成果報告書詳細
管理番号20130000000115
タイトル*平成24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 CZTS薄膜太陽電池の高効率化技術の研究開発 -機能層・セル内界面の電子構造評価・最適化に関する研究開発-
公開日2013/6/25
報告書年度2012 - 2012
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: Development of high-efficiency CZTS solar cells and submodules (FY2012-FY2013) FY2012 Annual Report

1. Objectives: Electronic structures of buffer and absorber layers and interfaces and electronic activity of grain boundaries are to be investigated for developing key technologies for higher conversion efficiency in CZTS based cells. Correlations between these characteristics and fabrication parameters and guiding principle for process-optimization are to be clarified.
2. For FY 2012 (1) Establishment of Standard Data of Electronic Structure of CZTS
Electronic structure of cleaned surface of stoichiometric polycrystalline CZTS has been analyzed by means of UPS and IPES. It shows band gap energy about 1.4 eV, ideal for the absorption of sunlight, with valence band maximum VBM of -0.5 eV and conduction band minimum CBM of 0.9 eV.
(2) Characterization of surface nature of CZTS absorber layer
Surface of CZTS layers fabricated by vacuum deposition and sulfurization is rather chemically active. Zn and Sn are selectively react and forms oxides and hydroxides, which results in expansion of band gap energy and rise of CBM above 1.2 eV. The reacted regions are effectively removed by chemical treatments such as H2O-rinse and NH3-etching. Dependence of surface sensitivity of analysis condition revealed that the treated surfaces region with thickness around 10 nm should have significantly Cu-poor composition. Energy separations between VBM and core-levels of Zn and Sn are independent of the surface treatment, whereas that non-negligible variation between VBM and Cu-core level is observed. These results indicate that the Zn and Sn should be major cations of intrinsic surface of the CZTS layer. In spite of the compositional difference, electronic structure of the treated surface shows band gap energy about 1.45 eV with VBM of -0.55 eV and CBM of 0.9 eV. The similar electronic structure to the stoichiometric one indicates that the Cu-poor surface region may have Kesterite-related structure. The effects of surface treatment and compositional characteristics of CZTS layer should be considered for optimizing interface electronic structure.
(3) Development of in-situ analysis of buffer/CZTS interfaces
Molecular beam epitaxy and multi-target sputtering systems by which various buffer layers including CdS, Zn(O, S), (Zn, Mg)O and In(O, S) are combined with PES/IPES system. By utilizing it, in-situ analysis of interface induced band bending and band offset has been started.
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