成果報告書詳細
管理番号20110000000864
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 太陽電池用シリコンの革新的プロセス研究開発(シリカの直接還元プロセスの開発)
公開日2011/6/29
報告書年度2010 - 2010
委託先名国立大学法人弘前大学
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.緒言
太陽光エネルギーは、世界の一次エネルギーの多くを賄いうる可能性を有しており、化石燃料代替としてのクリーンエネルギーのひとつとして期待されている。表1 に示されるように太陽電池素材としては、結晶Si 系、CdTe 系、高分子系等があるが、Si(シリコン)が主でこれまでは半導体集積回路用の高純度(11N)シリコンのスクラップが用いられてきた。
そこでのSi 高純度化に用いられるシーメンス法はシリコンを塩酸と反応させてトリクロロシラン(SiHCl3)と呼ばれる液体を得て、蒸留と精製により不純物を除去して高純度に精製したトリクロロシランと水素とを高温下で反応させて高純度シリコンを析出させる方法であるが、原理的にシリコンまで還元されるのは最大25%までであり、 残りの75%の副産物であるSiCl4 は処理が厄介で効率が悪いため、高コストであることが難点である。今後、太陽電池の世界的な需要増大に対しては、ソーラーグレードシリコンSOG-Si(6N レベル)の大量かつ安価な供給が望まれるようになった。
その目標に対して、本研究では、砂漠等に大量に存在する珪砂(シリカ、SiO2)からのSOGSi精製への直接還元法プロセスを開発する。その素反応を以下に示す。
英文要約Title:Direct Reduction Process of Silica(SiO2) to SOG-Si-- High Temperature Heating Reduction Process of Mixture Silica and Carbon Composite Pellet -- (FY2010-FY2012) FY2010 Anuual Report
Supply of a large quantity of cheap solar grade silicon SOG-Si( 6N level) is required seriously. The Siemens method has been conventionally and widely used as the chemical refinement method to produce the high purity silicon (Si). However, in this study , we try to produce the purified SOG- Si from silica(SiO2) sand in the desert by using direct refining process from de-oxidation of pellets of SiO2 and carbon fine particles. Based on these progresses of refining SOG-Si in recent years, in this study, we examine the following research subjects as the beginning of the basic silica direct reduction process study in this year.
1. Improvement of the direct oxide-reduction process from SiO2 to Si device at the high temperature in laboratory experiments.
2. Making the powders mix material (i.e. pellet) of atomization carbon (carbon) and high purity silica (SiO2). Improvement of efficiency by the pre-treatment for the suitable pellet morphology.
3. Inspection of Si refinement and purity level of Si after oxide reduction from SiO2 by using high purified SiO2 and C fine particles under the oxide reduction by chemical reaction technique and discuss about the scientific and technical issues to produce the 6-N level SOG- Si with low cost and mass production process.
Results: We developed a combinatorial reducing furnace for silica, and fabricated silica and the pellet of the pre-purified SiO2 and carbon mixture and direct reduction from 1500 to 2000 degree Centigrade. Following results are obtained.
1) X-ray diffraction patterns of several products showed some peaks that look to be assigned to Si. It should be confirmed by another analysis, such as Raman spectra.
2) When the raw powder was packed to the crucible without escape path for the generated gas, accumulated gas at the bottom of the crucible ejects the raw powder from the crucible.
3) When the temperature is too high, the pellet (i.e. mixture of SiO2 with C particle) performs all sublimation.
4) In the case of lack of carbon, carbon die is apt to be eaten in itself.
5) Under high temperature process of de-oxidation at the high temperature, sublimation of SiO seems to begin at around the 1,400 degrees Celsius intensely. In addition, SiO seems to change in SiC by a reaction with carbon.
6) There is possibility that three consecutive reactions happened in a high temperature furnace. We have to consider the way to push the reaction toward purified Si formation while controlling the unexpected formation of SiO and SiC.
7) Present conditions of mass of pellet is too small to analysis because of small amount of Si product (~ 0.2 g) product. Tens of gram order mass is surely required for purity analysis, and the design improvement in a furnace will be needed in next stage program.
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