Flexible Molecular Electrochromic Devices Run by Low‐Cost Commercial Cells

TLDR

Low‑cost electrochromic materials are in high demand for visible‑region multicolor displays, paper‑based, flexible, wearable electronics, smart windows, and optoelectronic applications. The authors aim to fabricate large‑scale, high‑yield, robust polyelectrochromic devices on rigid to flexible ITO substrates using an anthracene‑containing viologen (AnV₂⁺) and polythiophene (P3HT). They achieve this by incorporating anthracene groups into viologen to prevent cation‑radical dimerization, fabricating the devices on ITO substrates, testing them with low‑cost commercial cells, and using computational studies to interpret the results. The devices exhibit three reversible visible color states with sub‑second to second switching times (0.7–1.6 s), high coloration efficiency (484 cm²/C), and cycling stability of 9,000 s (3,000 cycles), while AC impedance confirms that P3HT enhances charge transfer to AnV₂⁺, demonstrating CMOS compatibility and paving the way for cost‑effective flexible and wearable electrochromic devices.

Abstract

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 AnV 2+ ), 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 cm 2 /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 AnV 2+ . This work shows CMOS compatibility and can pave the way for developing cost‐effective flexible and wearable electrochromic devices.