Dual n- and p-Type Dopable Electrochromic Devices Employing Transparent Carbon Nanotube Electrodes

We report on the use of highly transmissive single-walled carbon nanotube (SWNT) films as electrodes in electrochromic devices that employ a dual n - and p -type dopable donor−acceptor polymer, poly[5,8-bis-(3-dihydro-thieno[3,4- b ][1,4]dioxin-5-yl)-2,3-diphenyl-pyrido[3,4- b ]pyrazine], or poly(bisEDOT-PyrPyr-Hx 2 ). This low bandgap polymer is capable of repeated, stable electrochemical cycling between a neutral form and both an oxidized, p- doped state and a reduced, n- doped state. The ability of this electrochromic material to exhibit a stable n -type doped state enabled the construction of an absorptive/transmissive dual-window electrochromic device showing optical changes over a broad energy range—from the mid-infrared to the visible region. This absorptive/transmissive dual polymer electrochromic device is unique in that it exhibits electrochromism utilizing the same polymer as both the cathodically and anodically coloring material. Infrared electrochromic behavior was achieved with the use of SWNT films due to their high transmissivity in the near to mid-IR (1−3 μm). Initial results studying the long-term redox switching stability of the absorptive/transmissive poly(bisEDOT-PyrPyr-Hx 2 ) ECD demonstrate that the system can be repeatedly cycled (>2,000 cycles) and maintain a high optical contrast in the near-infrared (32% at 2000 nm).