Antireflective Coatings

Solar module with porous SiO2 anti-reflective coating
© K. Dobberke for Fraunhofer ISC
Solar module with porous SiO2 anti-reflective coating

There are basically three different strategies for the antireflection coating of surfaces: With λ/4‑layers, a material is used whose refractive index is between that of the substrate and that of the environment. Such layers are optimally anti-reflective when their thickness equals to ¼ of the wavelength of the incident light. The required refractive indices can only be achieved with porous films of e.g. SiO2 or MgF2.

An antireflective interference surface consists of a sequence of high and low refractive materials, in practice at least three layers are required.

In a so-called moth's eye, nanostructures taper from the substrate to the environment, which results in a continuous refractive index gradient. To avoid optical scattering, the structure size must not exceed 1 µm.

In practice, the respective advantages and disadvantages such as optical performance, mechanical stability and manufacturing costs must be weighed against each other. All described strategies can be realized by wet chemical processes.

Principles of optical anti-reflection coating of surfaces

Optical anti-reflection coating of surfaces
© Fraunhofer ISC