Quasi-steady-state lifetime measurements on blocks: prediction of cell efficiency

One of the major obstacles for the worldwide development of the photovoltaic is the production costs. One way to lower costs is to reduce scraps step by step and to keep the quality under control. The industrial quality control needs to be automatic, fast, and without any sample preparation. Up to now, we do not have information on quality of blocks except lifetime measured by micro-wave photoconductance decay (MW-PCD). In a previous work, it has been demonstrated that a methodology exists to get calibrated quasi-steady-state photoconductance measurement on silicon blocks. This was demonstrated by measuring lifetime, Fe and trapping on multi-crystalline silicon blocks coming from the production line. The interest of lifetime measurement and Fe on blocks is to provide an immediate feedback to crystal growth and to optimize the yield of wafering into efficient solar cells. Measurements on 6 blocks coming from the production line are made and in this paper we present the correlation between the measurements made on blocks and on sliced wafers from it. The measurements are made on as-cut wafers and through the cell process (after POCL₃ diffusion and silicon nitride deposition). Cells are made with these wafers and the electrical results are presented.