Effect of annealing condition on the crystallinity of VO₂ (β) thin-films fabricated by a solution-based process

Vanadium dioxide (VO₂) is the core material for thermochromic smart windows, which can control near-infrared light while maintaining visible light transmittance in response to ambient temperature. This study is an experiment that can shorten the time to make a thermochromic thin-film using nanoink containing VO₂ powder. VO₂ (β) particles were synthesized via hydrothermal synthesis using V₂O₅ as the raw material and oxalic acid as the reductant. Thin-films were prepared by a solution-based process using nanoink, which contained VO₂ (β) powder with polyvinylpyrrolidone and ethyl cellulose in a solvent of water and ethanol. Only VO₂ (R/M) undergoes a fully reversible metal-insulator transition. Therefore, annealing conditions that can change VO₂ (β) to VO₂ (M) while removing the polymer on the thin-film surface are required. A VO₂ (β) thin-film was successfully converted to VO₂ (M) when annealed at 800 °C for 1 h, and the intrinsic properties of VO₂ (M) were found in optical results.