成果報告書詳細
管理番号20120000000156
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)高度秩序構造を有する薄膜多接合太陽電池の研究開発(配列制御ナノ結晶シリコン、メカニカルスタック)
公開日2012/6/20
報告書年度2011 - 2011
委託先名東京農工大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約
英文要約Title-1: Mechanical stack

Research contents and achievements:
1. In order to reduce thermal stress at the mechanical stuck process, we introduced epoxy-type comedienne transparent adhesive. Moreover, the sizes of ITO particles were selected using metal meshes. 20~25-μm sized ITO particles were successfully dispersed in cemedine transparent adhesive. Transmissivity was above 80% in visible and infrared regions.
2. In order to achieve mechanical stack with practical size, hydrostatic pressing method with a high pressure gas was developed. A pressure proof chamber with gas inlet and outlet was constructed. Nitrogen gas was introduced to increase gas pressure from 1.0 x105 to 4.0x105 Pa.
3. Combination of technologies shown above in 1 and 2 achieved stack of silicon substrates with a low connecting resistance of 1.8 Ωcm2 using 20~25-μm sized ITO particles dispersed in cemedine adhesive with a gas pressure of 3x105 Pa. Moreover, very fragile 4-inch diameter Ge and GaAs were successfully stacked. These results demonstrated the present technology had capability of mechanical stack solar cells with different kinds of cells with a large area.
4. We experimentally investigated polystyrene particles coated with 10 μm diameter Sn metal layers as low cost conductive particles, which NATOKO corporation developed. A low connecting resistance of 9.3 Ωcm2 was achieved the particles instead of ITO particles. Further optimization will decrease the low connecting resistance.

Title-2: Development of Nanocrystalline Silicon Top Cell

1. Outline of the Research and Development
(1) Development of nc-Si Fabrication Technology
Fabrication process of quantum-sized nanocrystalline silicon (nc-Si) membrane has been developed by wet-processing (anodization). Based on the establishment of wafer-compatible planar process for 4-inchwafer, large-area nc-Si membranes (8cm in diameter) have been lifted-off from pn-junction substrates by a sequential electrochemical technique. Mechanical stress in these membranes was successfully suppressed by introducing a super-critical drying method.
(2) Band Gap Tuning
Optical analyses of nc-Si membranes formed on pn-junction substrates indicated that the samples meet the band gap requirement for the use as a top cell in the multi-junction device. Also, it has been shown that by employing the current density modulation during anodization, the nc-Si membranes with a graded band profile can be fabricated.
(3) Photovoltaic Measurements
An nc-Si membrane cell fabricated on a pn-junction substrate showed a photovoltaic behavior with a significantly high open circuit voltage (0.84 V) under an AM1.5 illumination. This is due to a built-in field formed in the nc-Si layer. In addition, the spectral response of the nc-Si cell shows a clear blue shift compared with the on-substrate nc-Si cells. These experimental results suggest that the nc-Si is potentially useful for photovoltaic top-cell material with a wide band gap.
(4) Related Photonic Functions
The photon energy transfer in blue phosphorescent nc-Si samples was characterized in detail for a sample doped with dye molecules. Theoretical analysis of the avalanche photoconduction clearly indicates that both the hot electron generation rate and the impact ionization one are enhanced in nc-Si dots compared with those in bulk Si.

In summary, some important progresses and perspectives have been obtained from studies on the fabrication process, optical characterizations, and photovoltaic performance of nc-Si. To enhance the photoelectric conversion efficiency, the appropriate interfacial control of nc-Si dots will be intensively pursued.
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