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成果報告書詳細
管理番号20160000000266
タイトル*平成27年度中間年報 高性能・高信頼性太陽光発電の発電コスト低減技術開発 太陽電池セル、モジュールの共通基盤技術開発 CIS太陽電池高性能化技術の研究開発(界面制御によるカルコゲナイド系薄膜太陽電池の高効率化)
公開日2017/4/13
報告書年度2015 - 2015
委託先名国立大学法人東京工業大学
プロジェクト番号P15003
部署名新エネルギー部
和文要約
英文要約Title: High-Efficiency Chalcopyrite Thin-Film Solar Cells with Controlled and Modified Interfaces (FY2015 - FY2019)FY2015 Annual Report, Tokyo Institute of Technology

In order to realize high-efficiency Cu(InGa)Se2 (CIGS) thin-film solar cells, the development of device technology and analysis of device modeling are quite important. In our group, we focus on the control of surface and interface properties, because CIGS thin-film solar cells have many heterointerfaces, and these interface properties, such as recombination rate, determine the overall cell performances. (1) Control of Surface and Interface Properties : For improvement of CIGS solar cell performances we inserted Cu(InGa)3Se5 (Cu-poor) layer at the CdS/CIGS interface. The Cu-poor layer has a wider bandgap than CIGS, and it forms the positive valance band offset (dEv). This dEv repels holes from the CdS/CIGS interface resulting in the reduction of the interface recombination. The Cu-poor layer was grown by a co-evaporation method. It was found from experiments that a growth interruption (1 min) or a low-temperature growth (380 oC) was important to enhance the cell performance, since the intermixing of atoms occurred during the growth of the Cu-poor layer at a high temperature (550 oC) without growth interruption. The efficiency of 15 - 16% without the Cu-poor layer was improved up to 17 - 18% with the Cu-poor layer. (2) Reformation of Surface and Interface Properties : We have developed a thiourea surface treatment, and it was found that the treatment was effective to enhance the Cu2ZnSn(S,Se)4 solar cell efficiencies. In this project, we applied the method to CIGS and tried to improve the cell efficiency. The efficiencies of CIGS solar cells without Cu-poor layer were ranging from 17% to 18%, and they were slightly improved by the surface treatment. Furthermore, the efficiencies around 18% were obtained by using a Cu-poor interface layer, and the highest efficiency of 18.5% was achieve by the combination of the insertion of the Cu-poor layer and the thiourea surface treatment. (3) Control of Rear-Surface Properties : The bandgap of Si can’t be altered, and it has a low absorption coefficient and long diffusion length. Thus the efficiency of Si solar cells can be enhanced by the BSF (Back Surface Field) and passivation techniques. On the other hand, the bandgap of CIGS can be controlled by changing the Ga composition, and it has a high absorption coefficient and short diffusion length. Therefore, it should be clarified whether the same techniques, which improve the Si solar cell efficiency, are applicable to the CIGS solar cell or not. Based on this motivation we carried out device simulations, and it was found that the band profiling was as effective as the BSF and passivation techniques to boost the CIGS solar cell performance. This observation is quite import, since the bandgap is easily controlled for CIGS material. However, the development of a BSF structure and a passivation layer is hard to conduct for CIGS solar cells.
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