Embedding Quaternary V1-x-ySrxWyO2 into Multilayer Systems to Enhance Its Thermochromic Properties for Smart Glass Applications

Smart window glazing technology possesses a great potential for reducing the overall energy demand in the building sector. Thin films based on thermochromic vanadium dioxide (VO2) are ideally suited as functional layers of thermochromic smart windows. VO2 itself exhibits a significant change in optical transparency and reflectivity in the infrared spectrum. However, the optimization of VO2-based thin films for application as intelligent window glazing is still ongoing. The improvement is rather tedious because the key parameters set by the application such as transmittance modulation Delta T-2500, luminous transmittance T-lum, solar transmittance modulation Delta T-sol, and transition temperature theta(c) affect each other. Codoping of VO2 with strontium (Sr) and tungsten (W) drives the parameters close to the desired range. However, the requirements set for the use as smart window coating cannot be fully met. Here, we show by a systematic comparison of simulations and experiments that embedding a layer of thermochromic V1-x-ySrxWyO2 between an optimized TiO2 buffer and a TiO2 antireflection layer already adds additional degrees of freedom to simultaneously fulfill all smart window requirements for the optical parameters Delta T-2500, T-sol, T-lum, and Delta T-sol. In particular, the luminous transmittance T-lum is improved by not less than approximate to 10% in such a trilayer structure.