成果報告書詳細
管理番号20110000000790
タイトル*平成22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2011/6/23
報告書年度2010 - 2010
委託先名国立大学法人京都大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約和文要約等以下本編抜粋:1. 研究開発の内容及び成果等
今年度の成果のポイントを以下に記す。
【1】浮遊キャスト成長法によるインゴットの高品質化のための成長技術の基礎検討(京都大学) ・融液表面で核形成し、融液下部に向かって成長させることにより、極めて稠密にデンドライト結晶をインゴット結晶表面に形成することが出来る。このデンドライト結晶の下面から成長したインゴット結晶は、大きな結晶粒のみで構成される理想的な多結晶組織を有することを実証した。
・融液表面からの組織制御成長において、種結晶を利用すると、冷却速度等の制御により、単結晶組織でもデンドライト結晶からの多結晶組織でも自在に制御できることを示した。
研究開発の内容と成果をより具体的に以下に説明する。
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-FY2013) FY2010 Annual Report
Results of the research and developments
Basic research for the growth technology to obtain high-quality Si multicrystal ingots using "the Floating Cast Method" (Kyoto University)
This research was performed to make clear the basic crystal growth mechanism of "the Floating Cast Method", and realize Si ingots by controlling nucleation on the surface of Si melts and arrangement of dendrite crystals. The target at 2013 will be the realization of the diffusion length of about 200 μm using wafers (10 cm x 10 cm) cut from the ingots. The final goal at 2015 will be the establishment of technologies to obtain the diffusion length of about 500 μm using wafers (15.6 cm x 15.6 cm) cut from the high-quality ingots grown by the floating cast method, and the grasping of important factors to manufacture a pilot furnace.
As a fundamental research to reach the target at 2013, we found that Si ingots with ideal multicrystalline structures could be obtained using the floating cast method. In this method, nucleation occurred on the surface of Si melts and dendrite crystals densely grew on the surface. Si multicrystals grown under the dendrite crystals contained only large grains except for the edge of ingots. When we used Si seed crystals floating on the surface of Si melts for this method, we found that we could select single crystals or multicrystals by controlling the growth conditions such as cooling rate and so on.
The most important points to obtain high-quality Si multicrystals using crucibles are the purity, structure, crystal defect and stress control. We proposed the floating cast method mainly for the stress control on the view point of natural growth. In this method, nucleation occurs on the surface of Si melts, and bulk crystals naturally grow in Si melts from floating crystals on the surface of Si melts. Therefore, it is expected that the bulk crystals contains less stress even using crucibles. Dendrite crystals densely grew on the surface of Si melts without using seed crystals. Si ingots grown using a floating Si seed crystal had distinctive features of dendrite crystals which appeared from the seed. For example, when we used a round-shaped seed, dendrite crystals have a radial pattern. We could also arrange dendrite crystals in almost parallel to each other. Cross sections under the surface of the ingots had quite large grains grown from the seed or the dendrite crystals. Arrangement of dendrite crystals can be much easily controlled using seed crystals for this method.
For this method, the development of technologies to separate and carry out bulk crystals from remained Si melts is very important. We are now studying several methods to separate and carry out bulk crystals.
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