成果報告書詳細
管理番号20110000000655
タイトル*平成22年度中間年報 新エネルギー技術研究開発 革新的太陽光発電技術研究開発(革新型太陽電池国際研究拠点整備事業)高度秩序構造を有する薄膜多接合太陽電池の研究開発(ヘテロ接合デバイス化~低ダメージ成膜)
公開日2011/8/25
報告書年度2010 - 2010
委託先名京セラ株式会社
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 [平成22年度末(中間目標)] ボトムセル:バンドギャップ0.9eV以下のシリコンゲルマニウム、シリコンゲルマニウムスズなどの単結晶基板を用いたヘテロ接合太陽電池で、開放電圧0.3V以上、変換効率8%以上を得る。他のサブテーマで開発する要素セルと組み合わせることにより、メカニカルスタック3接合太陽電池で変換効率20%以上。 (1)研究開発の方針について シリコンベースの太陽電池で変換効率40%超を実現するため、約1.8eVのワイドギャップセル、約1.1eVのミドルセル、および約0.7eVのボトムセルをメカニカルスタックにより直列接続する方式を検討されており、本テーマではシリコンゲルマニウム系材料を用いたボトムセルの研究開発を行う。
英文要約Title: Multi-Junction Thin Film Solar Cells with Highly Ordered Structure. Low Damage Formation of Hetero-Junction on Triple Junction Thin Film Silicon Solar Cells. (FY2008-FY2012)FY2010 Annual Report.
[Objective in FY 2010] We aim to achieve conversion efficiency (eta) = 8.0 % and open circuit voltage (Voc) >= 0.3 V on the bottom cell in triple junction thin film solar cell with mono-crystalline wafer of low bandgap (Eg) materials (Eg <= 0.9 eV) such as silicon-germanium (SiGe) and silicon-germanium-tin (SiGeSn). Our final target is eta >= 20.0 % as a triple junction solar cell by introducing this bottom cell. [1. Our Policy] In this project, we focus on the bottom cells. Ge has narrow bandgap and its power drops above 60 degree C due to its increase of reverse saturated current. To avoid this, we need to improve the cell voltage and temperature coefficient by forming a heterojunction. In order to form excellent heterojunctions on the bottom cells, it is necessary to improve minority-carrier lifetime (tau) by cleaning the surface of the substrates which become light-absorption layers and to perform low damage formation of thin films to keep or improve the characteristics of the light-absorption layer next. For this purpose, we used the Si materials whose physical properties are well known, and evaluated various processes as follows to clean the surface of the substrates and to perform low damage formation. [2. Results] (1. Evaluation of surface-cleaning process of substrates) A hot-water dipping process was carried out and evaluated to Si Czochralski (CZ) (111) substrates removed a natural oxide film. By adjusting the processing condition, we found that the tau after the process was more than 10 times larger than that before the process. Recombination velocity (S) which is evaluated from this result was decreased, and it was almost equals to the value of a sample which is applied quinhydrone/methanol (Q/M) chemical passivation. (2. Evaluation of interface on heterojunction by low damage formation) Low damage formation was carried out on the samples with the surface-cleaning process, and cross-sectional transmission electron microscope (TEM) observation and element analysis was performed. We found there was difference of crystallinity and some elements detected near the interface between the samples with a hot-water dipping process and those with normal treatment. (3. Application of a hot-water dipping process to fabrication of heterojunction solar cells) Heterojunction solar cells were fabricated by using the samples to which the surface-cleaning process is applied. The specifications of them are (1) one-sided heterojunction, (2) no back surface field (BSF), and (3) no texture on the surface. Current obstruction which is caused by surface cleaning process is not observed. The eta of p-type germanium heterojunction solar cells, on the other hand, is very low. The strategy of the process for improvement of eta is being investigated.
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