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Characterizing local contact resistances of interdigitated back contact silicon solar cells
: Padilla, M.; Michl, B.; Reichel, C.; Hagedorn, N.; Kluska, S.; Haag, S.; Keding, R.; Fell, A.; Kasemann, M.; Warta, W.; Schubert, M.C.
Next generation high efficiency interdigitated back contact (IBC) silicon solar cells are often designed with complex doping and contacting structures that are sensitive to series resistance induced losses. Particularly local contact resistance problems present a major fill factor loss in industrially feasible solar cell designs. In this work, we use advanced two dimensional device simulations to understand the impact of globally and locally deteriorated electron and hole contacts on a typical IBC design. For a set of examples, the effect of an increased contact resistance on the global current voltage characteristic is compared to the signature of a simulated local series resistance image using luminescence imaging. Consistent interpretations and quantitative agreement between global and local analysis are shown. We find that the local series resistance of IBC cells react identically for globally altered electron and hole contact resistances. However, locally deteriorated electron and hole contact resistances do not impact fill factor losses identically. Together with qualitative interpretation of luminescence images, these findings present valuable information for IBC cell manufacturers for understanding their cell design's sensitivity to local contact resistance or broken finger problems on fill factor and short-circuit current.