Nanoporous Thermochromic VO2 (M) Thin Films: Controlled Porosity, Largely Enhanced Luminous Transmittance and Solar Modulating Ability

Vanadium dioxide is the most widely researched thermochromic material with a phase transition temperature (tau(c)) of around 68 degrees C, and its thermochromic performance can be enhanced by adding nanoporosity. Freeze-drying has been employed to fabricate nanostructures with different porosities from 16 to 45% by varying the prefreezing temperature and precursor concentration. The luminous transmittance (T-lum) and solar modulating ability (Delta T-sol) are greatly enhanced as a result of increasing pore size and pore density. The freeze-dried sample with 7.5 mL of H2O2 precursor dip-coated at 300 mm/min gives the best combination of thermochromic properties (T-lum approximate to 50%, Delta T-sol = 14.7%), which Surpasses the best combined thermochromic performance reported to date that we are aware of (T-lum approximate to 41%, Delta T-sol = 14.1%).