It is to be noted that the mc-Si:H bottom cells are in both case nominally the same and the systematic difference in Jsc is related to the thickness of the filter layer not perfectly matching the top cell absorption. The FF in tandem cells does not continuously increase with increasing filling layer
thickness as for the filtered bottom cells, however this evolution is not fully understood. Increasing the filling layer thickness does not lead to poorer ZnO sheet resistance thus excluding an increase of serial resistance as a cause of poor FF. The Jsc losses can be understood considering the changes in ARS with increasing filling layer thickness leading to a poorer light scattering toward large angles as shown in Fig. 8