Tracking the optical constants of self-patterned VO₂-based on smart windows during metal-insulator transition

Vanadium dioxide (VO₂) is widely recognized as a thermochromic material with enormous potential for application in smart windows for energy-efficient buildings. In this study, a bottom-up self-patterning approach was illustrated to fabricate the VO₂ films with different thicknesses, which exhibited enhanced luminous transmittance (T_lum) and enlarged solar modulation ability (ΔT_sol). By tracking the optical constants of the films throughout the thermochromic process, the changes generated at the microscopic level in the material could be associated with its macroscopic behavior when utilized as an energy-saving material. The results revealed that changing the film thickness affected not only the electron occupancy on V 3d-O 2p hybrid orbitals but also the electron-electron correlation energy and the associated band gap, which modulated the metal-insulator transition behavior and regulated the luminous transmittance.