Spatially resolved degradation and regeneration kinetics in mc-Si

Abstract

The strong degradation of multicrystalline (mc) Si material upon illumination at moderate temperatures (LeTID) is an issue that might hinder the application of PERC technology to mc-Si. Interestingly, a regeneration effect can also be observed under the same conditions, starting after several hundred hours at 75°C. Studies are mainly based on time resolved investigations, and some investigations also use spatially resolved measurement techniques. Visualization of the collected data is therefore challenging, but important for a better understanding of the underlying mechanisms.In this contribution we show that based on lifetime samples we can study the same effects as reported on solar cell level with a good spatial resolution. In ungettered samples originally good quality areas show a higher relative degradation as compared to originally poor quality areas. This behaviour changes completely for gettered samples. We also show that the regeneration process sets in earlier in good quality areas, which could be caused by the higher injection level present in these regions. The regeneration process therefore might be qualitatively similar to the known BO-related regeneration. A good point-to-point correlation of different sets of lifetime measurements allows to demonstrate the impact of local differences in material quality on degradation and regeneration behaviour.