INVESTIGATION OF MATERIAL-INDUCED-SHUNTS IN BLOCK-CAST MULTICRYSTALLINE SILICON SOLAR CELLS CAUSED BY SiC PRECIPITATE FILAMENTS

摘要

In this work the 3-dimentional structure of four types of precipitates found in block-cast shunted silicon solar cells has been elucidated. Some of these precipitates led to strong ohmic shunts. The dominant type of shunt is caused by SiC filaments 1-3 μm in diameter crossing the cells. These filaments are incorporated in large-angle grain boundaries. The other types of precipitates seem to be not so dangerous. None of these precipitates have been found in good quality block-cast silicon solar cells. The SiC precipitates are predominantly appearing in the upper part of silicon blocks owing to the segregation effect. The SEM investigation support our hypothesis that not the SiC precipitates themselves represent the conducting channels but ring-shaped inversion channels around them. The positive charge causing this inversion could be due to nitrogen donor ions in the SiC, which have lost their electrons into the p-type silicon.