成果報告書詳細
管理番号20110000000334
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/フレキシブルCIGS太陽電池モジュールの高効率化研究(電子構造評価によるデバイス特性向上技術の開発)
公開日2011/7/28
報告書年度2010 - 2010
委託先名国立大学法人鹿児島大学
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 禁制帯幅1.4~1.5eVのワイドギャップCIGS太陽電池の高効率化に関して、NEDO未来技術により明らかとなった電子構造上の損失原因・その制御要素の解明をさらに進め、ワイドギャップCIGSと電子構造が整合するバッファ層用の物質・組成領域の探索・決定、粒界・欠陥・界面における要因を解明することで高効率化のための技術的指針を明確化・プロセスの中での解決方法の探索することで高効率化に貢献することを目的として、今年度は、1)高い変換効率・タンデム構造のトップセルとしての活用が期待されるワイドギャップCIGS光吸収層上で、適正な界面バンド接続を実現するためのバッファ層としてZn(S,O,OH)、In(S,O)系に注目し、主にアニオン濃度を変化させた一連のCBD-Zn(S,O,OH)層について、組成~結晶性~バンド端位置の関係を高分解能透過電子顕微鏡及び正・逆光電子分光法により評価し、OH基濃度、結晶化度によりバンド端位置、バンドギャップエネルギーが顕著な変化を示し、これらに先行研究で明らかにしたS/(S+O)比によるバンドギャップ湾曲を加えた3者がCBD-Zn(S,O,OH)の電子構造の支配要因であることを明らかにするとともに、CIGSと整合する電子構造が高S/(S+O)比、高結晶化度の層で得られること、その実現にCIGS上でのエピタキシャル成長が寄与することを明らかにした。
英文要約Title: The development of high performance flexible CIGS PV modules Development of key technologies for high-performance CIGS solar cells and modules based on characterization of their electronic structure (FY2010-FY2012) FY2010 Annual Report
1. Objectives: Electronic structures at interfaces and electronic activity of grain boundaries are to be investigated for developing key technologies for higher conversion efficiency in CIGS based flexible modules. The correlations between these characteristics and fabrication parameters and guiding principle for process-optimization are to be clarified.
2. For FY 2010
(1) Characterization of electronic structure of novel buffer-materials with electronic structure suitable to wide-gap CIGS In this FY, the research is focused on Cd-free oxysulfides with low electron affinity. Electronic structure of Zn(S, O, OH), In-(S, O) have been investigated.
(1)-1 Zn(S, O, OH); CBD-Zn(S, O, OH) layer grown on CIGS with various composition has been studied by PES/IPES. Their band structure are characterized with a significant band gap bowing as a function of S/(S+O) ratio and an expansion of band gap energy Eg up to 3.5 eV with OH content. A serious barrier against electron transport is formed by the expansion of Eg. It is, however, revealed that Eg and OH content can be reduced by promotion of crystallization. TEM images of cross sections of buffer/CIGS interfaces show that a region adjacent to CIGS has well-ordered structure. Post-annealing also improves it and reduces OH content. These results mean that S/(S+O), OH/(O+OH) ratios and crystallinity are dominant factors of electronic structure of CBD-Zn(S, O, OH). Control of S/(S+O) ratio within S-rich and promotion of crystallization by utilizing epitaxial effect on CIGS under-layer and by dehydration reaction by post-annealing are useful to realizing a proper conduction band offset at the interface.
(1)-2 In-(S, O); It is confirmed that conduction band minimum CBM of In2S3, is lower than that of CIGS by about 0.3 eV, which causes the unfavorable band alignment. Incorporation of oxygen results in an expansion of Eg and CBM, which is beneficial to form the favorable band alignment. The present study reveals that combination of ion etching and in-situ annealing at about 200C are a proper technique for studying depth-profile of electronic structure of In-(S, O)/CIGS junctions.
(2) Characterization of electronic activity of grain boundaries In photo-assisted UHV-Kelvin probe measurements, small portions of grain boundaries in Ga-rich CIGS exhibit positively charged features, which is not detected in In-rich specimens and unfavorable to carrier-separation. It indicates that control of GBs should be necessary for wide-gap CIGS-based cells.
3. Future Tasks Band alignments at novel buffer/CIGS interfaces are to be precisely investigated. Dependence of the electronic structure of the boundaries of wide-gap CIGS on growth conditions is to be clarified.
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