Figure 1a shows the measured cell efficiencies on cells with three different rear bus bar pastes. We compare
cells with a reference paste (60 % silver content) with two batches with silver reduced pastes (Paste A and B: ~ 40
% silver content). Paste A shows a higher efficiency than the reference paste, which we attribute to the inherent
variation in the production line. Paste B shows a drop in measured efficiency which is due to the increased line
resistance. Figure 1b shows the measured fill factor FF of the cells. Reference cells and cells with paste A get a fill
factor FFref = FFA = 77.6 % whereas cells with paste B loose around 0.5 % getting a fill factor FFB = 77 %. Thus
the silver reduction has no influence on the series resistance, regarding the result of paste A. The fill factor loss of
paste B is based on a different paste recipe, resulting in an increase of the series resistance and thus a drop in fill
factor. Figure 1c presents the measured Voc values of the cells. The figure shows a slight variation in Voc between
the batches. We explain this variation with variations in the production line. Nevertheless Voc values Voc > 625 mV
in all batches and a vari Voc < 2 mV
show, that the used base material in the paste, replacing the silver particles, does not influence the lifetime of the
silicon material of the solar cell. Electroluminescence images confirm this result.
Fig. 2: