Bricks & Ingots

Photoluminescence characterisation of silicon bricks/ingots

In mass production, variations in silicon material quality cause significant variations in solar cell efficiencies. These fluctuations hinder efforts to make solar cells of higher efficiency and lower cost. Measurements, which are sensitive to these material fluctuations, can help identify their root cause and serve as an early warning. For this purpose, photoluminescence (PL) imaging of silicon bricks/ingots is being investigated. PL imaging of silicon bricks allows the in-line, spatially-resolved determination of bulk lifetime without any additional processing steps. Bulk lifetime is one of the key parameters affecting solar cell efficiency and it is generally not possible to measure after the bricks have been wafered. Therefore, PL imaging of silicon bricks presents an ideal opportunity to simply characterise the bulk lifetime and provide faster feedback to the silicon production process.

In this project, the PL imaging method for silicon bricks is being advanced in terms of accuracy and finding wider applications. The technique is applicable to all silicon bricks and sufficiently thick “slugs” without surface passivation. The technique can also be used to detect grain boundaries, dislocations, and the interstitial iron concentration in p-type material. Finally, large experiments comparing the bulk lifetime in silicon bricks with final solar cell efficiencies are of great interest, especially in collaboration with industrial partners.

  1. B. Mitchell, T. Trupke, J. W. Weber, and J. Nyhus, “Bulk minority carrier lifetimes and doping of silicon bricks from photoluminescence intensity ratios,” J. Appl. Phys., vol. 109, no. 8, p. 083111, 2011.
  2. B. Mitchell, D. Macdonald, J. Schon, J. W. Weber, H. Wagner, and T. Trupke, “Imaging As-Grown Interstitial Iron Concentration on Boron-Doped Silicon Bricks via Spectral Photoluminescence,” IEEE J. Photovoltaics, vol. 4, no. 5, pp. 1185–1196, Sep. 2014.
  3. D. Chung, B. Mitchell, M. Goodarzi, C. Sun, D. Macdonald, and T. Trupke, “Bulk Lifetimes up to 20 ms Measured on Unpassivated Silicon Discs Using Photoluminescence Imaging,” IEEE J. Photovoltaics, vol. 7, no. 2, pp. 444–449, Mar. 2017.
  4. B. Mitchell, D. Chung, Q. He, H. Zhang, Z. Xiong, P. P. Altermatt, P. Geelan-Small, and T. Trupke, “PERC Solar Cell Performance Predictions From Multicrystalline Silicon Ingot Metrology Data,” IEEE J. Photovoltaics, vol. 7, no. 6, pp. 1619–1626, Nov. 2017.
  5. D. Chung, B. Mitchell, M. K. Juhl, M. Abbott, and T. Trupke, “Lifetime Imaging on Silicon Bricks Using the Ratio of Photoluminescence Images With Different Excitation Wavelengths,” IEEE J. Photovoltaics, vol. 8, no. 4, pp. 943–951, Jul. 2018.

This work is funded through the Australian Renewable Energy Agency under projects RND009