What is a solar cell?

2021-07-27 11:09:42

What is a solar cell?
Photovoltaic cells are also called solar cells, which directly convert sunlight into electricity. Therefore, the characteristic of the photovoltaic cell is that it can convert the large amount of light energy absorbed by the earth from solar radiation into electrical energy. It is a semiconductor element that generates electromotive force under the irradiation of light. There are many types of photovoltaic cells, such as selenium photovoltaic cells, silicon photovoltaic cells, thallium sulfide, and silver sulfide photovoltaic cells. Mainly used in instrumentation, automatic telemetry and remote control. Some photovoltaic cells can directly convert solar energy into electrical energy. This kind of photovoltaic cell is also called solar cell. Solar cells are widely used as energy sources in artificial earth satellites, lighthouses, unmanned weather stations, etc.

Photovoltaic power generation is a technology that uses the photovoltaic effect of semiconductor pn junctions to directly convert light energy into electrical energy. The key element of this technology is the solar cell (solar cell). After the solar cells are connected in series, they can be encapsulated and protected to form a large-area solar cell module (module), and combined with power controllers and other components to form a photovoltaic power generation device. The advantage of photovoltaic power generation is that it is less geographically restricted, because the sun shines on the earth; photovoltaic systems also have the advantages of safety, reliability, noiselessness, low pollution, no need to consume fuel and erect transmission lines to generate power on site, and the construction period is short.

Photovoltaic power generation is based on the principle of photovoltaic effect. When the P-N junction is exposed to light, both the intrinsic absorption and extrinsic absorption of photons by the sample will generate photo-generated carriers. But it is only the minority carriers excited by intrinsic absorption that can cause the photovoltaic effect. Due to the photo-generated holes generated in the P region and the photo-generated electrons generated in the N region are many sons, they are all blocked by the barrier and cannot pass through the junction. Only the photogenerated electrons in the P zone and the photogenerated holes in the N zone and the electron-hole pairs (minority carriers) in the junction zone can drift through the junction under the action of the built-in electric field when they diffuse to the vicinity of the junction electric field. The photo-generated electrons are drawn to the N region, and the photo-generated holes are drawn to the P region, that is, the electron-hole pairs are separated by the built-in electric field. This leads to the accumulation of photogenerated electrons near the boundary of the N zone and the accumulation of photogenerated holes near the boundary of the P zone. They generate a photogenerated electric field that is opposite to the built-in electric field of the thermally balanced P-N junction, and its direction is from the P zone to the N zone. This electric field lowers the potential barrier, and the reduction is the photo-generated potential difference. The P terminal is positive and the N terminal is negative. Therefore, the junction current flows from the P area to the N area, and its direction is opposite to the photocurrent.

If metal wires are welded to the P-type layer and the N-type layer at this time, and the load is connected, current will flow through the external circuit. The battery elements formed in this way can be connected in series and parallel to generate a certain voltage. And current, output power.
 
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