Extraordinarily High Minority Charge Carrier Lifetime Observed in Crystalline Silicon

Recent progress in surface passivation technology and wafer pretreatment already resulted in significant improvements in the achievable minority charge carrier lifetime of crystalline silicon. Herein, this is further exemplified by studying the lifetime on lowly doped crystalline silicon wafers passivated by poly-Si. To ensure credible lifetime measurements multiple measurement techniques are compared and good agreement between the investigated approaches is found. The resulting lifetime curves are analyzed in detail and the main limitation is very likely caused by silicon bulk recombination-most likely due to impurities. This analysis indicates that even very low impurity concentrations can be a limiting factor at the extraordinary high level of charge carrier lifetime observed in this study. Despite these limitations, lifetimes of 0.18 s on p-type and 0.5 s on n-type crystalline silicon wafers are measured, which to our knowledge exceed previously reported lifetimes. In both cases, these measured lifetimes correspond to an effective minority charge carrier diffusion length of ≈2.5 cm.