Quality Control of Czochralski Grown Silicon Wafers in Solar Cell Production Using Photoluminescence Imaging
Recent progress with photoluminescence (PL) imaging shows that applying pattern recognition techniques on the images of as-cut multicrystalline silicon (mc-Si) wafers allows a prediction of final solar cell parameters. Based on PL a reliable quality control for electrical parameters can thus be established for mc-Si wafers. High-efficiency solar cells are fabricated from Czochralski silicon (Cz-Si) wafers in most cases because of their high material quality. In this study, however, solar cells from Cz-Si suffered an efficiency loss of more than 4 % absolute due to a defect which appears as dark rings in PL images. In this paper we will show that the origin of this defect lies in oxygen precipitation during emitter diffusion. By using QSSPC-based lifetime measurements or PL-imaging, critical wafers can be identified and sorted out reliably at an early state of production and thus yield and average efficiency of production lines can be increased.