Spatially confined growth of VO2(M) nanoparticles with improved thermochromic property

Abstract

In the pursuit of VO2-based energy efficient smart window, high-temperature annealing is a common way to prepare well-crystallized VO2 nanoparticles (NPs) with reduced defect density. However, it is usually accompanied by the formation of oversized VO2 NPs due to Ostwald ripening, making unsatisfactory optical performances of VO2-based films. In this work, we reported a spatial confinement route via incorporating commercial fumed silica (FS) as space barrier during the process of annealing ultrafine γ-VOOH NPs, and the size of the obtained VO2 NPs could be reduced to ∼50 nm. Moreover, VO2 films based on the multilevel spatial confinement strategy exhibit outstanding optical performances with balanced solar regulation efficiency (ΔTsol ∼ 17.82 %) and luminous transmittance (Tlum ∼ 51.74 %). A simple dipping process could be carried out to enable a hydrophobic self-cleaning surface of the obtained VO2 films, which was meaningful for smart window applications. VO2@SiO2 core-shell structure, referring to a strong spatial confinement strategy, was also prepared via coating γ-VOOH NPs with SiO2 followed by annealing treatment. The top-level optical performances with ΔTsol of 20.46 % and Tlum of 44.26 % of VO2@SiO2/PVP films were achieved successfully. The spatial confinement strategy may inspire more facile and efficient processes for development of high-performance VO2 films for various applications.