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The photovoltaic effect is the process by which electrical current in the form of voltage is created when electromagnetic radiation is exposed to a certain material. Using solar cells, the photovoltaic effect occurs when very short wavelengths of sunlight impact the matter and electrons become excited. The electromagnetic radiation is emitted from the solar panel and collected by another material. This ejection of electrons results in the buildup of voltage creating energy that can be stored in a battery cell for later use. Two electrodes are used to collect the voltage, which can be transferred into the power grid.
Different types of electromagnetic radiation cause different exposure levels in solar cells as a result of frequency. Visible light creates the photovoltaic effect when it impacts alkali metals, ultraviolet light creates it in other metals, with extreme ultraviolet light being used for non-metals. This concept was first observed in 1902 by Philipp Eduard Anton von Lenard when he discovered that different colors of light, also known as frequency, emit different levels of electrons. Previously, the wave theory of light by James Clerk Maxwell stated that radiation intensity would create proportional electron energy. This new theory explained that photons were responsible for the creation of electron ejection and worked as individual particles rather than constant waves.
Physicist A.E. Becquerel recognized the concept of the sunlight photovoltaic effect in 1839, but his understanding was limited. In 1883, Charles Fritts constructed the first solar cell, using a selenium semiconductor coated in a thin layer of gold. This first use of a solar cell was only one percent efficient. It wasn't until 1954 that Bell Laboratories developed a practical way to harness solar energy.
The way the photovoltaic effect is harnessed using solar cells is very basic. Essentially, photons from the sunlight impact the solar panel and are absorbed by the material. The negatively charged electrons within the material are knocked away from the atoms, which then produces electricity. This situation is controlled by allowing the electrons to move in only one direction in the panel, causing a reverse action in which positively charged particles flow in the opposite direction. With both of these actions occurring, a direct current of electricity can be harnessed from the electromagnetic reaction.
The photovoltaic effect is essential for a number of processes in modern life. In addition to energy creation for general purposes, solar cells are essential to spacecraft used by NASA and other space agencies. Also, the principles of the technology are utilized in digital cameras in the form of charge-coupled devices as well as electroscopes that identify static electricity.