成果報告書詳細
管理番号20110000000647
タイトル*平成22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)高度秩序構造を有する薄膜多接合太陽電池の研究開発(強相関材料)
公開日2011/8/30
報告書年度2010 - 2010
委託先名独立行政法人理化学研究所
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 (1) 研究の目的と概要(平成20~22年度) 本研究では、バンドギャップより大きなエネルギーを持つ1つの光子から、複数の電子・正孔対を生成して(図1左図)太陽電池の効率を向上する新材料として、強相関電子酸化物の可能性を検証することを目的としている。このような多重キャリア生成には、閉じこめ効果による電子相関効果の増強効果が必要であるため、半導体ナノ粒子を対象とした基礎研究が行われてきた。
英文要約Title: Exploring multi-junction thin-film solar cells with highly ordered structures (FY2008-2010) FY2010 Annual Report
The aim of this research project is to verify the possibility of generating multiple carriers by single high energy photon excitation in correlated electron oxides and extracting these carriers as photocurrent by the internal electric field in heterojunction. Multiple carrier generation is one of the most challenging and promising routes to accomplish substantially high efficiency in future photovoltaics. However, current research is focused on pump-probe experiments using narrow band gap semiconductor nano-particles dispersed in liquid as a colloidal solution to detect multiple exciton generation. This unrealistic system has to be chosen because semiconductor has very low electron correlation. Yet the possibility is unknown, we would like to make use of strong electron correlation is transition metal oxides.
As the research in FY H-22, we set the following research targets and have obtained respective results.
(1) Up to last year, we constructed a two-dimensional model system considering spin-exchange and transfer that can be used for time-development of the system as theoretical research. This year, the system was used to examine multiple carrier generation. When we set antiferromagnetic exchange energy rather small, the system was transferred to ferromagnetic metallic state, where we observed clear sign of amplification in members of photo-excited carriers. This analysis was compared with realistic compound with use of experimentally developed phase diagram to clarify suitable system for demonstration experiments.
(2) The nano-scale distribution of metal-insulator transition of correlated oxides is not clarified yet. We employ microwave microscope to reveal real-space distribution. We fabricated (NdSr)MnO3 thin films as a model system. Directional propagation of metallic patches with a width of 50nm were observed upon magnetic-filed induced metallization. Interestingly, these nano-wires run a certain crystallographic directions. This knowledge is useful for designing correlated electron solar cells.
(3) As another candidate of solar cell material, we examined (VW)O2 under X-ray irradiation. We found that x-ray indeed van induce insulator to metal transition and surprisingly, the yield is 105 per one photon. We will extend this study to examine multiple carrier generation with use of visible light.
(4) Last year, we characterized LaMnO3/Nb:SrTiO3 solar cells as one of the most promising candidates. There, the total width of depletion layer and diffusion length was estimated to be about 10nm. This year, we analyzed the bias voltage dependence and elucidated that these layer width is nearly the same. This knowledge gives us a guide to design the solar cells.
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