Conventional selective low-e coatings for windows of residential buildings have a cut-off frequency in the near infrared spectral region NIR, limiting the resulting solar heat gain coefficient to g ≈ 0.5. By structuring the coating into micro-/nanomeshes, the selectivity shall be enhanced and higher solar heat gains shall be achieved. The resulting increase in solar heat gains will lead to energy savings in heating in the residential sector.
In addition to this, metal nanomeshes will also allow to replace the transparent conductive oxide layer in electrochromic windows, reducing the needs for indium, and leading to higher switching speed and switching homogeneity by an improved lateral charge transport.
All switchable window technologies are based on transparent conductive electrodes, which are currently made from transparent conductive oxides (TCOs). Indium tin oxide (ITO) belongs to the TCOs with the highest performance regarding the trade-off between transparency and electrical conductivity. With the widespread use of screen and display technologies, and the growing market of photovoltaics, the demand of indium is constantly increasing. However, indium is one of the scarcer elements, at least in terms of average abundance in the Earth’s crust. Metallic micro-/nanomeshes are an interesting emerging alternative to transparent conductive oxides, because the micro-nanomeshes combine high transparency with electrical conductivity.
For short-wavelength radiation in the spectral range of solar radiation (VIS-NIR), the openings are comparatively large to the wavelength, and the electromagnetic wave is transmitted. Therefore the nanomesh is transparent.
For long-wavelength radiation in the spectral range of thermal radiation, the dimensions of the openings are comparable to the wavelength, and the electromagnetic wave is reflected. Therefore the nanomesh is an infrared-reflector and the surface with the nanomesh has a low thermal emissivity.
Electricity is conducted in the nanowires of the mesh. Therefore the nanomesh can be used as transparent electrode.
Approaches for the fabrication of metallic micro-nanomeshes are laser engraving, self-assembly and UV/electron beam lithographies.
Starting PhD thesis in this domain
J. Fleury, tentative title of PhD thesis: Transparent Nanomeshes for smart windows,