Flexible Pseudocapacitive Electrochromics via Inkjet Printing of Additive-Free Tungsten Oxide Nanocrystal Ink

Abstract Direct inkjet printing of functional inks is an emerging and promising technique for the fabrication of electrochemical energy storage devices. Electrochromic energy devices combine electrochromic and energy storage functions, providing a rising and burgeoning technology for next-generation intelligent power sources. However, printing such devices has, in the past, required additives or other second phase materials in order to create inks with suitable rheological properties, which can lower printed device performance. Here, tungsten oxide nanocrystal inks are formulated without any additives for the printing of high-quality tungsten oxide thin films. This allows the assembly of novel electrochromic pseudocapacitive zinc-ion devices, which exhibit a relatively high capacity (≈260 C g−1 at 1 A g−1) with good cycling stability, a high coloration efficiency, and fast switching response. These results validate the promising features of inkjet-printed electrochromic zinc-ion energy storage devices in a wide range of applications in flexible electronic devices, energy-saving buildings, and intelligent systems.