成果報告書詳細
管理番号20140000000667
タイトル*平成24年度中間年報 太陽エネルギー技術研究開発 太陽光発電システム次世代高性能技術の開発 極限シリコン結晶太陽電池の研究開発 (浮遊キャスト成長法による高品質Si 多結晶インゴット結晶成長技術)
公開日2015/2/19
報告書年度2012 - 2012
委託先名国立大学法人東北大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title:High Performance PV Generation System for the Future. R and D on Ultimate Wafer-based Si Solar Cells. (Growth technology of high-quality Si multicrystal ingots using the Floating Cast Method) (FY2010-FY2014) FY2012 Annual Report

We attempted to scale up the floating cast method to grow high-quality multicrystalline Si (mc-Si) ingot.The concept of the floating cast method is to control the crystal growth and microstructures by utilizing dendrite crystals from the top of Si melt in a crucible with minimizing the contact of the ingot with the inner wall until the melt is entirely solidified. We can expect that the grain size will become larger by limiting the number of nucleation sites at the top center of the Si melt. In addition, grain boundary character can be controlled to suppress generation of dislocations by controlling the contact angle between adjacent dendrite crystals at the initial stage of the crystal growth. Incorporation of impurities and generation of dislocations could be suppressed due to reduction of external stress during solidification.In order to reduce the contact of the ingot with the bottom of the crucible, we propose to use designed double crucibles to avoid the strong contact of the ingot with the bottom of the crucible at the final stage of the solidification, which would generate dislocations. This effort leads to spontaneous removal of the residual melt from the inner crucible to outer one, leading to the reduction of density of crystal defects (e.g. dislocations and sub-grain boundaries). In fact, we could successfully utilize the specially designed crucibles for the growth of a small-scale ingot. The results suggest that the floating cast method combined with specially designed double crucibles is feasible, which could be implemented to realize high-quality mc-Si ingot for practical size (156 mm ×156 mm) wafers. Therefore, we modified a large-scale furnace to permit to grow an ingot for practical size (156 mm × 156 mm) wafers so that we could realize a temperature distribution, which is suitable for the floating cast method. An appropriate cooling lead to the appearance of faceted dendrite crystals on the upper surface and the ingot contains a few large crystal grains originating from the dendrite crystals. In addition, generation of dislocations at the bottom could be suppressed owing to the utilization of the double crucible. Further improvements of the floating cast method are underway to reduce impurities from atmosphere.
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