成果報告書詳細
管理番号20130000000103
タイトル*平成24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(新規バッファ層の開発)
公開日2013/6/25
報告書年度2012 - 2012
委託先名国立大学法人豊橋技術科学大学
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: High performance PV generation system for the future. The development of high performance flexible CIGS PV modules (Development of Buffer Films and the Wet-Preparation Process)
(FY2010-2014) FY2012 Annual Report

The research and development program was to start in fiscal 2010 in order to fabricate Cu(InGa)Se2 (CIGS) photovoltaic devices with conversion efficiency over 16%. Toyohashi University of Technology (TUT) plays a role for developing new buffer layer and the wet preparation process, and two subjects of the optimization of structural characteristic of the buffer layers and development of technique to control the CBD reaction are carried out. Two types of oxides of ZnO and Cu-O are used as the buffer layer alternative to the CdS currently used as the buffer layer in the CIGS solar cell, because of the ionization energy of 3.8 and 3.3 eV, respectively.
The Zn(O,S,OH) layer is prepared by a chemical bath deposition (CBD) technique in basic aqueous solutions containing the nitrate, ammonia ion, and thiourea, and the local structures around the Zn atom in the Zn(O,S,OH) layer has been investigated based on radial distribution functions (RDFs) calculated from the X-ray absorption spectra taken in a synchrotron radiation facility (SPring 8). The local structure around the Zn atoms strongly depended on the substrate materials such as CIGS and soda-lime glass substrates, and the Zn(O,S,OH) layer prepared on the CIGS substrate had a layered structure of the upper Zn(OH)2 layer and lower highly crystallized Zn(O,S) layer near the CIGS substrate. The conversion efficiency of the CIGS solar cell with the Zn(O,S,OH) layer was improved from 6.8% to 13.7% by the simple immersion of the Zn(O,S,OH) layer into the diluted ammonia water solution to eliminate the upper Zn(OH)2 layer. The inverse photoelectron spectroscopy (iPES) measurements carried out in Kagoshima University indicated that the upper Zn(OH)2 layer generated the large conduction band offset (-Ec) around +1.0eV and the-Ec value was optimized to be about +0.5eV by the immersion. The conversion efficiency of 15.2% has been obtained for the CIGS solar cell with the Zn(O,S,OH) buffer layer by optimizing the preparation condition including the thiourea concentration. The Cu-doped Zn(O,S,OH) layer could be prepared from the Cu-Zn-NH3-solution, because that the potential-pH diagrams are similar for both the Zn-NH3-water and Cu-NH3-water systems. The bandgap energy continuously changed from 3.3 to 1.4eV depending on the solution composition.
The thermochemical simulation technique built in the CBD process for the Cu(O,S) layer preparation has been applied for the Zn(O,S,OH) deposition, and the condition for depositing homogenous Zn(O,S,OH) layer without the precipitation formation in the bulk solution has been found by optimizing the total NH3 concentration and pH value. And, the simulation technique is applied for the CBD-process used in industrial field for the CIGS solar cell fabrication to suppress the fabrication cost.
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