A self-patterning multicolor electrochromic device driven by horizontal redistribution of ions

Electrochromic devices (ECDs) displaying multicolor patterns have attracted great interests in a wide range of applications. Considering the complexity in the integration of various EC materials and multi-electrode configurations, the design of multicolor patterned ECDs based on simple approaches remains an elusive goal. Here, we present a self-patterning ECD based on a single layer of multicolor polyaniline (PANI) film. The device demonstrates a novel and simplified three-layer structure including PANI layer, gel electrolyte and conducting layer, which is distinguished from conventional EC devices with typical five layers. Furthermore, a working principle responsible for the self-patterning is proposed based on the horizontal movement and redistribution of anions in PANI layer driven by a current. This unique ionic transport mode contributes to the formation of a multicolor pattern composed of three segments. The dynamic variation of the pattern could be achieved by changing the direction and strength of the current, from which the device exhibits a high transmittance contrast of -60% at 630 nm, fast response rate (similar to 16 s) and good cycling performance. It is envisioned that this work may provide a new insight to develop self-patterning ECDs for wide applications in information displays, smart fabric and military camouflage.