2005 Fiscal Year Final Research Report Summary
Low cost production of crystalline silicon thin films for solar cells by CVD process with closed gas recycling.
| Project/Area Number |
15206086
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Reaction engineering/Process system
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| Research Institution | The University of Tokyo |
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Principal Investigator |
OKABE Fumio The University of Tokyo, Graduate School of Engineering, Associate Professor, 大学院・工学系研究科, 助教授 (10345093)
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| Co-Investigator(Kenkyū-buntansha) |
NODA Suguru The University of Tokyo, Graduate School of Engineering, Assistant Professor, 大学院・工学系研究科, 助手 (50312997)
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| Project Period (FY) |
2003 – 2005
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| Keywords | crystalline silicon solar cells / silicon supply / reactant gas recycling / high yield process / chemical vapor deposition / physical vapor deposition / monocrystalline silicon thin films / epitaxial lift-off |
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| Research Abstract |
Large-scale photovoltaic power generation is essential to realize future clean energy systems. The bulk silicon type is promising owing to the abundant resource and excellent stability and safety of silicon. This type now accounts for 80- 90 % of the solar cells. High purity silicon is supplied from the semiconductor industry, and the amount of supply is now limiting the further enhancement of solar cell production. In this project, large-scale, low-cost production of solar cells was studied.
Silicon substrates are now industrially fabricated by slicing multi/monocrystalline silicon ingots, and an amount of silicon equivalent to about 500 μm thickness is consumed for each substrate. Substitution of substrates for thin films of 10 μm thickness can be a break through for scale enhancement and cost reduction of the solar cell production. We thus studied the epitaxial lift-off (ELO) method, in which a sacrificial layer and a monocrystalline silicon thin film are successively grown on a mono
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crystalline silicon wafer successively, the thin film and the wafer are separated by etching the sacrificial layer, and the thin film is used as the photovoltaic layer and the wafer is repeatedly used in this ELO process.
In the ELO process, the epitaxial growth method of the monocrystalline silicon photovoltaic layer is very important. Chemical vapor deposition (CVD) is usually used to grow micrometer-thick epitaxial films, but the utilization ratio of the chlorosilane source gases is small. Chlorosilanes are practically synthesized by reacting metallurgical grade silicon with hydrogen chloride. By recycling the outlet gas of CVD reactor into the reactor of chlorosilane synthesis, an ideal process can be realized in which metallurgical grade silicon is converted into monocrystalline silicon thin films with a minimal material loss. Literature survey of the current production process of chlorosilanes and experimental investigations of the reaction rate processes of chlorosilane synthesis and Si-CVD were performed in parallel, and feasibility of this "CVD process with closed gas recycling" was examined. But the problems came out such as possible contaminations into silicon thin films and degradation of the sacrificial layer used in ELO process. On the other hand, physical vapor deposition (PVD) was suggested effective in the ELO process. Based on a new concept of rapid vapor deposition (RVD), a silicon epitaxial growth rate as large as 10μm/min was confirmed at the substrate temperatures of 800-1000℃.
By coupling ELO and RVD processes, we succeeded to lift-off 5-10μm thick monocrystalline silicon thin films of a limited areal size. This is an achievement leading to the solution of the high-purity silicon shortage and the realization of large-scale, low-cost solar cell production. Less
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Research Products
(8 results)
