成果報告書詳細
管理番号20130000000130
タイトル*平成24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
公開日2013/10/25
報告書年度2012 - 2012
委託先名独立行政法人産業技術総合研究所
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title: Exploring multi-junction thin-film solar cells with highly ordered structures (FY2008-2014) FY2012Annual Report

In order to obtain efficiency over 40%, we have studied highly ordered novel materials for optimized band gap and mechanically stacked two-terminal multi-junction solar cells. To achieve higher efficiency, the light management technologies including photonic structure, utilization of plasmon effect are also the research themes. Novel mechanical stacking technology is a must for fabricate two-terminal solar cell structure. Followings are some of the major results of research themes carried out in FY2012. 1-1-1: Development of mechanical stack and device fabrication technologies: A new direct bonding technique with conductive nanoparticle alignment has been developed. With this method, bonding resistance of below 2 Ωcm2 and optical absorption loss of 2 % were obtained simultaneously. Using this bonding method, GaInP /GaAs /InGaAsP 3-junction solar cells was fabricated and the total efficiency of 22.5% was attained. 1-2-1: Development advanced light management technologies: It was predicted by numerical simulations that a flattened light scattering substrate (FLiSS) with optimized design and materials enhances the short circuit current density of thin-film Si based solar cells by 40% compared to the FLiSS with our original structure. Based on this finding, a modified FLiSS was developed and the NIR response was enhanced by 23 %. 2-1-1: Development of Si-Ge bottom cells: Low dislocation density single-crystal SiGe film with high Ge content up to 70 % was successfully fabricated on Si substrate using stepwise compositionally graded buffer layers. As a result, improved quantum efficiency as well as conversion efficiency was obtained for a SiGe heterojunction solar cell with 50 % of Ge content (Eg ~1.0 eV). 2-3-1: Development of bottom cells using strongly-correlated materials: We evaluated diffusion lengths of photo carriers in lateral-type single-crystal devices with use of various molecular compound materials, and found that the diffusion length increases as the CT gap increases. On these bases, we successfully achieved material selection principle that enables both long carrier diffusion length and extended infrared photoelectric response. 3-2-1: Development of compound semiconductor top cells: We established a growth technique of InGaP films by a solid-source molecular beam epitaxy (MBE), and obtained a conversion efficiency of 12% for InGaP solar cells with a bandgap of 1.9 eV. An InGaP/GaAs double-junction solar cell with a high efficiency of 21.1 % and a high open circuit voltage of 2.3 V was obtained; such high performance InGaP/GaAs double junction solar cells were fabricated using solid-source MBE for the first time. Moreover, we obtained a conversion efficiency of 10% for InGaP-based InGaAs quantum dot (QD) solar cells. Formation of a miniband in a QD superlattice with an interdot spacing of 4.5 nm was confirmed experimentally by the excitation power dependence in photoluminescence measurements.
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