Solar cells, which can effectively absorbsolar energyAnd convert it into electric energy.Using semiconductorssilicon﹑seleniumA device that converts the light energy of the sun into electrical energy.It has the advantages of high reliability, long service life, high conversion efficiency, etcArtificial satellite, beacon lighttransistor radioAnd so on.The size of the single battery ranges from 1 × 1cm to 15.6 × 15.6cm, and the output power is tens of megawatts to several wattsPhotoelectric conversion efficiencyMore than 25%, actually more than 22%.
Chinese name
solar cell
Foreign name
solar cell
Phonetic transcription
tài yáng diàn chí
Interpretation
Absorb solar energy and convert it into electric energy
Solar cell is a kind of utilizationPhotovoltaic effectA device that converts light energy into electrical energy, also calledPhotovoltaic devices, mainly includingmonocrystalline siliconBattery and single crystalGallium arsenideBattery, etc.Solar cells were originally used for space spacecraftMonocrystalline silicon solar cellThe basic material of is P-type monocrystalline silicon with a purity of 0.999999 and a resistivity of more than 10 ohm cm, including p-n junction, electrode, antireflection film and other parts. The illuminated surface is protected by a transparent cover (such as quartz or cerium infiltrated glass) to prevent the battery from being damaged by the radiation of high-energy electrons and protons in the Van Allen band in outer space.The size of single battery ranges from 2 × 2cm to 5.9 × 5.9cm, and the output power is tens to hundreds of milliwattsPhotoelectric conversion efficiencyMore than 20%, actually more than 15%.
single crystalGallium arsenideThe theoretical photoelectric conversion efficiency of the solar cell is 24%, and the actual efficiency is 18%.It canHigh light intensityThe radiation damage resistance is higher than that of silicon solar cells, but the output of gallium is less and the cost is high.Cascaded p-n junction solar cell is a p-n junction with multiple different band gap materials superimposed on a substrate. The top junction with large band gap is close to the illumination surface to absorb short wave light, and the lower band gap decreases in turn, and the wavelength of the absorbed light wave gradually increases. This kind of cell can make full use of sunlight, and the photoelectric conversion efficiency is greatly improved.
To improveSingle solar cellIt can take measures such as shallow junction, dense grid, back electric field, back reflection, textured surface and multilayer film to increase the area of single cell, which is beneficial to reduce the number of solar cell arraysweldingPoint to improve reliability.
Development history
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China's first solar cell
The development history of solar cells can be traced back to 1839, when Alexander Edmond Becquerel, a French physicist, discovered the Photovoltaic effect.It was not until 1883 that the first selenium solar cell was manufactured by Charles Frits, an American scientist.In the 1930s, selenium batteries andCupric oxideBatteries have been used in some light sensitive instruments, such as photometers and exposure pins of cameras.The modern silicon solar cell was developed by Russell Ohl, a semiconductor researcher, in 1946.Then in 1954, scientists increased the conversion efficiency of silicon solar cells to about 4%, and the next year to 11%.Subsequently, solar cells were applied to artificial satellites.
After the energy crisis in 1973, human began to turn solar cells to civilian use.It was first used in calculators and watches.In 1974, Haynos et al. used the anisotropic etching characteristics of silicon to etch the textured surface with many pyramidal structures on the surface of monocrystalline silicon solar cells.Pyramid textured structure can effectively reduce the reflection loss of sunlight on the battery surface, making the conversion efficiency of solar cells at that time reach 17%.
Since 1976, how to reduce the cost of solar cells has become the focus of the industry.After 1990, the reduction of battery cost made solar cells enter the field of private power generation, and solar cells began to be used for grid connected power generation.
classification
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classification
Classified solar cells are the core of photovoltaic power generation system.According to the maturity of production technology, solar cells can be divided into the following stages:
The first generation of solar cells: crystalline silicon cells;
Second generation solar cells: various thin film batteries.Including amorphous silicon thin film battery (a-Si), cadmium telluride solar cell (CdTe), copper indium gallium selenium solar cell (CIGS), gallium arsenide solar cellNano titanium dioxideDye sensitized solar cell, etc;
The third generation of solar cells: various super stack solar cells, thermal photovoltaic cells (TPV), quantum well and quantum dot superlattice solar cells, intermediate band solar cells, up conversion solar cells, down conversion solar cells, hot carrier solar cells, collision ionization solar cells and other new concept solar cells.
