The first Janus‐structured electrochromic devices are evolved from traditional electrochromic structures by inserting an optically thin (4–8 nm) metallic layer with complex refractive index. These unique differentially colored devices are used to mimick the butterfly Kallima inachus, which closely resembles a dry leaf when its wings are close and exhibits various bright colors when its wings are open.
Abstract
Some butterfly species such as the orange oakleaf (Kallima inachus) have strikingly different colors on the dorsal (front) sides of their wings compared to those on the ventral (back) sides of their wings, which helps camouflage the butterflies from predators and attract potential mates. However, few human‐made materials, devices, and technologies can mimic such differential coloring for a long time. Here, a new type of Janus‐structured two‐sided electrochromic device is developed that, upon application of different voltages, exhibits a coloration state on one side that is distinctly different from that on the other side. This is achieved by inserting an optically thin (4–8 nm) metallic layer with a complex refractive index, such as a layer composed of tungsten, titanium, copper or silver, into typical electrochromic structures.