Reliability Degradation Indicators being Observed on Terrestrial Silicon Solar Cells

Results of a program to investigate the reliability characteristics of unencapsulated low-cost terrestrial solar cells using accelerated stress testing are presented. A total of seven types of cells were investigated. Results of extended (~ 1 year) bias-temperature stress testing of four cell types were obtained. An additional three cell types, including cells fabricated using the advanced technologies of ribbon-grown silicon and polycrystalline silicon, were subjected to various combinations of bias, temperature cycling stress tests. The spectrum of tests used was based on previous years´ work, but differs from that used earlier. An electrical measurement procedure capable of distinguishing small changes in cell electrical parameters was used. Significant degradation was shown by some cell types in some stress tests. Other combinations of cell types and stress tests resulted in no detectable cell degradation. Analysis of the origins of the differences in degradation is continuing. Second quadrant characteristics of some cell types were also investigated in order to establish the electrical behavior of cells which may be exposed to this stress condition in modules deployed in the field.