成果報告書詳細
管理番号20120000001184
タイトル*平成23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2011 - 2011
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)

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 of 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 Cu2O 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) film can be obtained by a chemical bath deposition technique in basic aqueous solutions containing the nitrate, ammonia ion, and thiourea, and the bandgap energy was controlled from 2.7 to 3.7eV by adjusting the thiourea concentration. The Cu(InGa)Se2 sola cell with the 3.7-eV-bandgap Zn(O,S) layer prepared by the CBD process showed a conversion efficiency of 6.8% under AM1.5G illumination. And, the conversion efficiency could be enhanced to 13.7% with the open-circuit voltage of 0.64V, short-circuit current density of 33mAcm-2, and FF of 0.64 by a simple immersion of the CBD-Zn(O,S) layer into a diluted ammonia water. The structural characterization was carried out for the 20~100-nm-thick-Zn(O,S) films and references of ZnO and ZnS by recording the X-ray absorption spectrum in a synchrotron radiation facility (SPring 8). The thickness was controlled by adjusting the time of the ammonia water immersion. The radial distribution functions (RDFs) calculated by Fourier transformation of XAFS region of the spectra indicated the local structure around the absorption element. The Zn(O,S) films with the thickness below 50nm showed a 1st peak at radial distance of 1.5 and 2.0A, which originated from the nearest neighbor elements of oxygen and sulfur, and the intensity ratio of the two peaks changed depending on the thickness. The 100-nm-thick Zn(O,S) film showed only 1 peak at around 1.5A, and any peak could not be observed at radial distance over 2.5A, suggesting poor long range ordering in the atomic arrangement. The differential RDFs calculated among the 100- and 50-nm-thick-Zn(O,S) films indicated that the Zn(O,S) film prepared by the CBD possessed a layered structure of Zn(O,S) and Zn(OH)2 and that the upper Zn(OH)2 layer could be eliminated by the dissolution in the ammonia water, as speculated by the thermodynamic consideration. The FE-TEM observation showed the existence of the crystalline Zn(O,S) layer heteroepitaxially grown in the vicinity of the heterointerface to the CIGS layer.

The CBD film is prepared by hydrolysis of the metal cation released from the ammonia complex by reacting thiourea. We proposed two parameters of solution pH value and total ammonia ion concentration, based on thermodynamic calculation. The precipitation formation throughout the solution was suppressed under the condition of high pH and high NH3 concentration, and the thin homogeneous Zn(O,S) film deposited over entire the substrate surface.
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