Chlorine chemistry is imperative to purifying silicon used to make both solar cells and integrated circuits, the foundation of modern electronics.

A Partnership with the Sun

For centuries, humans have taken advantage of the tremendous energy of the sun. Besides powering the growth of crops, solar energy has long been used to dry foods for long-term storage, dry the family laundry, and whiten fabrics. But advances in science and technology have brought us to a new day in our partnership with the sun. Today’s solar energy panels convert sunlight directly into useful energy in the form of electricity. It is a feat that would amaze our ancestors.

At the heart of most solar energy panels is a series of high-purity silicon solar cells, small, interconnected energy-generating units. Currently, more than 95 percent of all solar cells are produced from the chemical element silicon. Chlorine chemistry is essential to purifying silicon used to make both solar cells and integrated circuits, the foundation of modern electronics. According to a 2006 study, using chlorine chemistry to produce high purity silicon for integrated circuits and solar cells saves U.S. and Canadian consumers about $15.5 billion each year.

Solar Cells: A Closer Look

Because of its unique internal atomic structure and its ready availability, silicon is widely used for solar cells. One of the elements of the Periodic Table of the Elements, silicon is known as a semiconductor, a substance that conducts electricity when there is a change to its environment. In a solar cell, energy absorbed from sunlight causes tiny, negatively charged electrons to be knocked loose from silicon atoms and made to flow through the material, generating electricity. This phenomenon is known as the photovoltaic effect.

An “In-and-Out” Role for Chlorine Chemistry

Purified silicon is used to manufacture solar cells. Chlorine chemistry plays an important “in-and-out” role in purifying silicon, in the form of chlorine-containing hydrochloric acid (HCl). Hydrochloric acid is combined with impure silicon—derived from quartz sand—at 300 degrees C (572 degrees F), to produce trichlorosilane, the compound HSiCl3. Trichlorosilane is then heated to a much higher temperature, 1150 degrees C (2102 degrees F), at which point it decomposes. One of the products of its decomposition is very pure silicon. Another is hydrochloric acid, which is recycled back into the process.

Solar Energy Outlook

Among 21st century energy resources, renewable solar energy is a relatively minor player, but one that is growing in importance. Solar energy panels are becoming common sights across the landscape, powering everything from traffic lights to art installations. They are ingeniously used to power communications satellites in space and the Mars rovers exploring the Red Planet. Increasingly, they are being installed on the sides of buildings and on rooftops, reducing the demand for more traditional energy sources.

Our ability to harness solar energy more efficiently and economically over time will depend upon how well we apply the tools of chemistry and physics available to us. So far, chlorine chemistry has proven an essential chemistry in developing solar energy panels.

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