Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Engineering metal-impurity nanodefects for low-cost solar cells

Abstract

As the demand for high-quality solar-cell feedstock exceeds supply and drives prices upwards, cheaper but dirtier alternative feedstock materials are being developed1,2,3. Successful use of these alternative feedstocks requires that one rigorously control the deleterious effects of the more abundant metallic impurities. In this study, we demonstrate how metal nanodefect engineering can be used to reduce the electrical activity of metallic impurities, resulting in dramatic enhancements of performance even in heavily contaminated solar-cell material. Highly sensitive synchrotron-based measurements4,5 directly confirm that the spatial and size distributions of metal nanodefects regulate the minority-carrier diffusion length, a key parameter for determining the actual performance of solar-cell devices. By engineering the distributions of metal-impurity nanodefects in a controlled fashion, the minority-carrier diffusion length can be increased by up to a factor of four, indicating that the use of lower-quality feedstocks with proper controls may be a viable alternative to producing cost-effective solar cells.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type

from$1.95

to$39.95

Prices may be subject to local taxes which are calculated during checkout

Figure 1: The different types of metal defect in commercial solar-cell material.
Figure 2: Metal defect distributions in commercial and next-generation solar-cell materials.
Figure 3: Effect of the distribution of metal defects on material performance.

Similar content being viewed by others

References

  1. Woditsch, P. & Koch, W. Solar grade silicon feedstock supply for PV industry. Solar Energy Mater. Solar Cells 72, 11–26 (2002).

    Article  Google Scholar 

  2. Yuge, N. et al. Purification of metallurgical-grade silicon up to solar grade. Prog. Photovolt. Res. Appl. 9, 203–209 (2001).

    Article  Google Scholar 

  3. Khattak, C. P., Joyce, D. B. & Schmid, F. A simple process to remove boron from metallurgical grade silicon. Solar Energy Mater. Solar Cells 74, 77–89 (2002).

    Article  Google Scholar 

  4. Yun, W. et al. Nanometer focusing of hard X-rays by phase zone plates. Rev. Sci. Instrum. 70, 2238–2241 (1999).

    Article  Google Scholar 

  5. Cai, Z. et al. Performance of a high-resolution X-ray microprobe at the advanced photon source. AIP Conf. Proc. 521, 31–34 (2000).

    Article  Google Scholar 

  6. Davis, J. R. et al. Impurities in silicon solar cells. IEEE Trans. Electron Dev. 27, 677–687 (1980).

    Article  Google Scholar 

  7. Pizzini, S., Bigoni, L., Beghi, M. & Chemelli, C. On the effect of impurities on the photovoltaic behavior of solar grade silicon. II. Influence of titanium, vanadium, chromium, iron, and zirconium on photovoltaic behavior of polycrystalline solar cells. J. Electrochem. Soc. 133, 2363–2373 (1986).

    Article  Google Scholar 

  8. Istratov, A. A., Hieslmair, H. & Weber, E. R. Iron contamination in silicon technology. Appl. Phys. A 70, 489–534 (2000).

    Article  Google Scholar 

  9. Kittler, M. & Seifert, W. Estimation of the upper limit of the minority-carrier diffusion length in multicrystalline silicon: Limitation of the action of gettering an passivation of dislocations. Solid State Phenom. 95–96, 197–204 (2004).

    Google Scholar 

  10. Plekhanov, P. S., Gafiteanu, R., Gosele, U. M. & Tan, T. Y. Modeling of gettering of precipitated impurities from Si for carrier lifetime improvement in solar cell applications. J. Appl. Phys. 86, 2453–2458 (1999).

    Article  Google Scholar 

  11. Myers, S. M., Seibt, M. & Schröter, W. Mechanisms of transition metal gettering in silicon. J. Appl. Phys. 88, 3795–3819 (2000).

    Article  Google Scholar 

  12. Dorward, R. C. & Kirkaldy, J. S. Effect of grain-boundaries on the solubility of copper in silicon. J. Mater. Sci. 3, 502–506 (1968).

    Article  Google Scholar 

  13. Istratov, A. A., Huber, W. & Weber, E. R. Experimental evidence for the presence of segregation and relaxation gettering of iron in polysilicon layers. Appl. Phys. Lett. 85, 4472–4474 (2004).