According to the cell structure, solar cells can be divided into crystalline silicon solar cells and thin film solar cells.
According to the basic materials used, solar cells can be divided into silicon solar cells, compound solar cellsDye-sensitized cellAnd organic thin film batteries.
Developments
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Silicon based solar cell
Silicon based batteries include polycrystalline silicon, monocrystalline silicon and amorphous silicon batteries.The efficiency of industrialized crystalline silicon cells can reach 14%~20% (16%~20% for monocrystalline silicon cells and 14%~16% for polycrystalline silicon cells).At present, polycrystalline silicon and monocrystalline silicon solar cells account for nearly 90% of industrialized solar cells.Silicon based batteries are widely used in grid connected power generation, off grid power generation, commercial applications and other fields.
Single crystal solar panel
(1)Monocrystalline silicon solar cell[1]In the single crystal solar panel silicon series solar cells, the single crystal silicon large solar energy cells have the highest conversion efficiency (16%~20%) and the most mature technology.At present, the electrogrounding process of monocrystalline silicon is nearly mature. In the production of batteries, surface texturing, emission region passivation, zoning doping and other technologies are generally used. The developed batteries mainly include planar monocrystalline silicon cells and grooved buried grid electrode monocrystalline silicon cells.
The main ways to improve the conversion efficiency are the surface microstructure treatment of monocrystalline silicon and the zoning doping process.In this regard, the German Fraunhofer Freiburg Solar Energy System Research Institute maintains the world's leading level.The research institute uses photolithography technology to texture the battery surface and makeInverted Pyramid 。A 13nm thick oxide passivation layer is combined with two antireflection coatings on the surface, and the ratio of gate width and height is increased through the improved electroplating process.The conversion efficiency of the large area (225cm2) single crystal solar cell prepared by Kyocera is 19.44%Beijing Solar Energy Research InstituteAnd actively carry out high efficiencyCrystalline silicon solar cellThe conversion efficiency of the developed planar high-efficiency monocrystalline silicon cell (2cm × 2cm) reached 19.79%, and the conversion efficiency of the grooved buried gate electrode crystalline silicon cell (5cm × 5cm) reached 18.6%.The conversion efficiency of monocrystalline silicon solar cells is undoubtedly the highest and still occupies a leading position in large-scale applications and industrial production. However, due to the influence of the price of monocrystalline silicon materials and the corresponding cumbersome battery processes, the cost price of monocrystalline silicon remains high.
Polycrystalline silicon solar cells have low cost, high conversion efficiency (14%~16%), mature production process, occupy the main photovoltaic market, and are now the leading products of solar cells.Polycrystalline silicon solar cells have become the mainstream technology with the highest share of solar cells in the world.However, the efficiency of polycrystalline silicon solar cells is lower than that of monocrystalline silicon solar cells.Comparing the power generation efficiency per unit cost, the two are close.
The advantage of amorphous silicon is that it has a strong light absorption ability for the visible spectrum (500 times stronger than crystalline silicon), so only a thin layer can effectively absorb the energy of photons.And thisAmorphous silicon filmThe production technology is very mature, which can not only save a lot of material costs, but also make it possible to produce large-area solar cells.The main disadvantage is that the conversion rate is low (5% - 7%), and there is light induced decay (the so-called S-W effect, that is, the photoelectric conversion efficiency will decay with the duration of light, making the battery performance unstable).Therefore, it is not competitive in the solar power generation market, and is mostly used in the small sub type electronic product market with low power.asElectronic calculator, toys, etc.
In the 1980s, amorphous silicon was the only commercialized thin-film solar cell material. When amorphous silicon solar cells appeared, it caused a lot of investment.From 1985 to the beginning of 1990, the proportion of amorphous silicon solar cells once reached one third of the global total solar cells, but later, due to poor stability, it failed to get effective improvement, leading to a decline in output.
