Flexible Molecular Electrochromic Devices Run by Low-Cost Commercial Cells

Abstract

The present era has seen tremendous demands for low-cost electrochromic materials for visible-region multicolor display technology, paper-based, flexible, and wearable electronic devices, smart windows, and optoelectronic applications. Towards this goal, the authors report large-scale, high-yield and robust polyelectrochromic devices fabricated on rigid to flexible ITO substrates comprising novel anthracene containing viologen, (1,1″-bis(anthracen-9-ylmethyl)-[4,4″-bipyridine]-1,1'-diium bromide, abbreviated as AnV2+), and polythiophene (P3HT). Interestingly, the devices show three states of reversible visible color in response to the applied bias, sub-second to second switching time (0.7 s/1.6 s), high coloration efficiency (484 cm2/C), and longer cycling stability up to 9,000 s (3,000 switching cycles). Introduction of the anthracene moieties to viologen inhibits the formation of an undesired dimer of cation radicals in response to the applied bias, otherwise the device's color-switching would be hampered when the bias polarity is reversed. The fabricated electrochromic devices are tested with commercially available low-cost cells to perform—a unique approach toward practical applications. The computational study facilitates the understanding of experimental results. Alternating current (AC)-based electrical impedance spectroscopy reveals that P3HT facilitates enhanced charge transfer to AnV2+. This work shows CMOS compatibility and can pave the way for developing cost-effective flexible and wearable electrochromic devices. © 2023 Wiley-VCH GmbH.