Inkjet printing of 2D polyaniline for fabricating flexible and patterned electrochromic devices

Conjugated organic polymer (COP)-based electrochromic devices (ECDs) exhibit promising applications in digital and color displays. However, fabricating COP-based ECDs integrated with excellent electrochromic performance, customized patterns, and flexibility remains challenging. In this study, we report inkjet-printed, flexible, and patterned ECDs based on two-dimensional (2D) polyaniline (PANI) sheets, which are evenly dispersed in formic acid (FA) enabling high-precision, stable inkjet printing. The pristine lamellar structure of PANI sheets, which combine nanoscale thickness and an appropriate doping ratio, and the additive-free ink composition endow the printed PANI electrodes and ECDs with high performance. The fabricated PANI electrode exhibits a high optical contrast (76% at a wavelength of 750 nm), a good coloration efficiency (CE) of 259.1 cm2 C−1, and a short coloration/bleaching time (1.8/2.4 s), simultaneously integrated with pseudocapacitance and mechanical flexibility. Moreover, the 2D lamellar PANI ink developed in this study can be printed into various designed patterns, particularly for electrochemically controlled, addressable electrochromic displays. This work highlights 2D lamellar PANI as a promising electrochromic material for flexible and patterned ECDs.