Engineering gratings for light trapping in photovoltaics: The supercell concept

The question of the optimal surface structure for light trapping is widely debated in thin-film solar cell research. Here we propose a generic design approach that can tailor the strength of the diffraction orders of a periodic structure. Our approach is based on a supercell geometry that is able to suppress the low orders that do not couple into the quasiguided modes of the thin film. We demonstrate the concept theoretically and experimentally, showing that the supercell outperforms conventional gratings.