成果報告書詳細
管理番号20120000000794
タイトル*平成23年度中間年報 新エネルギー技術研究開発/革新的太陽光発電技術研究開発(革新型太陽電池国際研究拠点整備事業)/ポストシリコン超高効率太陽電池の研究開発(自己組織化量子ドット)
公開日2012/11/28
報告書年度2011 - 2011
委託先名国立大学法人電気通信大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約和文要約等以下本編抜粋:
1.研究開発の内容及び成果等
本研究では、GaAs(001)基板上への面内超高密度InAs量子ドットの成長法を開発し、高い変換効率を有する中間バンド型太陽電池への応用について検討を進めている。平成23年度は主に以下の項目について検討した。
英文要約Title:R&D on innovative Solar Cells Post-silicon solar cells for ultra-high efficiencies (self-organization quantum dots) (FY2008-FY2012) FY2011 Annual Report
In the fourth year (2011) of this NEDO research project, our group of University of Electro-Communications developed in-plane ultrahigh density InAs quantum dots (QDs) and studied intermediate-band solar cells (IB-SC) using their QDs. The main results are described as follows. (1)In this project, fabrication of in-plane ultrahigh density QDs is one of important missions to realize the IB-SCs using the QDs. In this year, we successfully fabricated ultrahigh density InAs QDs with 5~6 ×1011 cm-2 on the GaAsSb/GaAs buffer layers and on the InAsSb wetting layers by molecular beam epitaxy (MBE). The coalescence and ripening processes of the QDs were effectively suppressed, as the results, in-plane ultrahigh density InAs QDs were obtained on the GaAs(001) substrates. (2)In order to analyze electronic states in the QDs, we measured temperature and excitation power dependences of photoluminescence (PL) properties of the in-plane ultrahigh density InAs QDs. When the QD height decreases below about 2 nm, those PL properties could be explained by strong in-plane coupling of wave functions between the QDs. (3)The type-II band structure of the GaAsSb/InAs QDs is one of useful structures to enhance the carrier lifetime in the QDs. In this year, the GaAs spacer layer was introduced between the GaAsSb capping layer and the InAs QDs. As a result, the crystal quality of the QD layer improved, and the PL decay time increased beyond 10 ns. (4)Based on these results, we fabricated the solar cells including one in-plane ultrahigh density InAs QD layer with a type-I or type-II band structure. The quantum efficiency of the type-II QD cell was higher than that of the type-I QD cell. However, the open circuit voltage of the type-II cell decreased because of the recombination loss through the non-radiative recombination centers and the hetero-interface of the GaAs/GaAsSb capping layer. Furthermore, we studied a relationship between the conversion efficiency and the position of the QD layer from the p-GaAs layer. As the separation distance from the p-layer decreases, the conversion efficiency improved (8 %).
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