Multicolor electrochromic device based on reversible metal electrodeposition of Bi-Cu with controlled morphology and composition ratio

Abstract

Reversible metal electrodeposition (RME) devices with optical tunability in multiple optical states are exciting alternatives to conventional electrochromic (EC) smart windows. In this work, we studied Bi-Cu electrodeposition carefully by applying the step-potential method and constant-potential method. Five optical states—transparent, purple transparent, purple mirror, yellow transparent and yellow mirror—are achieved, which is firstly reported in Bi-Cu RME devices. The acquisition of polychromatic states could be attributed mainly to the localized surface plasmon resonance (LSPR) effect, which is related to morphologies and composition ratios of the electrodeposited bimetal films. Our device exhibits excellent cycling stability switched between purple transparent state and transparent state, maintaining 80% transmittance window after 2500 cycles. The yellow mirror state generated by the step-potential method shows superior color retention stability and heat blocking ability than the purple mirror state generated by the constant-potential method, meaning that the more uniform and denser metal film deposited by the step-potential method is more suitable to the EC applications. In brief, Our RME device exhibits multiple optical states, competitive switching speeds, superior cycling stability, color retention stability and heat blocking ability, making it promising for use in light modulating devices, such as smart windows and information displays.