Surface treatment of VO₂ films with enhancing the modulation of phase transition and thermochromic performance

As a typical phase transition material, vanadium dioxide (VO2) exhibits a promising candidate in the thermochromic field, while the relatively high critical temperature, low luminous transmittance and poor near-infrared modulation impede its practical application. Herein, we propose a facile strategy to overcome the challenges above. The critical temperature of VO2 films gradually reduced as the phosphating temperature increased and became a metallic state even below 2 kelvin. Combining with the first-principles calculations, the mechanism that P-doping induced the metal-insulator transition of VO2 was ascribed to the increment of itinerant electrons, and the migration of the energy band that moved toward the Fermi level. Optical performances demonstrated that the near-infrared modulation ability reached 19.3 %, while there was a 12.1 % improvement in luminous transmittance after the appropriate phosphating process of VO2 films. Meanwhile, the thermal emissivity value greatly decreased from 0.83 to 0.56. The current findings not only offer a novel strategy to boost the thermochromic characteristics of VO2, but also bring insight into a comprehensive understanding of the mechanism of phase transition in VO2.