Category: Education/Science >> Science and Technology
Problem Description:
Why can solar cells convert sunlight into electricity ?
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Analysis:
The effect of a beam of light on a semiconductor is completely different from that on a metal or insulator. . Because there are so many free electrons in metals, changes in conductive properties caused by light are completely negligible. Insulators still fail to stimulate more electrons to conduct electricity at very high temperatures. The binding force of semiconductors, whose conductivity is between metals and insulators, on the body's electrons is much lower than that of insulators. The photon energy of visible light can prevent it from binding to a free conducting state. semiconductors. When an electric field exist in a local area inside a semiconductor, photogenerated carriers accumulate, which is very different from the absence of an electric field. A photoelectric voltage is generated on both sides of the electric field due to the accumulation of charges. photovoltaic effect, or photovoltaic effect for short. Solar cells are manufactured using this effect.
When sunlight hits a semiconductor, some of it is reflected by the surface and the rest is absorbed or transmitted by the semiconductor. Of course, part of the absorbed light turns into heat and other photons collide with the valence electrons of the atoms that make up the semiconductor, thus generating electron-hole pairs. In this way, light energy is converted into electrical energy in the form of electron-hole pairs. If there is a P-n junction in the semiconductor, a barred electric fieldre is formed on both sides of the P-type and N-type interface. which can conduct electrons to the n region. The holes are directed toward the P region, so that there are excess electrons in the n region and excess holes in the P region, forming an electric field of light opposite the direction of the barrier. electric field near the P-n junction. In addition to compensating the barrier electric field, part of the photogenerated electric field also charges the positively charged P-type layer and the negatively charged N-type layer, thus creating a so-called photovoltaic electromotive force in the thin layer between the n region. and the region p. If metal wires are soldered to the P-type layer and the N-type layer respectively and the load is connected, the current will flow through the external circuit. The battery components thus formed can produce a certain voltage, a certain current and a certain powerthis output by connecting them in series or parallel.