Technical silicon for high-efficiency PV cells

The project proved that by focused control on the mix of certain impurities in the MG Si feedstock followed by focused gettering during cell processing, stable low cost MG Si based high efficiency cells could be mass produced at the same high level as for EG Si based cells. Several MG based modules were produced and proved homogeneity and repeatability.

Causes and defect structures for instabilities in MG Si cells by reverse voltage breakdown were found. The role of impurity complexes or clusters were systematically analysed. Unknown clusters distributed at micro boundaries were discovered. These vast numbers of clusters could be used for internal gettering. Some new complexes turned out to have a far more significant impact than the hitherto typically suspected impurities. For example whereas researchers typically have tried to reduce the midgap energy levels created by complex pairs of Fe-B, B-O, Cu-related defects, it was found by surprise that in the MG Si material S and Na are active electrically and found in large concentrations. The project has introduced new methodologies of detecting and differentiating high impact impurity complexes. Thus new MG Si based ultra high efficiency cell designs can be developed in the future.