Imaging of carrier lifetime variation during c-Si solar cell fabrication

The present work investigates the variation of minority carrier lifetime of silicon wafers after each processing step during the fabrication of silicon solar cells. Contactless photoconductance technique provides quantitative measure of the average lifetime. The spatial variation in the minority carrier lifetime is obtained by photoluminescence imaging. By combining these two techniques, we obtain the following significant results: i) edge isolation process degrades the lifetime near the wafer boundaries, ii) removal of phosphosilicate glass after POCl₃ diffusion degrades lifetime in the central region of the wafer, iii) high temperature processing steps e.g. emitter diffusion and contact firing result in improving / recovering the lifetime.