Characterization of silicon polycrystalline solar cells at cryogenic temperatures with ion beam-induced charge

We present a spatial analysis of biased polycrystalline silicon solar cell samples at cryogenic temperatures by the ion beam-induced charge technique. Performing the measurements at cryogenic temperatures leads to freezing out of deep trapping centers, a reduction of the specimen’s capacitance, an increase in the mobility of carriers, and an improvement in the signal to noise ratio and charge collection efficiency. At this low temperature, it permits a higher sensitivity analysis when compared to room temperature measurements, which are limited to zero bias due to leakage current that occurs via surface carrier trapping and detrapping along the grain boundaries. As a result we find the images are significantly more sensitive to subtle differences in charge collection efficiency arising from intra-grain defects.