Spectral properties of intermediate reflectors in micromorph tandem cells

In thin-film silicon tandem solar cells consisting of amorphous and microcrystalline silicon, efficiency enhancements can be achieved by increasing the current density in the a-Si:H top cell. Therefore, it is necessary to provide an optimized current matching at high current densities for both junctions. We present a numerical method to obtain suitable intermediate reflections achieving optimal current-matched tandem cells. We used idealized and measured reflection spectra of spectrally-selective intermediate filters for the current matching. For the optical design of such intermediate reflective layers a prediction of the spectral properties towards optimal current matching is presented.