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Metals: Semiconductors

  • Page ID
    50937
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    Solar Polar using two basic types of semiconductors.

    The power of the sun could stand to power the world several times over theoretically. However, solar technology has not advanced to efficiently harness that potential. The key to solar power technology is to invent a mechanism to convert solar energy into electrical power. The photovoltaic effect led to the Nobel Prize in 1921 for Albert Einstein, and in the 1960s was used for military and satellites. Photovoltaic cells (PV, solar cells) convert radiant energy directly to electrical energy, without the intermediary of hydrogen or some other fuel. These cells are in the semiconductor family, meaning they normally do not conduct electricity well, but can do so under certain conditions. In order for PV to capture and store energy, the electric currents generated must have certain controllable properties. The process of “doping” is often used to achieve these properties by intentionally adding small amounts of other elements to pure silicon.

    Doping leads to two types of semiconductors:

    1. N-type semiconductors allow freely moving electrons. This process involves the addition of arsenic to the silicon to which allows the extra electrons to move easily through the lattice.

    2. P-type semiconductors allow freely moving positive charges called holes. This process uses the addition of gallium to silicon that causes the negative charged electron and the positively charged holes to move in opposite directions.

    P-type and n-type are often combined to directly aid in the conversion of sunlight to electricity. Sheets of n-type and p-type silicon are placed in contact causing the electrons to diffuse from the n-region to the p-region and the holes migrate from the p-region to the n-region. These p-n junctions facilitate the conduction of electricity and ensure that current flows in a specific direction.

    Although the concept sounds fairly simple, several challenges arise when creating silicon-based PVs. The first is that silicon is found as SiO2, and must be converted to a more pure form of silicon. Also, the efficiency associated with conversion of sunlight into electricity is low. The efficiency has increased from 15% in the mid-1970s to between 25% to 40.7% today. Research continues to push efficiency to higher marks through the use of solar concentrators and multi-junction cell arrays.

    In 1999, technology existed in photo-voltaic systems to provide all the energy needs of the United States. The problem with this technology was its feasibility. The plan assumed 10% efficiency and an area about the size of Nevada. Military research advances and commercialization of solar projects since 1999 have reduced the area needed and increased the efficiency of PV cells. Now, industry and military must take that increased efficiency and turn it into a commercially viable product.

    Figure \(\PageIndex{1}\). Schematic of the power unit of a solar panel.

    Figure \(\PageIndex{2}\). Picture of Solar One in Nevada. Electricity production is estimated to be 134 million kilowatt hours per year. It has a nominal capacity of 64 MW and maximum capacity of 75 MW spread over an area of 400 Acres. The projected CO2 emissions avoided is equivalent to taking approximately 20,000 cars off the road annually.

    From CoreChem: 22.0: Prelude to Metals

    References

    1. Eubanks, Lucy, P., et al. Chemistry in Context. Boston: McGraw-Hill, 2009.
    2. https://www.powerfromthesun.net/Book Accessed: 18 Jun 11.
    3. www.solarserver.de/wissen/photovoltaik-e.html Accessed: 17 Jun 11.
    4. www.energy.gov/news/4503.htm Accessed: 18 Jun 11.

    Contributors and Attributions


    This page titled Metals: Semiconductors is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Ed Vitz, John W. Moore, Justin Shorb, Xavier Prat-Resina, Tim Wendorff, & Adam Hahn.

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