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  3. The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving

The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving

admin2010-01-18  79
问题    The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving parts. The basic problem with the use of solar photo-voltaic devices is economic, but until recently very little progress has been made toward the development of low-cost photo-voltaic devices. The larger part of the research funding has been devoted to study of single-crystal silicon solar cells, despite the evidence, including that of the leading manufacturers of crystalline silicon, that the technique holds little promise. The reason for this pattern is understandable and historical. Crystalline silicon is the active element in the very successful semiconductor industry, and virtually all of the solid state devices contain silicon transistors and diodes. Crystalline silicon, however, is particularly unsuitable to terrestrial solar cells.
   Crystalline silicon solar cells work well and are successfully used in the space program, where cost is not an issue. While single-crystal silicon had been proven in extraterrestrial use with efficiencies as high as 18 per- cent, and other more expensive and scarce materials such as gallium arsenide can have even higher efficiencies, costs must be reduced by a factor of more than 100 to make them practical for commercial use. Besides the fact that the starting crystalline silicon is expensive, 95 percent of it is wasted and does not appear in the final de- vice. Recently, there have been some imaginative attempts to make polycrystalline and ribbon silicon, which are lower in cost than high-quality single-crystals; but to date the efficiencies of these apparently lower-cost arrays have been unacceptably small. Moreover, these materials are cheaper only because of the introduction of disordering in crystalline semiconductors, and disorder degrades the efficiencies of crystalline solar cells.
   This dilemma can be avoided by preparing completely disordered or amorphous materials. Amorphous materials have disordered atomic structure as compared to crystalline materials: that is, they have only short-range order rather than the long-range periodicity of crystals. The advantages of amorphous solar cells are impressive. Whereas crystals can be grown as wafers about four inches in diameter, amorphous materials can be grown over large areas in a single process. Whereas crystalline silicon must be made 200 micron of the proper amorphous materials in necessary. Crystalline silicon solar cells cost in excess of $ 100 per square foot, but amorphous films can be created at a cost of about 50 cents per square foot.
   Although many scientists were aware of the very low cost of amorphous solar cells, they felt that they could never be manufactured with the efficiencies necessary to contribute significantly to the demand for electric power. This was based on a misconception about the feature which determines efficiency. For example, it is not the conductivity of the material in the dark which is relevant, but only the photo-conductivity, that is, the conductivity in the presence of sunlight.
   Already, solar cells with efficiencies well above 6 percent have been developed using amorphous materials, and further research will doubtlessly find even less costly amorphous materials with higher efficiencies.
The material in the passage could best be used in an argument for ______.
选项 A、increased funding for research on amorphous materials
B、further study of the history of silicon crystals
C、increased reliance on solar energy
D、training more scientists to study energy problems
答案A
解析 主旨大意题。作者在文中提出了一种能够大大降低photo-voltaic装置成本的材料amorphous materials，对人类更好的利用太阳能很有意义。文章结尾作者还指出目前的研究已经取得了初步进展，如果再进一步研究一定能发现更高效，成本更低的同类材料。本文如果作为对amorphous materials研究给予资金支持的申请，是相当令人信服的。因此A是正确答案。
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