Defect mitigation in silicon

Crystalline silicon (c-Si) is the material of which a growing >85% of industrial solar cells are manufactured. The performance of c-Si devices has historically been limited by metallic impurities, especially iron, which can degrade solar-cell performance by several percent absolute. Complex cost and performance trade-offs govern solar-cell manufacturing, making impurity management a persistent challenge in PV manufacturing.

Innovations: The PVLab contributed to a body of literature that today assists iron mitigation during solar-cell manufacturing. Among our specific contributions, we developed and/or applied: (i) nanofocused X-ray mapping techniques to measure the distribution of precipitated iron in modern industrial c-Si materials[1]; (ii) simulation tools to predict the evolution of fast-diffusing iron impurities during solar-cell processing[2]; and (iii) novel annealing treatments to mitigate iron during solar-cell processing[3], resulting in yield, throughput, and performance enhancements at industrial partners[4]. Key challenges we faced include improving the detection limit of synchrotron techniques to measure iron in modern c-Si materials, which are orders of magnitude more pure than those made a decade ago. This work did not occur in a vacuum; we benefit from a worldwide network of collaborators who contribute complementary techniques, simulations, industry interactions, and perspectives[5].

[1] M.I. Bertoni et al., Energy & Environmental Science 4, 4252–4257 (2011)
[2] J. Hofstetter et al., Progress in Photovoltaics 19, 487–497 (2010)
[3] D.P. Fenning et al., Journal of Applied Physics 113, 214504 (2013)D.P. Fenning et al., Journal of Applied Physics 113, 044521 (2013)J. Hofstetter et al., Physica Status Solidi A 209, 1861-1865 (2012)
[4] D.M. Powell et al., Photovoltaics International 15, 91 (2012)
[5] J. Schön et al., IEEE Journal of Photovoltaics 3, 131-137 (2013)

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