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Light and elevated temperature induced degradation (LeTID) affects significantly the performance of multicrystalline (mc) Si PERC solar cells, and underlying mechanisms of LeTID are still unknown. In this work LeTID and following regeneration of an industrial mc-Si PERC solar cell is compared to differently processed minority charge carrier lifetime samples under illumination (1 sun) and elevated temperature (75°C). LeTID on cell level reveals the same kinetics compared to lifetime samples. Varying the processing sequence has a significant effect on LeTID of lifetime samples. Ungettered samples with fired SiN x :H surface passivation show a very strong LeTID and regeneration effect, with degradation kinetics being similar for all wafer areas irrespective of initial material quality. In contrast, regeneration sets in earlier in good quality areas. Differently gettered samples are less sensitive to LeTID, while overall degradation and regeneration behaviour is strongly influenced by applied gettering sequences. Al-gettered samples show a more pronounced degradation effect than P-gettered samples, leading to the assumption that P-gettering is more effective in the reduction of LeTID sensitive defects. A model is presented, describing LeTID in boron as well as gallium doped mc-Si being based on impurities that can be gettered and redistributed during high temperature steps.

The efficacy of higher-temperature gettering processes in reducing precipitated iron concentrations is assessed by synchrotron-based micro-X-ray fluorescence. By measuring the same grain boundary before and after phosphorus diffusion in a set of wafers from adjacent ingot heights, the reduction in size of individual precipitates is measured as a function of gettering temperature in samples from the top of an ingot intentionally contaminated with iron in the melt. Compared to a baseline 820 C phosphorus diffusion, 870 C and 920 C diffusions result in a larger reduction in iron-silicide precipitate size. Minority carrier lifetimes measured on wafers from the same ingot heights processed with the same treatments show that the greater reduction in precipitated metals is associated with a strong increase in lifetime. In a sample contaminated with both copper and iron in the melt, significant iron gettering and complete dissolution of detectable copper precipitates is observed despite the higher total metal concentration. Finally, a homogenization pre-anneal in N 2 at 920 C followed by an 820 C phosphorus diffusion produces precipitate size reductions and lifetimes similar to an 870 C phosphorus diffusion without lowering the emitter sheet resistance. V C 2013 AIP Publishing LLC. [http://dx.

The root cause of light- and elevated temperature-induced degradation (LeTID) in multicrystalline silicon p-type passivated emitter and rear cell (PERC) devices is still unknown. Microwave-induced remote hydrogen plasma (MIRHP) is employed to vary the concentration of bulk hydrogen and to separate the effects of hydrogen and firing temperature in LeTID-affected wafers. We find that hydrogen is required for degradation to occur, and that samples fired prior to the introduction of hydrogen do not degrade. Importantly, samples with hydrogen that have not been fired do degrade, implying that the firing time-temperature profile does not cause LeTID. Together, these results suggest that the LeTID defect reaction consists of at least two reactants: hydrogen and one or more defects that can be separately modified by high-temperature firing. We assess the leading hypotheses for LeTID in the context of our new understanding of the necessary reactants.

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