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Efficient carrier-selective p- and n-contacts for Si solar cells
The successful realization of carrier-selective contacts is a crucial prerequisite to approaching the theoretical efficiency limit of silicon solar cells. The herein proposed carrier-selective contacts resemble the polysilicon contacts, including a tunnel oxide, but make use of a wide bandgap semi-crystalline Si layer thereby forming a heterostructure with the crystalline silicon substrate. It will be shown that these tunnel oxide passivated contacts enable a low interface recombination, e.g. the electron contact achieved implied Voc (iVoc) of about 720 mV. On the other hand, the interface passivation quality provided by the hole contact was significantly lower (iVoc=680 mV) and it seems that its design is more challenging. The critical aspects which might explain the lower performance are addressed in this paper. On solar cell level good carrier selectivity was demonstrated which means that the passivated contacts effectively reduced minority carrier recombination and were transparent for majority carriers as well. The latter manifests itself in an external Voc of 694 mV and a FF of 81%. Raman spectroscopy revealed that the Si layer can partially contain crystalline Si phases and it will be demonstrated that this significantly improved the cell׳s blue response. In combination with the higher thermal stability these carrier-selective contacts could be a very appealing option for next generation high-efficiency silicon solar cells once the limitations for the p-contact are overcome.