Improvement of coloration properties of Ag deposition-based plasmonic EC device by precise control of shape and density of deposited Ag nanoparticles
Ag nanoparticles exhibit various colors depending on their localized surface plasmon resonance (LSPR). Based on this phenomenon, Ag deposition-based electrochromic devices can represent various optical states in a single device such as the three primary colors (cyan, magenta, and yellow), silver mirror, black and transparent. A control of the morphology of Ag nanoparticles can lead to dramatic changes in color, as their size and shape influence the LSPR band. In this research, we focused on the diffusion rate of Ag+ ion when Ag nanoparticles are electrochemically deposited. Consequently, well-isolated Ag nanoparticles were obtained due to slow growth rate by using an electrolyte with a low concentration of Ag+ ions, resulting in an improvement in the color quality of cyan and magenta. Additionally, spherical Ag nanoparticles were deposited in the same device by optimizing the voltage application conditions, which represented yellow and green colors. In particular, green coloration is a unique phenomenon because it can appear by the combination of two absorption peaks of LSPR. As a result of investigating the finite-difference time-domain method, it was observed that the LSPR band in the long wavelength region was originated from the effects of the connection between Ag particles.