![]() ![]() ![]() The voltage produced by solar cells varies with the wavelength of incident light, but typical cells are designed to use the broad spectrum of daylight provided by the sun. The final result is production of electrical power derived directly from the energy of light. In the construction of a photovoltaic cell, metal contact layers are applied to the outer faces of the two semiconductor layers, and provide a path to the external circuit that connects the two layers. By providing an external circuit by which the electrons can return to the other layer, a current flow is produced that will continue as long as light strikes the solar cell. ![]() Towards this end, the electrons will follow another path if one is available. Electrons being swept into the n-layer by the localized effects of the fixed field have a natural tendency to leave the layer in order to correct the charge imbalance. Because the electrons can easily cross the boundary, but cannot return in the other direction (against the field gradient), a charge imbalance results between the two semiconductor regions. Electrons close to the boundary (the p-n junction) can be swept across the junction by the fixed field. When light of an appropriate wavelength (and energy) strikes the layered cell and is absorbed, electrons are freed to travel randomly. As the electrical imbalance reaches an equilibrium condition, a fixed electric field results across the boundary separating the two sides. The combining of electrons and holes at the p-n junction creates a barrier that makes it increasingly difficult for additional electrons to cross. #Light bulb powered by copper solarcell free#When the two dissimilar semiconductor layers are joined at a common boundary, the free electrons in the n-layer cross into the p-layer in an attempt to fill the electron holes. One layer is modified to have excess free electrons (termed an n-layer), while the other layer is treated to have an excess of electron holes or vacancies (a p-layer). In a typical photovoltaic cell, two layers of doped silicon semiconductor are tightly bonded together (illustrated in Figure 1). Silicon that has been doped in this manner has sufficient photosensitivity to be useful in photovoltaic applications. Because both holes and electrons are mobile within the fixed silicon crystalline lattice, they can combine to neutralize each other under the influence of an electrical potential. However, silicon can be modified by adding specific impurities that will either increase the number of free electrons ( n-silicon), or the number of holes (missing electrons also referred to as p-silicon). Functioning as free carriers, the electrons are capable of producing an electrical current, although in pure silicon there are so few of them that current levels would be insignificant. These freed electrons move about randomly through the solid material searching for another hole with which to combine and release their excess energy. In pure silicon, when sufficient energy is added (for example, by heating), some electrons in the silicon atoms can break free from their bonds in the crystal, leaving behind a hole in an atom's electronic structure. Their function depends upon the movement of charge-carrying entities between successive silicon layers. Today, the most common photovoltaic cells employ several layers of doped silicon, the same semiconductor material used to make computer chips. In order to increase or decrease the photon flux, use the Photon Intensity slider to adjust the number of photons incident on the surface. The released electrons complete a simple circuit containing two light bulbs that become illuminated when current flows through. The tutorial initializes at an arbitrarily set "medium" photon intensity level, with photons randomly impacting the surface of the solar cell to generate free electrons. This tutorial explores the basic concepts behind solar cell operation. The voltage produced in the cell is capable of driving a current through an external electrical circuit that can be utilized to power electrical devices. The most common types of solar cells are based on the photovoltaic effect, which occurs when light falling on a two-layer semiconductor material produces a potential difference, or voltage, between the two layers. Solar cells convert light energy into electrical energy either indirectly by first converting it into heat, or through a direct process known as the photovoltaic effect. Interactive Tutorials Solar Cell Operation Molecular Expressions Microscopy Primer: Physics of Light and Color - Solar Cell Operation: Interactive Tutorial ![]()
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