Bioinspired Multifunctional Vanadium Dioxide: Improved Thermochromism and Hydrophobicity

Vanadium dioxide (VO2) films with moth-eye nanostructures have been fabricated to enhance the thermochromic properties with different periodicity (d) to achieve antireflection (AR). It is revealed that the films with smaller d (210 and 440 nm) could increase both the luminous transmission (T lum) and infrared transmission (T IR) at 25 and 90 oC, as the d is smaller than the given wavelength and the gradient refractive index produces antireflection. The average T lum and T IR of VO2 increase with decreasing d. Compared with the planar film, the AR sample with periodicity of 210 nm and thickness of 140 nm can offer approximately 10% enhancement of T lum and 24.5% increase in solar modulation (ΔT sol). With the addition of hydrophobic overcoat on the patterned VO2, ∼120° contact angle could be achieved. The present approach can tailor the optical transmittance in different wavelengths at high and low temperature together with self-cleaning, opening new avenues for producing hydrophobic VO2 with enhanced thermochromic properties for smart window applications.