Effect of feature size on the reflective behaviour of the MorphoColorTM concept

The MorphoColor concept for highly efficient colored solar modules aims to improve the acceptance of those modules in visible areas like roofs and facades. The core of the MorphoColor technology is the combination of a structured substrate with a spectrally selective reflecting layer stack. The work presented within this manuscript investigates the effect of using an aperiodic substrate structure whose characteristic feature size is in the same order of magnitude as the wavelength of visible light. Representative pseudo-aperiodic structures were arranged using rigorous coupled-wave analysis. By combination of these structures with a layer stack, a fully wave optical model of this realization of the MorphoColor concept could be established. The characteristic feature width and height have been varied in this model, resulting in lower limits for the efficacy of the concept in both parameters. For slanted incidence, a significant change of the reflected spectrum was observed. To explore this effect, a model representing infinite feature sizes was developed by independently combining the effects of a refractive system with equal properties to the one used within the first model and a plain layer stack. The comparison of results obtained from both methodes showed that the usage of small features leads to additional effects that can be attributed to the interaction of structure and layer stack. The magnitude of these effects increased with increasing incident angle on the surface and leads to a reduced spectral selectivity of the reflection.