Fabrication and Characterization of Layer by Layer Assembled Single and Dual-Electrochrome Electrochromic Devices

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Virginia Tech

This thesis presents applications of the layer-by-layer (LbL) assembly technique in fabrication of thin films with a primary focus on design and development of electrochromic devices. The optical properties of electrochromic materials change as they alter between redox states. The morphology and properties of LbL-assembled thin films can be modified by varying several processing factors such as dipping duration, ion type, ion concentration, pH, molecular weight, and ionic strength. In the present work, several factors of LbL assembly process were manipulated to tailor electrochromic thin films of desired attributes.

An electrochromic device (ECD) with fast optical switching speed was designed and constructed based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). This device exhibited optical switching speeds of 31 and 6 ms for coloration and decoloration respectively, on a 60 mm2 area.

Poly(aniline 2-sulfonic acid) (PASA) is a relatively new ionic polymer, and its electrochromic properties have not been previously investigated in much detail. PASA thin film showed several redox states corresponding to color changes from dark blue to gray as it passed different redox states.

One particularly interesting and promising design for ECDs is dual electrochrome. Dual electrochrome ECDs based on PANI and polyaniline (PASA) are investigated in this thesis. The PANI/PASA thin film showed superior spectroelectrochemical properties compare to other ECDs reported here or elsewhere.

An electrode with single wall carbon nanotubes (SWCNTs) coating was tested as the substrate for an ECD based on poly[2-(3-thienyl) ethoxy-4-butylsulfonate] (PTEBS) to examine performance of the electrochromic polymer on a substrate other than an indium tin oxide (ITO) electrode. Compared to ITO, the SWCNT based device exhibited superior properties.

ISAM, Ionic Self Assembled Multilayers, Electrochromism, Layer-by-layer