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Grain control in directional solidification of photovoltaic silicon

Authors
Journal
Journal of Crystal Growth
0022-0248
Publisher
Elsevier
Publication Date
Volume
360
Identifiers
DOI: 10.1016/j.jcrysgro.2012.01.007
Keywords
  • A1. Directional Solidification
  • A3. Grain Growth
  • B2. Semiconducting Materials
  • B2. Semiconducting Silicon
  • B3. Solar Cells

Abstract

Abstract Directional solidification (DS) has become the major process for growing multi-crystalline silicon (mc-Si) for solar cells in the photovoltaic industry. The control of grains, as well as the grain boundaries, is particularly important to the crystal quality, and thus the solar cell efficiency. In this paper, we review the progress in the grain control of DS mc-Si from lab-scale to industrial-scale experiments. The control of the growth front was found effective in improving the grain size, but the grain size was found decreased with growth due to the sub-grain formation. With a better control of nucleation and grain competition by increasing the undercooling through enhanced uniform or spot cooling, grains with more Σ3 or twin boundaries were obtained. As the grain size increased with height, the growth of dislocations was found much slower than that without grain growth. The conversion efficiency of the solar cells fabricated from the wafers with grain control was significantly improved. Moreover, the seeded growth was also discussed.

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