Floating cast method to realize high-quality Si bulk multicrystals for solar cells

We report on proof-of-concept experiments to demonstrate the advantages of "floating cast method" as a growth method to realize high-quality Si bulk multicrystals for solar cells. The fundamental concept is to use the top center of the melt as the nucleation site and to avoid contact between the crystal and the inner wall of the crucible during crystal growth. In contrast to the conventional casting method to start with inhomogeneous nucleation at the bottom of the crucible, the size of crystal grains is expected to become larger by limiting the number of nuclei. In addition, minimization of the contact of the crystal with the inner wall of the crucible is considered to result in low contamination of diffused impurities from the lining material as well as fewer defects by decreasing residual strain. These features are confirmed by comparing properties of crystals grown by the floating cast and the conventional methods. Furthermore, relative increase of the conversion efficiency of solar cells and the improvement of the material yield applicable to solar cells are presented, which certifies the advantage of the floating cast method. (C) 2008 Elsevier B.V. All rights reserved.