We present prototypes of a new and unique class of thermochromic “motheye smart window” that exploits the material properties of vanadium dioxide to passively modulate the transmission of solar energy into a building. In addition, we will discuss the theoretical performance boundaries for a variety of vanadium dioxide smart window geometries.
The optical properties of vanadium dioxide are significantly enhanced when coated in thin layers over a nano-structured surface. Benchmarked against a planar geometry, maximum solar energy transmission modulation (the critical factor in assessing energy saving potential) is increased from 10% to almost 25% using this approach. This ranks the motheye geometry amongst the very highest performing VO2 smart window classes.
Graded refractive index 'motheye' antireflection surface structures, inspired by nature, are chosen for both their optical and wetting enhancements. Our window surfaces are designed to efficiently transmit visible light over a wide range of angles (insensitive to the light’s polarisation) whilst maintaining strong solar-thermal energy modulation, facilitating good energy saving. In addition, the high aspect ratio structures modify the hydrophobicity of the surface making it robustly super-hydrophobic which lends the window surface the ability to self-clean.
We will present our methods for fabricating the nano-structured glass surface using self-assembled colloidal lithographic methods. Optical and wetting performance tests of our devices will be presented and discussed.