Degradation Analysis of Electrochromic Switchable Mirror Glass Based on Mg–Ni Thin Film at Constant Temperature and Relative Humidity

Abstract

An electrochromic mirror glass that can be switched between reflective and transparent states by voltage application is presented. For the practical applications of such a device such as in energy-saving windows, optical devices, and electronic devices, the effects of environmental factors such as temperature and humidity on the optical switching properties of the device should be investigated in detail. In this work, the effects of constant temperature and relative humidity conditions on the device properties were studied. In particular, surface analysis studies were conducted. When these devices were kept at 40 °C and 60% relative humidity (RH), the speed of switching from the reflective state to the transparent state decreased with increasing time of storage in the bath. This reduced switching speed was related to the degradation of the surface metallic layers of the device, which could be observed by transmission electron microscopy (TEM) as an increase in surface roughness (Ra = 19.8 nm). Although the as-prepared device had a Mg4Ni optical switching layer approximately 40 nm in typical thickness, the degraded device exhibited an expanded layer of approximately 78 nm thickness. This increased thickness was associated with the change to the nonmetallic states of oxide and hydroxide from the metallic states of magnesium and nickel in the layer because of the adverse effects of the atmosphere.