Solvothermal synthesis and characterization of highly monodisperse organically functionalized vanadium oxide nanocrystals for thermochromic applications

Highlights: • Vanadium oxide nanocrystals is synthesized via an improved solvothermal method. • Vanadium oxide nanocrystals possess a structure of distorted paramontroseite VO₂(P). • Thermally annealed nanocrystal thin films exhibit good thermochromic properties. - Abstract: We report on the synthesis and characterization of highly monodisperse organically functionalized vanadium oxide (VO_x) nanocrystals with a size of 7–10 nm. We show that how these nanocrystals can be prepared by an improved solvothermal reaction and confirm their composition and structure through various materials characterization techniques. Our results revealed that VO_x nanocrystals have a crystalline structure almost identical to that of paramontroseite VO₂(P) and the majority of vanadium is in oxidation state of V(IV). VO_x nanocrystal films can be readily prepared via a spin coating technique. Once thermally annealed at ∼350 °C under an air/N₂ flow, the films exhibited good thermochromic properties (luminous transmittance (T_lum) ≈49–66%, infrared switching efficiency (ΔT_2000nm) ≈28–43%, and solar modulating ability (ΔT_sol) ≈7.4–10.7%), corresponding to a phase transition between monoclinic VO₂(M) and rutile VO₂(R).