Enhanced Luminous Transmission and Solar Modulation in Thermochromic VO2 Aerogel-Like Films via Remote Plasma Deposition

Abstract: Vanadium dioxide (VO2) is a thermochromic material that undergoes a phase transition from a monoclinic semiconducting state to a rutile metallic state at 68 degrees C, a temperature close to room temperature. This property makes VO2 particularly valuable in applications such as optical and electrical switches, data storage, neuromorphic computing, and remarkably dynamic smart windows for solar radiation control. VO2 typically needs to be synthesized for these applications as nanostructured thin films. Over the past few decades, significant efforts have been made to control the thermochromic properties of VO2 through crystal structure tuning, doping, and the development of VO2 nanocomposites. Additionally, introducing nano- and mesoporosity has been shown to enhance the optical properties of thermochromic VO2 films. This study presents a methodology for producing highly porous, aerogel-like V2O5 films, which can be thermally processed to form aerogel-like VO2 films. This process is based on sequential plasma polymerization and plasma etching to produce aerogel-like V2O5 films that are annealed to yield ultraporous nanocrystalline VO2 films. The sacrificial vanadium-containing plasma polymers are obtained by remote plasma-assisted vacuum deposition (RPAVD) using vanadyl porphyrin as a precursor and Ar as plasma gas. The aerogel-like VO2 films show exceptional thermochromic performance with luminous transmittances higher than 54%, solar modulation up to 18.8%, and IR modulation up to 35.5%. The presented plasma methodology is versatile, allowing both the synthesis of VO2 plasmonic structures to enhance the thermochromic response and the encapsulation of films to improve their stability in air dramatically. Additionally, this solvent-free synthetic method is fully compatible with doping procedures, scalable, and holds great potential for designing and optimizing smart window coatings.