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

Vanadium dioxide (VO₂) is a thermochromic material that undergoes a phase transition from a monoclinic semiconducting state to a rutile metallic state at 68 °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. Additional reference compact films VO₂ films are obtained by a direct RPAVD process using the same precursor and oxygen plasmas in combination with thermal annealing. 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.