    Article  Google Scholar 

  14. Green, M. A., Emery, K., King, D. L., Igari, S. & Warta, W. Solar cell efficiency tables (version 24). Prog. Photovolt. Res. Appl. 12, 365–372 (2004).

    Article  Google Scholar 

  15. Macdonald, D., Cuevas, A., Kinomura, A. & Nakano, Y. in Proc. 29th IEEE Photovoltaics Specialist Conf. 285 (IEEE, Piscataway, New Jersey, 2002).

    Google Scholar 

  16. McHugo, S. A. et al. Synchrotron-based impurity mapping. J. Cryst. Growth 210, 395–400 (2000).

    Article  Google Scholar 

  17. Manceau, A., Marcus, M. A. & Tamura, N. in Applications of Synchrotron Radiation in Low-temperature Geochemistry and Environmental Science Vol. 49 (ed. Sturchio, N. C.) 341–428 (Mineralogical Society of America, Washington DC, 2002).

    Book  Google Scholar 

  18. Buonassisi, T. et al. Quantifying the effect of metal-rich precipitates on minority carrier diffusion length in multicrystalline silicon using synchrotron-based spectrally-resolved X-ray beam induced current. Appl. Phys. Lett. 87, 044101 (2005).

    Article  Google Scholar 

  19. Schönecker, A., Geerligs, L. J. & Müller, A. Casting technologies for solar silicon wafers: block casting and ribbon-growth-on-substrate. Solid State Phenom. 95–96, 149–158 (2003).

    Article  Google Scholar 

  20. Hall, R. B. et al. Columnar grained polycrystalline solar cell substrate and improved method of manufacture. US Patent 6,111,191 (2000).

  21. Hiraga, T., Anderson, I. M. & Kohlstedt, D. L. Grain boundaries as reservoirs of incompatible elements in the Earth’s mantle. Nature 427, 699–703 (2004).

    Article  Google Scholar 

  22. Blavette, D., Cadel, E., Fraczkiewicz, A. & Menand, A. Three-dimensional atomic-scale imaging of impurity segregation to line defects. Science 286, 2317–2319 (1999).

    Article  Google Scholar 

  23. Ziegler, A. et al. Interface structure and atomic bonding characteristics in silicon nitride ceramics. Science 306, 1768–1770 (2004).

    Article  Google Scholar 

  24. Seager, C. H. Grain boundaries in polycrystalline silicon. Annu. Rev. Mater. Sci. 15, 271–302 (1985).

    Article  Google Scholar 

  25. Buonassisi, T. et al. Analysis of copper-rich precipitates in silicon: chemical state, gettering, and impact on multicrystalline silicon solar cell material. J. Appl. Phys. 97, 063503 (2005).

    Article  Google Scholar 

  26. Macdonald, D. H., Geerligs, L. J. & Azzizi, A. Iron detection in crystalline silicon by carrier lifetime measurements for arbitrary injection and doping. J. Appl. Phys. 95, 1021–1028 (2004).

    Article  Google Scholar 

  27. Lu, J., Wagener, M., Rozgonyi, G., Rand, J. & Jonczyk, R. Effects of grain boundary on impurity gettering and oxygen precipitation in polycrystalline sheet silicon. J. Appl. Phys. 94, 140–144 (2003).

    Article  Google Scholar 

Download references

Acknowledgements

Collaboration with M. Heuer, S. Fakra, M. D. Pickett, R. Jonczyk, T. F. Ciszek, K. O. Dijon, J. Isenberg, W. Warta, R. Schindler and G. Willeke is gratefully appreciated. This work was funded by National Renewable Energy Laboratory subcontract AAT-2-31605-03. Use of the Advanced Photon Source and of the Advanced Light Source is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract Numbers W-31-109-ENG-38 and DEAC03-76SF00098, respectively.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Andrei A. Istratov.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supporting supplementary material (PDF 61 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Buonassisi, T., Istratov, A., Marcus, M. et al. Engineering metal-impurity nanodefects for low-cost solar cells. Nature Mater 4, 676–679 (2005). https://doi.org/10.1038/nmat1457

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/nmat1457

This article is cited by

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing