Electrochemical Analysis of Optical Switchable Filter with a NiO Thin Film for High-Performance Incubators

Abstract

We report an optical switchable light filter fabricated from all solid-state materials for use in preterm infant incubators. The nickel oxide (NiO) thin film in the filter was fabricated by magnetron sputtering. Conventional NiO thin films are often dipped in a solution to produce a nickel hydroxide thin film; however, our as-prepared film was stored in a thermostat/humidistat bath at 50 °C and 80% relative humidity to create the nickel hydroxide thin film instead, according to the electrochromic (EC) principle. The properties of the NiO thin film were also investigated. The optical switchable light filter also contained a W-Ir-O thin film, because the widely used WO3 thin film shows an unsuitable EC color change to dark blue. The W-Ir-O thin film did not absorb the longer wavelengths in the visible range, which is required for incubators. The optical switchable light filter containing the NiO thin film changed between pale yellow and dark yellow when a voltage was applied. The optical switching speed from the pale yellow to dark yellow state was around 60 s, and the reverse process was around 60 s. The fabrication of filters with a suitable color change for incubators requires further investigation.