(Invited) Conjugated Polymers in Redox Active Devices: Electrochromism As a Case Study

Abstract

Conjugated polymers provide a unique encompassing set of structurally tunable optical, electronic transport, and redox properties that allows their present and potential use in a host of applications which span, field effect transistors, light emitting diodes, solar cells and photodetectors, electrochromism, along with batteries and supercapacitors. Processing of these materials is carried out using a variety of solution methods including spin-coating, spray-coating, blade-coating, slot die coating and ink jet printing. In this lecture, we demonstrate how the optical absorbance spectra of electron-rich pi-conjugated polymers can be tuned to yield electrochromic materials of all colors that can be switched to highly transmissive forms as desired for absorptive/reflective (display type) and absorptive/transmissive (window type) devices. We will demonstrate how structural design and synthesis of fully conjugated polymers, along with mixing in polymer blends, has been used to complete the color palette of electrochromic polymers (ECPs) needed for subtractive color mixing. Colorimetric tuning (using the L*a*b* color space) using a combination of electron rich and poor units, in conjunction with employing subtle changes in steric strain or relaxation, allows for the enhancement of the neutral form color vibrancy, and the transmissivity of the oxidized forms. We have developed a set of fast switching, high contrast black and brown ECP blends. We use these brown blends to demonstrate the attractiveness of ECPs in window-type electrochromic devices (ECDs) as active materials in color changing eyewear.