Plasmonic thin films for application in improved chromogenic windows

Nanocomposites consisting of noble metal nanoparticles in a transparent matrix exhibit plasmonic absorption in the visible wavelength range, and conducting oxide nanoparticles display a localized plasma absorption in the near infrared. The optical properties of nanocomposites are commonly modelled by effective medium theories, which describe the effective dielectric function of the composite using as input the dielectric functions of the constituents and their respective volume fractions. Plasmonic effects can be exploited in the design of energy-efficient windows in order to obtain improved performance. Electrochromic coatings that switch in the near infrared make use of the modulation of the plasma absorption of oxide nanoparticles due to charge density modulation induced by an external voltage. Plasmonic thermochromic switching in the near infrared has the potential to be significantly larger than in the case of a thin film. Very thin noble metal films are an interesting alternative to conducting oxides as transparent contacts to electrochromic devices. However, in this latter case plasmonic effects are to be avoided rather than exploited. (paper)