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W: Oh it wasn't that. Hill made a big mistake in last month's accounting. Even if it wasn't really his fault, his boss was very angry.
Why did Hill lose his job？
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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 author is primarily concerned with ______.
What can be said about the way the man teaches the woman？
【C1】
Prices determine how resources are to be used. They are also the means by which products and services that are in limited supply are rationed among buyers. The price system of the United States is a very complex network composed of the prices of all the products bought and sold in the economy as well as those of a myriad of services, including labor, professions, transportation, and public-utility services. The interrelationship of all these prices make the “system” of prices. The price of any particular product or service is linked to a broad. complicated system of prices in which everything seems to depend more or less upon everything else. If one were to ask a group of randomly selected individuals to define "price", many would reply that price is an amount of money paid by the buyer to the seller of a product or service, or in other words, that price is the money value of a product or service as agreed upon in market transaction. This definition is, of course, valid as far as it goes. For a complete understanding of a price in a particular transaction, much more than the money involved must be known. Both the buyer and seller should be familiar with not only the money amount, but with the a- mount and quality of the product or service to be exchanged, the time and place at which the exchange will take place and payment will be made, the form. of money to be used, the credit terms and discounts that apply to the transaction, guarantees on the product or service, delivery terms, return privilege, and other factors. In other words, both the buyer and seller should be fully aware of all the factors that compose the total "package" being exchanged for the asked--for amount of money in order that they may evaluate a given price.
The best title for the passage is ______.
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