الفهرس 
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Abstract
In recent years,the field of solar enol-gy conversion has achieved successful development and applications. The use of solar cells for space applications started during 1960’s when there was a demand for electric power in space environment for supplying the space satellites. However,
it has been only in the last few years that the solar cells have started for terrestrial applications.
The main problem today is to decrease the cost per unit power output from the solar cell panels. The major part of the cost of a solar panel is spent to produce the single crystal semiconductor material used in constructing the solar cell. Therefore,many research efforts have been spent on new semiconductor materials available for solar cells also many studies have been carried out on polycrystalline,and amorphous semiconductors of low preparation costs to solve the high cost problem blocking the economical use of solar cells.
One of the semiconductor materials which has shown accep¬table performance in the solar energy conversion field is the amorphous silicon (a–Si),due to its low production cost compared to single crystal one, and acceptable electrical properties compared to other amorphous semiconductors.