Photovoltaic cell is a semiconductor that generates electromotive force under light irradiationelement。It is an element that can generate electromotive force under the irradiation of light.It is used for photoelectric conversion, photoelectric detection and light energy utilization.[1]
Photocell is an element that can generate electromotive force under the irradiation of light.It is used for photoelectric conversion, photoelectric detection and light energy utilization.Selenium photocells were first discovered and applied.Its principle is that selenium generates electrons under the action of light and is collected by the electrode to generate electromotive force.Later, it discovered and applied various semiconductor materials of photocells, such as silicon photocells, silver sulfide batteries, etc.Its principle is that the p-n junction of the semiconductor generates new electron hole pairs under the action of light, and the electrons and holes move to both sides of the junction under the action of the p-n junction electric field to form an additional potential difference.[1]
principle
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Photocell
Photocell is also calledsolar energyBattery, which directly converts sunlight into electricity.Therefore, the characteristic of photocell is that it can convert a large amount of light energy absorbed by the earth from solar radiation into electric energy.It is produced under the irradiation of lightemfSemiconductorelement。There are many kinds of photocells, including selenium photocells, silicon photocells, thallium sulfide photocells, silver sulfide photocells, etc.It is mainly used for instrumentation, automatic telemetry and remote control.Some photocells can directly convert solar energy intoelectric energyThis kind of photocell is also calledSolar cell。Solar cells are widely used as energy in artificial earth satelliteslighthouse, unmanned weather station, etc
working principle
Photovoltaic power generationIs usingsemiconductorPn junctionPhotovoltaic effectIt is a technology that converts light energy directly into electric energy.The key elements of this technology areSolar cell(solar cell)。After the solar cells are connected in series, they can be packaged and protected to form a large areasolar cellModulepowerThe controller and other components form a photovoltaic power generation device.The advantage of photovoltaic power generation is that it is less restricted by the region, because the sun shines on the earth;PV systemIt is also safe, reliable, noiseless, low pollution, no fuel consumption and erectionTransmission lineIt can generate power locally and has the advantage of short construction period.Photovoltaic power generation is based on the principle of photovoltaic effect. When the P-N junction is illuminated, both intrinsic and extrinsic absorption of photons by the sample will occurPhotogenerated carrier。However, only a few carriers excited by intrinsic absorption can cause photovoltaic effect.The photogenerated holes generated in the P region and the photogenerated electrons generated in the N region are all multi carriers, which are blocked by the potential barrier and cannot cross junction.Only the photogenerated electrons in the P region and the photogenerated holes in the N region and the electron hole pairs (minority carriers) in the junction region can drift over the junction under the built-in electric field when they diffuse near the junction electric field.Photogenerated electrons are pulled to the N region, and photogenerated holes are pulled 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 region and photogenerated holes near the boundary of the P region.They generate a photogenerated electric field opposite to the direction of the built in electric field of the thermal balance P-N junction, and its direction is from the P region to the N region.This electric field lowers the potential barrier, which is the photogenerated potential difference. The P end is positive, and the N end is negative.So the junction current flows from area P to area N in the same direction asPhotocurrentcontrary.If the metal wires are welded on the P-type layer and N-type layer respectively, connectloadThen there will be current flowing through the external circuit. The battery elements formed in this way can be connected in series and parallel to generate a certain voltage, current and output power.
structure
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Photocell is a special semiconductor diode, which canvisible lightConvert toDC。Some photocells can also convert infrared light and ultraviolet light into direct current.Photocell is an integral part of solar power system, and solar power system is playing an increasingly important role in replacing electric energy.The earliest photocells were made of doped silicon oxide, and the purpose of doping was to affect the behavior of electrons or holes.Other materials, such as CIS, CdTe and GaAs, have also been developed and used as materials for photovoltaic cells.There are two basic types ofsemiconductor material , called positive (or P type) and negative (or N type) respectively.In a PV cell, the sheets of these materials are placed together, and the actual junction between them is called a P-N junction.With this structure, the P-N junction is exposed to visible light, infrared light or ultraviolet light. When the radiation irradiates the P-N junction, it is generated on both sides of the P-N junctionVoltage, so connected to theelectrodeThere will beelectric currentPassed.A set of PV cells can be connected together to form modules, rows or panels of the sun.The PV battery used to generate usable power isPhotoelectric voltmeter。One of the main advantages of the photoelectric voltmeter is that it has no pollution and only needs devices and sunlight to work.Another advantage is that solar energy is infinite.Once the photoelectric voltmeter system is installed, it can provide energy for several years without cost, and only requires minimal maintenance.
characteristic
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The photovoltaic power generation equipment is extremely refined, reliable, stable, long life, and easy to install and maintain.Monocrystalline silicon battery has high battery conversion efficiency, good stability, but high cost;Amorphous silicon solar cellIt has high production efficiency and low cost, but the conversion efficiency is low, and the efficiency decays severely;castingPolycrystalline silicon solar cellIt has stable conversion efficiency and the highest performance price ratio;filmCrystalline silicon solar cellIt is still in the research and development stage.
classification
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Power Supply
DC power supply can be divided into current power supply and voltage power supply. The characteristics of photocell are very close to the characteristics of ideal current power supply, which can be considered as ideal current power supply.
