| Project/Area Number |
17560291
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Electronic materials/Electric materials
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| Research Institution | Seikei University |
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Principal Investigator |
SAITO Yoji Seikei University, Science and Technology, Professor (90196022)
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| Co-Investigator(Kenkyū-buntansha) |
UEHARA Shingo Seikei University, Science and Technology, Professor (40232780)
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| Project Period (FY) |
2005 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥2,050,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥150,000)
Fiscal Year 2007: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000)
Fiscal Year 2006: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 2005: ¥800,000 (Direct Cost: ¥800,000)
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| Keywords | dry etching / silicon solar cells / multicrvstalline / texture / reflectivity / chlorine trifluoride / passivation / lifetime / 太陽光発電 / 反射損失 / 電子顕微鏡 / 反射スペクトル / ハニカム構造 / グループ構造 / 発電効率 |
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| Research Abstract |
The high conversion efficiency and the reduced cost have been required for the solar cells. One of the causes to suppress their efficiency is the surface reflection loss for the incident light. When the surface is rough, the incident light has more chance to go into the bulk, and the silicon surfaces have low reflectance. Single-crystalline silicon surfaces are usually textured to pyramid-like structures using an alkaline solution, utilizing the dependence of the etch rate on the crystalline - orientation. The texturization using an alkaline solution, however, is not applicable to multi-crystalline silicon wafers. The C1F_3 gas can etch silicon isotropically without plasma near room temperature, but hardly attacks silicon dioxide and positive-type photoresist films, as mask materials. Reflection loss of silicon solar cells can be reduced by texturization of the surfaces. In this study, single- and multi-crystalline silicon substrates were treated with chlorine trifluoride (C1F3) to create groove- and honeycomb-textured structures. We investigated surface structures and optical properties of the textured surfaces. By the treatment with C1F_3 gas, the reflectance of the textured surface without anti-reflection coating was obtained to be below 20% at wavelengths between 300 and 800 nm. The solar cells using the textured substrates were fabricated and their improved performances were demonstrated.
On the other hand, a number of the lattice defects in the multi-crystalline substrates degrade the solar cell performance. The short circuit current and conversion efficiency of the solar cells are increased by the passivation process using hydrogen plasma. The hydrogenation rate apparently increases at a reverse bias voltage near 0.6V during the hydrogenation process. The effects of the bias voltage on the hydrogenation are large at the substrate temperatures between 200C and 250C, and are considered to be caused by H^+ions, which would exist in the substrates.
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