Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows

Abstract

Vanadium dioxide (VO 2) is a widely studied inorganic phase change material, which has a reversible phase transition from semiconducting monoclinic to metallic rutile phase at a critical temperature of τ c ≈ 68 °C. The abrupt decrease of infrared transmittance in the metallic phase makes VO 2 a potential candidate for thermochromic energy efficient windows to cut down building energy consumption. However, there are three long‐standing issues that hindered its application in energy efficient windows: high τ c, low luminous transmittance (Tlum), and undesirable solar modulation ability (Δ Tsol). Many approaches, including nano‐thermochromism, porous films, biomimetic surface reconstruction, gridded structures, antireflective overcoatings, etc, have been proposed to tackle these issues. The first approach—nano‐thermochromism—which is to integrate VO 2 nanoparticles in a transparent matrix, outperforms the rest; while the thermochromic performance is determined by particle size, stoichiometry, and crystallinity. A hydrothermal method is the most common method to fabricate high‐quality VO 2 nanoparticles, and has its own advantages of large‐scale synthesis and precise phase control of VO 2. This Review focuses on hydrothermal synthesis, physical properties of VO 2 polymorphs, and their transformation to thermochromic VO 2(M), and discusses the advantages, challenges, and prospects of VO 2(M) in energy‐efficient smart windows application.