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35th European Photovoltaic Solar Energy Conference and Exhibition; 20-22, Low concentration multi-junction (MJ) solar cells have a practical solution to consist with high efficiency and low cost. We have demonstrated a low concentration InGaP/GaAs//Si 3-junction solar cell with 23.74% at 8.0 suns using Smart Stack technology, which is a unique mechanical technology with Pd nanoparticle alignment. In this report, it is focused on the reduction of the bonding resistance. Especially, the bonding resistance at Pd/Si interface had become an important issue for low concentration performance. We examined the surface treatment of Si cell using Buffered Hydrogen Fluoride (BHF) solution. As a result, the bonding resistance at the high current density is reduced, and cell performance for low concentration was improved drastically. Using this technology, we fabricated an InGaP/GaAs//Si 3-junction solar cell and observed the maximum efficiency of 28.68% at 10.3 suns (AM1.5g). These results strongly suggested the high potential of our Smart Stack technology to achieve high efficiency GaAs//Si MJ solar cells for practical use.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 27-29, Low concentration multi-junction (MJ) solar cells have a practical solution to consist with high efficiency and low cost. We have demonstrated a low concentration InGaP/GaAs/Si 3-junction solar cell with mechanical stacking method. In this development, our key technology is the direct bonding using conductive nanoparticle alignment, which is named “Smart Stack” technology. Using this technology, we fabricated an InGaP/GaAs/Si 3-junction solar cell and observed the maximum efficiency of 23.74% at 8.0 suns (AM1.5g). In addition, we discuss the reliability of InGaP/GaAs/Si 3-junction solar cells showing the results of accelerated aging test and thermal cycling test. It was confirmed that our solar cells have high long-term reliability under sever conditions. Appling general lifetime estimation method with Arrhenius plot, the life time under 10 suns was estimated to be more than 1.5×105 hours at 60. These results strongly suggested the high potential of our Smart Stack technology to achieve low cost and highly reliable mechanically stacked MJ solar cells for practical use.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1390-1392, Low concentration multi-junction (MJ) solar cells have a practical solution to consist with high efficiency and low cost. This paper shows the demonstrations of low concentration GaAs/CuInGaSe(CIGSe) and GaAs/Si MJ solar cells with mechanical stacking method. Our key technology is the direct bonding using conductive nanoparticle alignment, which is named “Smart Stack” technology. The conductive nanoparticles, such as Pd, were aligned through the use of a self-assembled block copolymer template at the bonding interface. Therefore, sufficient reduction of bonding resistance and optical absorption loss can be simultaneously attained. Using this technology, we fabricated a GaAs/CIGSe 3-junction solar cell and observed the maximum efficiency of 25.3% at 5.7 suns (AM1.5g), which is concerned in proper increase of open circuit voltage (Voc) under the concentrated sun. This is the first demonstration as concentration examination for a two-terminal GaAs/CIGSe MJ solar cell. On the other hand, for a GaAs/Si 3-junction solar cell, maximum efficiency was 21.2% at 9 suns. According to our theoretical prediction, these efficiencies can be improved over 30% under the optimized structure design. The obtain results show the possibility of GaAs/CIGSe and GaAs/Si MJ solar cells as next generation solar cell.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 73-75, Smart stack is a handy method to construct multi-junction architectures through the interconnection of different types of solar cells using a Pd nanoparticle array as a bonding mediator. In this study, a triple-junction cell was fabricated from a InGaP/GaAs-based double-junction and a crystalline Si-based single-junction subcell using the smart stack approach. The simplest, matured, and widely-used Al-back surface field-type structure was particularly focused on for the Si bottom cell, and despite that, a promising efficiency of 20.9% was achieved as a smart stack InGaP/GaAs/Si device [short-circuit current density (Jsc), open-circuit voltage, and fill factor, were 9.65 mA/cm2, 2.75 V, and 0.790, respectively]. The EQE analysis of the smart stack cell was also carried out, which suggested that the device performance was limited by the Jsc generated at the GaAs subcell. Therefore, higher efficiencies are feasible through a regorous design and adjustment of each subcell, especially in terms of current matching.

第19回大気圏シンポジウム（2005年2月24日-25日. 宇宙航空研究開発機構宇宙科学研究本部（JAXA)(ISAS)）, 相模原市, 神奈川県, 19th Atmospheric Science Symposium (February 24-25, 2005. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 資料番号: SA6000131042

31st European Photovoltaic Solar Energy Conference and Exhibition; 1514-1516, In this paper, the so-called SMAC (SMart stacking with Areal current matching and Concentration) module concept is introduced as a cost-effective concentrator photovoltaic architecture for a multijunction (MJ) solar cell. In the SMAC module, a high-efficiency cell (e.g., a III-V MJ cell) is mechanically stacked on a larger-sized lowcost cell (e.g., an Si or CIGS cell). The current matching is managed by both the area ratio of the subcells and the concentrated illumination over the whole cell surface. Simulation results show that the conversion efficiency of the two-terminal tandem SMAC module (GaAs/InGaAsP, GaAs/CIGS, GaAs/Si) is greater than 30% and that the costeffectiveness of the SMAC module is improved by the appropriate irradiance distribution. In addition, the results show that the concentrator optics assist with the current matching of the subcells and reduce the top cell size, thereby resulting in a higher efficiency and lower cost. A proof-of-concept indoor experiment of the SMAC module (GaAs/InGaAsP) was performed. The experimental results demonstrate a trend similar to those of the simulation results.