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The Photoelectric EffectConverting Sunlight to Energy Via Photovoltaic CellsThe photoelectric effect can be harnessed to create energy from sunlight using photovoltaic cells.
Solar panels perform the seemingly magical task of converting sunlight into electricity that can be used by households and businesses. This feat is possible due to the photoelectric effect, a physical principle that converts the energy from photons in sunlight to electricity. The photoelectric effect is also known as the photovoltaic effect, and it's benefits are not limited to solar panels. This principle also contributes to the operation of light sensors, imaging devices, and night vision equipment. Photoelectric Effect BasicsAt its simplest, the photovoltaic effect describes how photons striking a metallic surface cause electrons in that metallic material to be knocked loose. In systems such as solar panels, the electrons can be captured as electricity. In situations where the electrons are not collected, such as in a spacecraft being struck by light, the object will have a net positive static charge, and systems have to be designed so that the static charge will not damage electronic equipment. In order for one electron to be released, the energy of the striking photon must be greater than work function of the electron. An electron must fully absorb the energy of one proton with high enough energy to be released from the metallic material. History of the Photoelectric EffectThe results of the photoelectric effects were observed as early as 1839 by Alexandre Edmond Becquerel, but the existence of electrons was not realized until 1899 when their existence was deduced by J. J. Thomson. Nikola Tesla refined the description of the photoelectric effect, but it was Albert Einstein who in his 1905 paper "On a Heuristic Viewpoint Concerning the Production and Transformation of Light", created the modern definition. It was this work that won Einstein the Nobel Prize in 1921. The major advancement put forth by Einstein was that the energy of the dislodged electrons was dependant on the frequency of the lightwaves that strike the object, rather than the intensity of the light. This theory was proved experimentally by Robert Andrews Millikan in 1915. Application of the Photoelectric EffectPutting the photoelectric effect to use requires a mechanism to capture the electrons as they are ejected from the metallic material. In the case of solar power, when a photon strikes a photocell, it knocks an electron from the valance band to the conduction band of the atoms in the photocell material. An n-tyype semiconductor contact collects the electrons from the conduction band as electricity. The electrons lose energy as they do work outside the system, and are then returned to the solar cell via a p-type semiconductor contact. Understanding the photoelectric effect has allowed engineers to harness the power of sunlight for a variety of applications. SourcesBurnett, The Basic Physics and Design of III-V Multijunction Solar Cells, 2002. Luque, Hegedus, Handbook of Photovoltaic Science and Engineering, Wiley, 2003.
The copyright of the article The Photoelectric Effect in Electrical Engineering is owned by Susan Kristoff. Permission to republish The Photoelectric Effect in print or online must be granted by the author in writing.
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