Thin film solar cell
According to different materials, thin film batteries[2]It can be subdivided into: Thin Film Crystalline Silicon Solar Cell (c-Si);Thin Film Amorphous Silicon Solar Cell (a-Si for short), Group Ⅱ - Ⅵ compound solar cells (CdTe, Indium Copper Selenide), Group Ⅲ - Ⅴ compound solar cells, such as gallium arsenide (GaAs), indium phosphide (InP), gallium indium phosphide (InGaP).In addition to the Ⅲ - Ⅴ compound solar cells, which can use the multi-layer film structure to achieve a conversion efficiency of more than 30%, the efficiency of other concentrated thin film solar cells is generally less than 10%.
At present, there are three kinds of industrialized thin film photovoltaic cell materials: amorphous silicon (a-Si), copper indium selenium (CIS, CIGS) and cadmium telluride (CdTe),Amorphous silicon thin film batteryThe proportion of production is the largest.In 2007, it accounted for 5.2% of the global total output.
(1) Ⅲ - Ⅴ compound solar cells
Typical Ⅲ - Ⅴ compound solar cells are gallium arsenide (GaAs) cells, with a conversion rate of more than 30%. This is because Ⅲ - Ⅴ compounds are semiconductor materials with direct energy gap. Only 2um thick, they can absorb about 97% light under AM1 radiation conditions.Thin film solar cells made of GaAs thin films grown by chemical vapor deposition on monocrystalline silicon substrates are used in space due to their high efficiency.However, the new generation GaAS multi junction solar cells have the highest conversion efficiency because of their high absorbable spectral range, so their conversion efficiency can reach more than 39%.Moreover, it has stable performance and long service life.However, this kind of battery is expensive, and the average price per watt can be dozens of times higher than that of polysilicon solar cells, so it is not the mainstream of civil use.
Because of its direct energy gap and high light absorption coefficient, as well as its good resistance to reflection damage and insensitivity to temperature changes, it is suitable for application in three main fields, namely, thermophotovoltaics TRV, concentrator system and space.
Since August 2007, gallium arsenide batteries have changed from satellite use to concentratingSolar power stationScale application.Gallium arsenide high-efficiency concentrating cells are proving to be an effective way to build solar power plants at low cost in foreign countries.
(2) Ⅱ - Ⅵ compound solar cells
Group Ⅱ - Ⅵ compound solar cells include cadmium telluride thin film cells andCopper Indium Gallium SeleniumThin film battery.
The CdTe battery has a direct energy gap of 1.45eV, which is just within the energy gap range of an ideal solar cell.In addition, it has a high light absorption coefficient.It becomes one of the ideal solar cell materials that can obtain high efficiency.In addition, it can be made by a variety of rapid film forming technologies. Due to the ease of modular production, it has a good commercial performance in recent years. CdTe/glass has been used for large-area roof materials.However, cadmium pollution is a hidden danger in the development of the thin film battery.However, the United States and Germany have implemented the CdTe solar cell recycling and regeneration mechanism to inject positive force into the market.Since the production process of the battery takes only a few minutes and is easy to produce in batches, the United States is quite optimistic about the market prospect.It is believed that the share of amorphous silicon solar cells may exceed in the future.
Solar cells
Copper, indium, gallium and selenium have a very wide light absorption range, and have good stability in outdoor environment.Because of its high conversion efficiency and low material manufacturing cost, it is considered as one of the most promising thin-film batteries in the future.In terms of conversion efficiency, with the help of the concentrator, the current conversion efficiency can reach about 30%, and the highest level can reach 19.5% under the standard environmental test, which is comparable to the monocrystalline silicon solar cells.In addition to being suitable for large-scale surface applications, Cu (InGa) Se2 solar cells also have the ability to resist radiation damage, so they also have potential applications in the space field.After 30 years of development, the popularity of CIGS batteries is still not high.In the stage of small-scale mass production, the cost advantage expected by the world is not clearly seen.Therefore, how to make mass production technology of solar cells mature and significantly reduce manufacturing costs is the subject of future efforts.Another development direction is to develop CIGS technology with relatively wide energy gap (greater than 1.5eV) without causing efficiency loss.Developing a low-temperature manufacturing process that can produce high-quality CIGS films is also a key point to reduce manufacturing costs.Attracted by the market potential of low material cost and high module efficiency, in recent years, in addition to Shell Solar, Wrth Solar, Show Shell, ZSW, etc., which continue to invest in research and development, even Honda has followed up production.The hidden danger of the development of CIGS solar cells is that the reserves of In and Ga are limited. With the competing use of other semiconductor and optoelectronic industries, they may face the same problem of insufficient silicon materials at present.At the same time, the complex manufacturing process and high investment cost restrict the market growth;CdS has the disadvantage of potential toxicity, which limits the market development.
