Broadening thermochromic switching into the visible and NIR by incorporating Au-doped TiO2 beneath VO2 films

We report a multilayer architecture in which Au nanoparticles embedded in a crystalline anatase TiO2 matrix are incorporated beneath VO2 thin films. This configuration promotes the formation of the monoclinic VO2 (M1) phase and enhances the thermochromic performance of the system. Reflectance and absorbance analyses demonstrate a broadened hysteresis response that extends beyond the conventional NIR domain into the VIS range. Moreover, a clear correlation between optical hysteresis and bandgap evolution was established, providing insight into the interplay between Drude free-carrier contributions and interband transitions during the metal–insulator transition. These findings highlight a promising pathway for tailoring VO2-based thermochromic coatings with dual near-infrared–visible switching capability, offering great potential for energy-efficient smart coatings, wavelength-selective optical devices, and advanced photonic applications.