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Study of the zig-zag grain boundary in multicrystalline silicon
|A. Nadri , Thierry Duffar , Y. Duterrail-Couvat , S. Epure|
SIMaP EPM, CNRS UJF, BP 75, Saint Martin d'Heres cedex 38402, France
|There are numerous Grain boundaries (GB) in photovoltaic multicrystalline silicon, with the drawback of decreasing the solar cell efficiency. While those GB are generally straight or bended, some of them have a zig-zag shape. We developed a theoretical model  in order to describe the origin and development of GB during the solidification of the silicon ingot. The theoretical model developed in  describes the origin and development of GB during the solidification of the silicon ingot. One of the conclusions of the model is that  facets may exist at the liquid-grain-grain triple line during growth. Zig-zag grains are predicted to occur when the facet of one grain becomes parallel or perpendicular to the solid-liquid interface. In such cases, another facet of the  family appears on this grain, replacing the wrongly oriented one. A numerical simulation (performed with ANSYS Fluent) of heat transfer in the vicinity of the faceted groove shows that the new facet is likely to subsist for some time. Consequently the GB orientation changes and the new facet becomes wrongly oriented, then shifting to the initial one.
The objective of this work is to validate experimentally this theoretical expectation. In this purpose, appropriate zones in Si ingots were selected, cut and polished at places showing zig-zag GB. These samples were analyzed by EBSD with a SEM in order to find the crystallographic orientation of the two grains forming the GB. The orientation of the  planes in both grains are compared and the possibility that one of them is perpendicular or parallel to the S/L interface is discussed. It appears that the experimental observations are in agreement with the model. “The solid-solid-liquid triple line and its effect on the grain structure of multi-crystalline photovoltaic silicon” T. Duffar and A. Nadri, C. R. Ac. Sci. Ser. Physique, 14 (2013) 185–191.
Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 7, by Thierry Duffar
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17
Submitted: 2013-04-12 18:50 Revised: 2013-07-23 16:31