Photoluminescence analysis of intra-grain defects in cast-grown polycrystalline silicon wafers

Effects of intra-grain defects in cast polycrystalline silicon (poly-Si) wafers on the solar cell performance were investigated by photoluminiscence (PL) spectroscopy and mapping at room temperature. We confirmed that the crystallinity of the longer diffusion length region of the poly-Si is almost the same as that of the single crystalline Si. For the PL macroscopic mapping, low PL intensity regions correspond to short diffusion length regions. In short diffusion length regions, plenty of dark lines and spots were observed by PL microscopic mapping, while, in contrast, longer diffusion length regions have few of them. These findings showed clearly that dark lines and spots of the PL mapping relate to defects degrading the cell performance. We also found that structures of defects depend on the fabrication process.