High-Throughput Screening for Color in Electrochromic Devices

Color selection for the transition between two color states within an electrochromic device can be a difficult and drawn out process involving careful molecular design of the chromophore, synthesis, and purification, followed by reiteration of this procedure should the desired color not be achieved.  Here, we present a technique in which high-throughput screening of color for conjugated polymer electrochromics inside an electrochromic device.   The techique involves co-diffusion of a monomer that would produce a high bandgap conjugated polymer with a monomer that would produce a low bandgap conjugated polymer within a polyelectrolyte to generate a diffusional gradient of both monomers between their points of introduction.  This diffusional gradient of monomers is then converted to a gradient of random copolymers via an electrochemical oxidation producing nearly the entire subtractive spectrum of colors that can then be switched to a colorless state.  Perpendicular orientation of this gradient to the electrochromic device allows for achievement of neutral coloration, important for tinting applications.  Electrochromic devices of 171 cm² active switch area have been optimized through optimization of the polyelectrolyte, and monomer choice for our solid-state conversion process of monomers to conjugated polymers to result in photopic contrasts as high as 58% without any substrate corrections.  Photopic contrasts of 41% have been achieved for devices meeting military neutrality standards.  As a further demonstration of our solid-state conversion, we have prepared all-spandex electrochromic devices in which the electrochromic device can be stretched during the color-change process.  The spandex devices have the feel of spandex and could find applications in wearable displays and/or adaptive camouflage.