成果報告書詳細
管理番号20120000000812
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
公開日2012/11/28
報告書年度2011 - 2011
委託先名国立大学法人東京大学
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
II. 高効率量子タンデム太陽電池 製造プロセス技術開発
4.量子井戸ミドルセル
InGaAs/GaAsP量子井戸挿入GaAs単セルについて、量子井戸内で励起されたキャリアの電極への回収効率を、量子効率測定に基づいて評価する新手法を開発した。また、時間分解フォトルミネッセンスにより積層量子井戸におけるキャリア輸送過程を検討した。
英文要約Title:R&D on innovative Solar Cells Post-silicon solar cells for ultra-high efficiencies (FY2008-FY2012) FY2011 Annual Report
The structure of quantum-well cells has been optimized based on the kinetic analysis of carrier transport. Isc increment larger than 3.0 mA/cm2 and Voc drop smaller than 0.02 V were achieved, and the efficiency of a GaAs cell with quantum wells was enhanced to 24.0%. Voc of the cell increased to 1.1 V at 300 suns. The growth on Ge substrate was also attempted in order to implement quantum wells to a multi-junction cell. III-V-N(Sb) dilute nitrides, which can be tailored to lattice-match with a GaAs and Ge substrate and having an energy bandgap of 1eV were investigated in aim for realizing 4-junction tandem solar cells. Based on the results obtained in FY2010, we have developed a growth technique to fabricate a n-i-p GaInNAs(Sb) sub-cell on top of a Ge bottom cell to configure a double-junction structure. The GaInNAs(Sb) cell fabricated on GaAs reference has shown Jsc=22.3mA/cm2, Voc=0.42V, and FF=0.71, which is as good quality as the inverted p-i-n cell developed last year. Further, we can improve the quantum efficiencies in the longer wavelength region by increasing the GaInNAs(Sb) layer thickness. In the MOVPE growth of GaInNAs, the anti-phase domain (APD) formation has been successfully suppressed by using Ge(001) off-axis-to-[110] vicinal substrates. With a p-n junction consisting of a p-GaAs/i-GaInNAs/n-GaAs/n-Ge structure, a basic cell operation has been assured with Isc=1.5mA and VOC=0.40 V. Development of QD-based solar cells with metal nanoparticles (NPs) has been carried out toward plasmon-enhanced bottom cells for triple-junction solar cells. The IPCE value of QD-based solar cells without NPs reached 15% at 1100 nm by modifying the surface of QDs. Regarding the plasmon enhancement, the optimum NP size was 100 nm, and the enhancement peak wavelength red-shifted with increasing NP density. For an intermediate band solar cell (IBSC) which incorporates a quantum dot (QD) superlattice in the active region, it is important that the optical generation rates from IB to the conduction are maximized and matched to the generation rates from the valence band to IB. In FY2011, we have improved the fabrication technique to achieve higher QD stacks with lower defect densities, and to achieve improved size uniformity and periodicity by using (311)B high-index substrate as compared to (100). Further, InAs/GaNAs strain-compensated QDSC with 50 QD multi-stacks was tested under solar concentration. The cell conversion efficiency reached 20.3% at 100x suns and 21.2% at 1,000x suns. It should be possible to realize an efficiency of 35% under concentration by further increasing the density of quantum dots and improving cell structure with lower series resistance. Monolithic integration of GaAs cells in series connection has been demonstrated. A GaAs pn structure was grown on a semi-insulating GaAs substrate. Component cells were isolated by dry etching and interconnects were fabricated on the structure. 5-series connection was achieved successfully without significant performance degradation. Bypass diodes were also integrated with the series-connected cells. For the maximum photon incorporation to a photovoltaic cell in a optical concentrator module, the interfaces with minimum reflectance was designed. The backside structure to realize multiple reflections inside a quantum-structure cell has been investigated. Both arrayed grooves and metal nanoparticle assembly contributed to 30% increase of quantum efficiency for the nanostructure.
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