Switchable window based on electrochromic polymers
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A large contrast ratio (>⌬⌻ ⳱ 60%) and rapid switching (0.3–1 s) electrochromic (EC) polymer device that consists of a laminated two-layer structure between two electrodes was prepared. The new design consists of an indium tin oxide (ITO) glass electrode, a cathodic EC polymer film, a solid electrolyte, and a counterelectrode that replaces the anodic EC polymer and ITO electrode. Four EC polymers including two new EC polymers, Poly[3-methyl-3⬘-propyl-3,4-dihydro-2H-thieno(3,4-b)(1,4)dioxepine] (PProDOT-MePro) and Poly[3,3-diethyl-3,4-dihydro-2H,7H-(1,4)dioxepino(2,3-c)pyrrole] (PProDOP-Et2), were synthesized as cathodic EC polymers. A carbon-based counterelectrode was prepared for comparison with an Au-based counterelectrode. Several kinds of polymer gel electrolytes were prepared for comparison. The devices (windows) were increased in area from 0.028 × 0.04 in.2, 1 × 1 in.2 to 3 × 3 in.2 Three main components, the EC polymer film, the gel electrolyte, and the counterelectrode, were studied and their optical properties, conductivities, and repeatabilities were compared. The effects of window size on the contrast ratio, switching speed, power usage, and repeatability were studied.
I. INTRODUCTION
Switching technology is a continuously growing field due to its current and potential applications for architectural, vehicular, and aircraft windows, skylights, sunroofs, eyeglasses, and numerous types of displays.1,2 Whether its purpose is for energy conservation, functional use, or purely aesthetic, switchable devices have a promising future. Generally, these devices can be categorized into three main groups based on the active material present: suspended particles, liquid crystals, and electrochromics.3 On a macroscopic structure level, the device design is the same for all three groups: an active material (liquid crystal medium, suspended particle or electrochromic material) is sandwiched between two electrodes. When a potential is applied, the optical properties of the devices change. However, on a microscopic level, the switching mechanisms are quite different. To use switching devices for practical applications, it is imperative that the devices demonstrate large contrast ratios, rapid switching, repeatability, and an overall robust design. Here, a comparison between three main switching devices is presented regarding their resulting performance. One recent design has surfaced to minimize some of of the constraints of liquid crystal displays (LCDs). Polymer-dispersed liquid crystal (PDLC) devices include
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0259 2072
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 7, Jul 2004 Downloaded: 13 Mar 2015
an active layer composed of liquid crystal droplets encapsulated within a transparent matrix. The on-off switching states yield a translucent white state and a transparent state, respectively. The transparency of the device is greatly improved because no polarizer is needed. Also, manufacturing constraints a
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