Battery
A. Single layer solar cell:
The photoelectric cell is like a "sandwich". The outer two layers are protective layers, and the middle layer is the main body
Silicon material composition.
siliconatomThe "Orbit electron" in is relatively loose and easy to be "Bombard" out.
This is similar to making semiconductors from silicon（Transistor）The considerations are the same.Then there is "silicon" everywhere,
It is cheap and "physical property" is stable.
Light is continuously emitted from the sun by "photons".
There are seven color frequencies (red, orange, yellow, green, blue, indigo, purple) in white light
Component light.Today's commercial "photocells" rely on "red light frequency".
The surface of the photocell allows only "red light to pass through" and reflects all its colored light.
Release, lead toconverter(Inverter *), DC becomes AC
(Alternating Current)。This AC power, like the power supply of the power company, can "illuminate"
Hot water, cooking, etc.
*It is the equivalent of "Rectifier".The rectifier can change alternating current into direct current.
The electricity "generated" by each household in the daytime cannot be used up and sold back to the power company.There is no electricity at night, buy from the power company!
In this way, families with "photocells" on the roof only pay a limited monthly electricity bill.Household negative?Greatly reduced.
B. Multi layer Solar Cell:
The efficiency of photocell with only one frequency is very low.Mover sent to Mars uses this kind of multi layer solar cell for more than three years, and it still works well.
purpose
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Photovoltaic power generation products are mainly used in three aspects: first, to provide power for non electric field, mainly to provide power for the living and production of residents in the vast area without power, as well as microwave relay power supply, communication power supply, etc., in addition, it also includes some mobile power supply and standby power supply;Second, solar daily electronic products, such as various solar chargersSolar street lampAnd solar lawn lamps;Third, grid connected power generation, which has been widely promoted in developed countries.China's grid connected power generation has not yet started, however,2008 Beijing Olympic GamesPart of the electricity will be supplied by solar power and wind power.
case
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Equivalent circuit of solar cell
Solar cells convert solar energy directly into electrical energy.PV power generation system is mainly composed of solar panel (module), controller andinverterThey are mainly composed of electronic components and do not involve mechanical components.Theoretically,Photovoltaic power generation technologyIt can be used in any occasion where power supply is needed, from spacecraft to household power supply, from megawatt power station to small power stationToysPV power is everywhere.Solar cells made of crystalline silicon materials mainly include: monocrystalline siliconpolysilicon , amorphous silicon and thin film batteries, etc.Cast polysilicon solar cells have replaced Czochralski monocrystalline silicon as the most important photovoltaic materials.However, the conversion efficiency of cast polysilicon solar cells is slightly lower than that of CzochralskiMonocrystalline silicon solar cellVarious defects in the materials, such as grain boundaries, dislocations, micro defects, and impurities in the materials, such as carbon and oxygen, as well as transition metals contaminated in the process are considered to be the key reasons for the low conversion efficiency of the battery. Therefore, research on the laws of defects and impurities in cast polysilicon, and the use of appropriate gettering in the process,Passivation process is the key to further improve the cast polysilicon battery.The conversion efficiency of mass produced monocrystalline silicon battery is about 17%, and that of polycrystalline silicon battery is about 16%.The conversion efficiency of thin-film battery in mass production is about 10%.
In addition to the commonly used single crystal, polycrystalline and amorphous silicon cells, multi-component solar cells are notelementSolar cells made of semiconductor materials.There are many kinds of research in various countries, most of which have not yet been industrialized, mainly including the following: a)Cadmium sulfide solar cell b)GaAs Solar Cell c) Copper Indium Selenium Solar Cells (New Multielement Band Gap Gradient Cu (In, Ga) Se2 Thin Film Solar Cells)
Development history
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In 1839, Antoine Becquerel produced the first photocell.Becquerel battery is a cylinder, which is filled with lead nitrate solution, and a lead is introduced into the solutionanodeAnd a copper oxidecathode。Once exposed to sunlight, this battery will supply current.
In 1875,GermanyTechnician Werner Siemens is the first selenium photocell made and proposed to be used for light measurement.Siemens' photocell is based on the British in 1873SmithFound "insidephotoelectric effect”Proposed.
50. H. Adams pointed out in 1876 that selenium not only appearedresistanceThe "barrier effect" is discovered by the change of the, and the electromotive force also appears under certain conditions.The barrier effect has become the basic principle of photocell.Photocells are widely usedAutomatic control technologyInformation electronics and measurement technology.The performance of these components has been around since 1950 becausesemiconductor technology Has been significantly improved.
