Phase transition behavior and optical properties of F/Mo co-doped VO2 for smart windows.

To meet the demand for smart windows, element doping is widely used as a powerful tool to customize the thermochromic properties of vanadium dioxide (VO 2). Here, Mo-doped and F/Mo co-doped VO 2 nanoparticles (NPs) are synthesized by the supercritical hydrothermal method. Doped VO 2 films show excellent thermochromic properties including the reduced phase transition temperature (T c = 47.4 °C), enhanced luminous transmittance (T lum = 59.7%), and high solar energy modulation (ΔT sol = 13.7%). Both X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) are utilized to study the local structure and chemical valence of the vanadium and molybdenum in the VO 2 lattice. Combined Mott's with Peierls's models, the phase transition behavior of the doped VO 2 is revealed deeply, i.e., depending on the octahedral symmetry and charge transfer. Additional electron injection seems to play a more important role than structural distortion in decreasing T c , and F atoms exhibit a higher modulation ability of T c. In addition, reduced reflectance by doping is responsible for the significantly improved T lum , while ΔT sol is found to be more sensitive to the film structure. This work uncovers the mechanism behind the phase transition of Mo-doped and F/Mo co-doped VO 2 NPs, which is expected to inspire the optimization strategy of element-doped VO 2 films served as smart windows. • Mo-doped and F/Mo co-doped VO 2 nanoparticles (NPs) are hydrothermally synthesized. • Doped VO 2 films possess excellent thermochromic properties. • Phase transition behavior is depended on octahedral symmetry and charge transfer. • Increased T lum is attributed to the reduction of film reflectance. [ABSTRACT FROM AUTHOR]