In-situ chemical analysis of molten photovoltaic silicon by Laser Induced Breakdown Spectroscopy

Laser induced breakdown spectroscopy (LIBS) has been used for the first time to determine in-situ the bulk chemical composition of a photovoltaic silicon melt. Our apparatus analyzes a freshly created and renewed surface inside the silicon melt which is truly representative of the melt composition in contrast to its surface. First, signal acquisition conditions are optimized to ensure that LIBS measurements overcome experimental fluctuations. Second, experimental parameters affecting plasma physics such as laser energy, bath temperature and bubbling gas are evaluated to maximize signal sensitivity and instrumental limits. Third, B, Al, Ti and Fe calibration curves are established. Selected conditions allow a reliable measurement which can be compared to classical ex-situ ICP-OES, with detection limit of few or even below ppmw. These results demonstrate the strong capabilities of LIBS for in-situ and in-line monitoring of metallurgical processes used in the photovoltaic industry.