How a solar cell is made

by Alyssa A. Lappen
Forbes | Aug. 15, 1983

Vol. 132, No. 15, p. 105
348 words

There are several types of solar cells, but they all work on the same principle: Semiconductorgrade silicon, formed into wafers, absorbs light, producing electrically charged particles and emitting a current that is collected through attached wires.

The most common production method is the Czochralski process, in which a large silicon crystal is “grown’ from a molten liquid in a furnace and then sliced into wafers. Raw polysilicon is melted to 2,200 degrees F, and a speck of silicon crystal is implanted. As the material is heated and turned, a sausagelike crystal emerges, up to 36 inches long and 150 pounds in weight. The wafers are sliced off by diamond blades and then processed into solar cells.

The Czochralski cells have over a 60% share of the market. The efficiency of panels of cells–the percentage of surface sunlight they turn into electricity–has reached a respectable 11%, even in mass production. But a prime disadvantage is the $45-per-kilogram cost of the raw material.

Semicrystalline cells make up about another 20% of the market. These are made chiefly by Solarex, a Rockville, Md. company that uses a “dirtier,’ less expensive polysilicon raw material. Instead of “growing’ crystals, Solarex casts the silicon into square ingots. The square wafers that are cut from the ingot have a better packing density and area efficiency on panels than their round Czochralski cousins. The semicrystalline cells get about a 10% to 12% efficiency when mass produced, but Solarex has produced cells in the lab that get about 18%. The company thinks it can reduce its cost to perhaps $5 per kilogram by the end of the decade by making its own silicon feedstock from quartz and sand.

Amorphous silicon solar cells have about 15% of the world market, but are only 5% to 6% efficient and are made primarily by the Japanese for consumer products like watches, calculators and battery chargers. American labs are working to improve this technology, too. Ribbon cells, made by Mobil Solar, resemble 2-inch steel ribbons and as yet account for less than 1% of the market.

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Alyssa A. Lappen is a U.S.-based investigative journalist. She is the former Managing Editor at the Leeb Group (2012-2017); a former Senior Fellow of the American Center for Democracy (2005-2008); and a former Senior Editor of Institutional Investor (1993-1999), Working Woman (1991-1993) and Corporate Finance (1991). She served six of her 12 years at Forbes (1978-1990) as an Associate Editor. Ms. Lappen was also a staff reporter at The New Haven Register (1975-1977). During a decade as a freelance, her work appeared in Big Peace, Pajamas Media, Front Page Magazine, American Thinker, Right Side News, Family Security Matters, the Washington Times and many other Internet and print journals. Ms. Lappen also contributed to the Terror Finance Blog, among others. She supports the right of journalists worldwide to write without fear or restriction on politics, governments, international affairs, terrorism, terror financing and religious support for terrorism, among other subjects. Ms. Lappen is also an accomplished poet. Her first full-length collection, The Minstrel's Song, was published by Cross-Cultural Communications in April 2015. Her poems have been published in the 2nd 2007 edition of Blood to Remember: American Poets on the Holocaust and both 2007 issues of Wales' award-winning Seventh Quarry: Swansea Poetry Magazine. Dozens of her poems have appeared in print and online literary journals and books. She won the 2000 annual Ruah: A Journal of Spiritual Poetry chapbook award and has received a Harvard Summer Poetry Prize and several honorable mentions.

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