Si incorporated diamond-like carbon film-coated electrochromic switchable mirror glass for high environmental durability

Electrochromic switchable mirror glass is promising for energy-saving windows because it changes between a reflective and a transparent state when a voltage is applied. In our previous work, we confirmed that the device degraded at high temperatures and high relative humidity using an accelerated degradation test. The degradation was related to the reaction of the moisture in atmosphere with the surface optical switching layer of the Mg–Ni thin film. Therefore, we have developed a device with a Si incorporated diamond-like carbon thin film surface layer to improve the environmental durability. When the device was kept in a simulated environment at a constant temperature of 40 °C and a constant relative humidity of 60%, optical and atomic force microscopy showed that the surface did not degrade. Moreover, the surface coating repelled water, which prevented the reaction of the moisture with the Mg–Ni thin film. The optical switching speed from the transparent state to the reflective state of the device was slower than that of the uncoated device because of the fabrication conditions. The result seems to be related to the surface of the Mg–Ni layer which might be damaged by the conditions.