成果報告書詳細
管理番号20120000001173
タイトル*平成23年度中間年報 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2013/10/31
報告書年度2011 - 2011
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
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) FY2011 Annual Report

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. Correlations between these characteristics and fabrication parameters and guiding principle for process-optimization are to be clarified.

(1) Characterization of electronic structure of Cd-free buffer and band alignment at interfaces between them and CIGS Considering that band gap energy of CBD-Zn(S, O, OH) and In(S, O, OH) are dominated by S/(S+O) ratio and OH-group concentration revealed in the last FY, dependences of conduction band minimum CBM on these composition and spatial profile of CBM in the buffers are investigated. CBM of ZnS and In2S3 simple sulfides are much higher or below that of CIGS, respectively. It causes a serious interface barrier or non-preferable type II conduction band alignment. For the OH-group poor buffers, partial substitution of oxygen for sulfur by 10 ~ 40 % leads an approach of CBM to that of CIGS. The improved conduction band alignment yields a rise of conversion efficiency above 13 %. The present study revealed the presence of cation concentration gradient along the depth direction of the as-grown buffers. Surface. CBM of OH-group rich surfaces of as-grown CBD-Zn(S, O, OH) exceeded that of CIGS more than 0.5 eV, which resulted in a formation of barrier against electron transport. It is also revealed that post-deposition treatments including chemical- or physical-etching and annealing above 200 - effectively reduce OH-group concentration as well as the height and thickness of the electronic barrier. These favorable modifications cause a remarkable rise of efficiency above 16 %. The studies in this FY clarified anion concentrations of the Cd-free buffers are keys of high efficiency, which is accomplished by optimization of both CBD and post-deposition processes.

(2) Characterization of built-in potential Vb of grain boundaries of the buffers CBD-Zn(S, O, OH) layers consist of sub-micron size agglomerated grains of fine primary particles. Kelvin probe force microscopy has revealed that Vb at boundaries between the primary particles is in negligible level for transport phenomena at ambient temperature. Though Vb between the agglomerated grains is fairly high above 100 mV, it should hardly affect the carrier transport along the layer-stacking direction since thickness of the buffer is much smaller than the grain-size. It is, consequently, clarified that the boundaries in Zn(S, O, OH) should be electrically inactive and non-harmful to cell-performances.
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