We examine the carrier lifetime evolution of block-cast multicrystalline silicon (mc-Si) wafers under illumination (100 mW/cm2) at elevated temperature (75°C). Samples are treated with different process steps typically applied in industrial solar cell production. We observe a pronounced degradation in lifetime after rapid thermal annealing (RTA) at 900°C. However, we detect only a weak lifetime instability in mc-Si wafers which are RTA-treated at 650°C. After completion of the degradation, the lifetime is observed to recover and finally reaches carrier lifetimes comparable to the initial state. To explain the observed lifetime evolution, we suggest a defect model, where metal precipitates in the mc-Si bulk dissolve during the RTA treatment.

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We examine the light-induced carrier lifetime degradation and regeneration at elevated temperature in multicrystalline silicon (mc-Si) wafers of different thicknesses. The experimental results show that the thinner the wafer the less pronounced the degradation is and the faster the regeneration takes place. We interpret this result in the framework of a recently proposed defect model, where the lifetime regeneration is attributed to the diffusion of the recombination-active impurity to the wafer surfaces, where it is permanently trapped. Modeling the measured thickness-dependent lifetime evolutions enables us to determine the diffusion coefficient of the impurity to be in the range (5 AE 2) Â 10 À11 cm 2 s À1 at a temperature of 75 C.Comparing the diffusion coefficient extracted from our measurements with data published in the literature allows us to exclude most impurities.Despite the large uncertainties in the diffusion coefficient data reported in the literature, reasonable agreement is only obtained for nickel, cobalt, and hydrogen. One important practical implication of our study is that mc-Si wafers thinner than 120 μm do not suffer from pronounced light-induced lifetime degradation.