer was developed using a single pendant heterocycle. This represents a simpler synthetic route to soluble side-chain precursor polymers. As a comparison, a trimeric unit composed of this single heterocycle attached to a central thiophene unit is also incorporated into the side chain precursor polymer method. Films of both are compared with respect to conversion conditions, electrochromic properties, and ease of synthetic procedure. Further, electrospun nanofibers of the single-heterocycle pendant material were prepared and studied, showing higher contrasts. Chapter 6: Aqueous conversion of a precursor polymer to an electrochromic was accomplished and investigated towards greener processing for conjugated polymers. It is shown that the material which is obtained by conversion in aqueous electrolyte is identical, or nearly identical, to that prepared using conventional, organic electrolytes (based upon spectral and colorimetric data). Both side-chain and main-chain precursor polymers are converted via this method, which involved pre-loading of a salt into the prepared film prior to oxidative conversion to the conjugated material. Chapter 7: Fabric-based electrochromic devices were developed, using a new device design. These devices do not require the use of a popular electrode material, indium-doped tin oxide (ITO), in their construction. Reflective ECDs were built with these fabrics, representing a significant step towards the realization of wearable displays. Stainless steel woven meshes are used, as well as PEDOT-PSS loaded spandex. Several device architectures have been described, allowing for two-sided displays to be envisioned. Further, the use of carbon black loaded poly(caprolactone) (CB-PCL) films as a counter electrode for these spandex devices was also achieved, showing the versatility of electrode systems that could be used with this system. A study of the effects of underlying substrate color on the electrochromic was also undertaken. Chapter 8: A new template, sulfonated poly(amic acid), was used to prepare PEDOT dispersions (PEDOT-SPAA). Previous work with a colleague has shown that DNA can also template polymerize EDOT to PEDOT, resulting in biocompatible and bioactive films. This template system was chosen to enhance the overall thermal stability of the conducting polymer. Conversion of the SPAA template to the imide form, SPI, resulted in high thermal stability as compared to conventionally prepared and commercially available PEDOT-PSS. Enhanced conductivity (10-fold enhancement) has been observed, without doping, upon conversion to the imide (PEDOT-SPI), resulting from the morphological changes that result from this conversion. Further expansion of this work includes the use of a different conducting polymer (poly(aniline) [PANi] and poly(pyrrole) [PPy]), a different template material (sulfonated Kapton© type amides and imides), as well as an exploration of the potential use of a variety of thermally stable dopants as compared to traditional systems used with PEDOT-PSS. ^

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