Multilayer front-sheet for solar modules with tuned color appearance

The acceptance of solar cells in the built environment is partly dependent on the appearance of the solar modules. One aspect in the appearance is color. In most cases a solar cell itself reflects either blue or no color and will appear blackish. For the blue solar cells it is possible to tune the antireflection layer in such a way that a different color is reflected. We propose a front-sheet covered with a stack of thin layers consisting of high and low refractive index materials deposited from sol-gel onto PET foil such that only a particular wavelength range is reflected. We show through modeling that by alternating layers consisting of low refractive index layer (silica (SiO 2) and high reflection layer (silica-titania 25 mol% SiO2: 75 mol%TiO2) on PET foil such color reflection can be achieved. In modeling exercises the influence of the number of layers, thickness variations and angle of incidence on the reflected color are predicted as well as an estimated influence on the module efficiency. We show that with a four layer stack we can reach chroma values of 60 for green and 40 for red color in the CIELCH system. In experimental results we achieve a peak reflection of 41.7% with a band width of 90 nm while transmission is more than 90% for the other parts of the spectrum. © 2011 SPIE.