Forward- and reverse-bias tunneling effects in N+P silicon solar cells

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Excess currents due to field-assisted tunneling in both forward and reverse bias directions have been observed in n+-p silicon solar cells. These currents arise from the effect of conducting paths produced in the depletion layer by n+ diffusion and cell processing. Forward-bias data indicate a small potential barrier with height ∼0.04 eV at the n+ end of conducting paths. Under reverse bias, excess tunneling currents involve a potential barrier at the p end of the conducting paths, the longer paths being associated with smaller barrier heights and dominating at the lower temperatures. Low-reverse-bias data give energy levels of ∼0.11 eV for lower temperatures (253–293 K) and ∼0.35 eV for higher temperatures (293–380 K). A model is suggested to explain the results.