Thermochromic Smart Windows for Energy Saving and Comfort in Buildings and Vehicles

Thermochromic materials are such being able to change their optical properties in response to temperature change. Nano-scaled thermochromic material can result in novel properties and widen applications. Vanadium dioxide is one of the most useful thermochromic materials, characteristic of a reversible semiconductor-to-metal phase transition at a temperature near the ambient. We have been studied this unique material for over 20 years to develop a thermochromic “smart window” for energy saving and comfort for buildings and vehicles. Multiple approaches have been achieved to fulfill the goal: 1) multifunctional structure using thermochromic VO₂ and photocatalytical TiO₂ was deposited on float glass by magnetron sputtering, which shows excellent solar control and self-cleaning performance; 2) a polymer-aided deposition method has been established with the performance even superior to the best film by sputtering; 3) mass production of high quality VO₂-based nano-particles have recently been established in Japan (AIST) and China (SICCAS), and thermochromic polymer foil was produced for the first time. Optimization of the VO₂ nanoparticle/polymer foil system was done using the effective medium theory, which demonstrates an ever high energy modulation. This talk will present a review to the state-of-the-art of smart windows, with focus mostly on thermochromic ones both in China and Japan.