Potential of magnetron sputtered magnesium fluoride containing thin films for the multilayer design of coloured coatings for solar collector glazing

In this work, the potential of magnetron sputtered magnesium fluoride (MgF2) and MgF2 containing composite coatings for coloured solar collector glazing is investigated. Coloured thin-film interference coatings on the reverse side of the collector cover glass give solar collectors an aesthetic appearance, which facilitates their integration into the building’s envelope. Hereby, integration means that the solar collector is no longer recognisable as technical device. Moreover, its appearance is the one of an architectural design element. Four years ago we showed that it is possible to match the colours of solar glazing with those of commercial sun protection glasses by means of thin-film optical filters. These filters are based on alternating high- and low-refractive index materials. Adding MgF2 or Mg–F–Si–O as a second low-refractive-index material enables even more flexibility and freedom to design coatings with a specific reflection colour, especially for bright colours. A novel concept of coloured filters involving MgF2 has been developed. They exhibit – independent of their colour hue – a uniform high solar transmittance 85–85.7% combined with a bright reflection. First results are very promising and confirm the future potential of MgF2-containing multilayers for coloured solar collectors.