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Keywords:

  • inspection;
  • cracks;
  • luminescence;
  • wafers;
  • cells

ABSTRACT

We present a measurement technique that we call ‘edge-light’, which allows a very sensitive detection of cracks in solar wafers and cells. For polycrystalline material, we found to be able to detect much smaller cracks than possible with conventional equipment. The technique is based on dark-field illumination with the illuminating light entering the wafer (or the cell) from the edges and being kept inside the wafer by total internal reflection. As detector, an infrared line-scan camera is used, giving high resolution images. In this configuration, even small cracks appear with high contrast, whereas the grain structure is not visible. In the same setup, photoluminescence or electroluminescence can be recorded in the same run in order to gain information on electronic properties. For the case of photoluminescence, only the scan line needs to be irradiated by the optical excitation source. Consequently, the necessary optical power can be lower and/or exposure times can be shorter. The combination of several measurement channels (crack detection, luminescence) with different light/excitation sources and a single camera is achieved by a special application software for an field programmable gate array (FPGA) frame grabber. The integration of the two measurements principles in a single setup allows simultaneous determination of mechanical stability and electronic quality properties. The setup was proven to work under inline conditions. Copyright © 2012 John Wiley & Sons, Ltd.