WHAT MATERIALS ARE USED TO MAKE PHOTOVOLTAIC CELLS?

Solar cells are made from many diff erent semiconductors. A semiconductor is a material that has the properties of an insulator as well as those of an excellent conductor. Some of the semiconductors used for making solar cells include silicon, gallium arsenide, copper indium diselenide, and cadmium telluride. All of these materials are suited to the development of solar cells to conduct electricity. 

CRYSTALLINE SILICON SOLAR CELLS 

Silicon (Si) is a semiconductor and the most common and important element in computer chip and solar technologies. It is a semimetallic, chemical element that crystallizes in a cubic shape similar to the pattern of a diamond. Silicon crystals are found in sand and quartz and are used extensively in the manufacturing of solar cells.

How Do Solar Cells Work? 

Most solar photovoltaic cells are made from two layers of crystalline silicon that have been chemically treated using a process called doping. Th e doping process gives one silicon layer a negative charge (N) and the other a positive charge (P). A solar cell is essentially a PN junction sandwiched between two layers of semiconductor materials. 

The process of producing electricity from a solar cell begins with sunlight. When the particles of light strike a solar cell, they cause electrons to be ejected from the silicon atoms. The electrons move freely from the negative layer to the positive layer through metal terminals producing electricity. A four-inch cell can produce about one watt of direct current. (Illustrator: Jeff Dixon)

Now how does the solar cell work? Th e process of producing electricity from a solar cell begins with sunlight, which contains energy in the form of photons or particles of light. When photons strike a solar cell, they cause electrons to be ejected from the silicon atoms located near the junction. An electron is a subatomic particle with a negative charge. Th e stream of ejected electrons can move freely from the negative layer to the positive layer through the metal terminals. 

How much electricity is generated from a solar cell? The typical fourinch solar cell can produce about one watt of direct current (DC) electricity when exposed to sunlight. To generate more electricity, you need to wire together many solar cells in a panel called a solar array that is encased in a watertight container for weather protection. If you need to produce a greater amount of electricity, then the panels, in turn, can be wired together. Th ese kinds of solar panels are placed on the roofs of homes and businesses to generate electricity. 

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John F. Mongillo
A Student Guide to Energy 
Copyright 2011
Greenwood Publishing Group
Volume 2 Solar Energy and Hydrogen Fuel Cells