Metal/Polymer Back Reflectors with Diffraction Gratings for Light Trapping in III-V Solar Cells

We report on the fabrication, characterization and simulation of diffraction gratings for back contact reflectors in III-V solar cells. The gratings are designed for thin-film solar cells incorporating absorbers with bandgap slightly lower than GaAs, such as InAs/GaAs quantum dot or GaInNAs solar cells. Metal/polymer back reflectors with a blazed grating or a pyramid grating were fabricated by nanoimprint lithography. The gratings are compared in terms of diffraction ability, which is the feature responsible for increasing the absorption. The pyramid grating showed higher diffraction of light compared to the blazed grating. The diffraction efficiency measurements were in agreement with the numerical simulations. The model validation enables tailoring the properties of the reflectors for other type of solar cells by adjusting the optimal dimensions of the gratings for different wavelengths.