Multicolor Electrochromism Showing Three Primary Color States (Cyan–Magenta–Yellow) Based on Size- and Shape-Controlled Silver Nanoparticles

Inorganic electrochromic (EC) materials have various advantages for use in display devices. We demonstrate here a new multicolor EC device based on an electrochemical silver deposition mechanism. Ag nanoparticles electrochemically deposited on an electrode exhibit a wide variety of optical states based on their localized surface plasmon resonance (LSPR). As LSPR bands and the resultant colors change depending on the size and shape of the nanoparticles, morphological control of the Ag nanoparticles enables multiple color representation. In order to exploit this color variation in inorganic EC devices, we investigated the electrochemical deposition of size- and shape-controlled Ag nanoparticles by varying the surface morphology of the electrode and by applying a step voltage, which consisted of the application of two consecutive different voltages. Using only silver deposition, we have successfully achieved the first LSPR-based multicolor EC device that enables reversible color changes, including three primary colors—cyan, magenta, and yellow—as well as transparent, black, and mirror in a single cell.