Thin film solar cells on flexible substrates
The research of Toledo University in the field of flexible substrate amorphous silicon solar cells is in the leading position in the world. The initial efficiency of its single junction amorphous silicon germanium battery laboratory has reached 13%. Their technical team has participated in the establishment of MWOE and Xunlight companies, and is actively planning for greater production capacity.
Japan also leads the world in the research of flexible substrate solar cells.In Japan, Sharp, Sanyo, TDK and Fuji have invested a lot of manpower and material resources in the development of amorphous silicon solar cells on flexible substrates, and have built several megawatt flexible polyester film battery production lines.
SanyoThe company was the first to use flexible substrate amorphous solar cells as energy in unmanned solar aircraft, completing the flight across the Americas, showing the huge potential of flexible amorphous thin film solar cells as aircraft energy.The amorphous silicon solar cells prepared by Sharp Company and TDK Company on polyester film can now produce modules with an area of 286cm2, and the efficiency has reached 8.1%, while the efficiency of small area batteries has reached 11.1%.Fuji a-Si/a-SiGeLaminated batteryThe stable efficiency reached 9%. A factory was established in Kumamoto, Japan. The output of amorphous silicon cells on plastic substrate reached 15MW in 2006.
The EU has cooperated with several research institutions and organizations in its member countries, including Neuchatel University, VHF technologies, Roth&Rau, to carry out joint research on flexible batteries on polyester film substrates. At present, small batch production lines have been realized.On October 1, 2005, the EU launched the 'FLEXCELLENCE' project, which lasts for three years. The goal is to develop the equipment and process for the roll to roll production of high-efficiency thin film battery modules, build a flexible battery production line of more than 50 megawatts, and hope to control the production cost at 0.5 euros per watt.According to the report in 2007, the laboratory efficiency of amorphous silicon laminated battery on polyester film substrate at Neuchatel University has reached 10.8%, and the annual capacity of VHF technologies is 25MW.
The research progress of thin film batteries on flexible substrates in China is relatively slow.Harbin chrona developed flexibility in the mid-1990spolyimideThe initial efficiency of amorphous silicon single junction thin film battery on the substrate is 4.63%,Power weight ratio231.5W/kg, but little progress has been made since then.In recent years, Nankai University has made some progress in the research of amorphous silicon thin film batteries on flexible substrates. They obtained single junction thin film batteries on 0.115cm2 polyimide substrates with an initial efficiency of 4.84% and a power weight ratio of 341W/kg.
In terms of industrialization of flexible substrate batteries, Tianjin Jinneng Battery Co., Ltd. is currently building a 6MW amorphous silicon flexible battery production line, and a 30MW production line has begun project demonstration. Xinjiang Tianfu Photovoltaic Display Co., Ltd. is building a 1MW amorphous silicon flexible battery production line, and is preparing to build 8MW in the future.As the equipment and technology of these two companies are imported from abroad, the cost of batteries is expected to be high.In general, China currently has the technical basis for the development of amorphous silicon thin film batteries, but the research on flexible substrates is still in its infancy, and there is a big gap between China and foreign countries.[3]
Solar energy use
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Satellite solar panel
1. Solar cells of user's solar power supply
[1] Small power supplies ranging from 10-100W are used for military and civilian life in remote areas without power, such as plateau, island, pastoral area, border post, etc., such as lighting, television, radio recorder, etc;
[2] 3-5 KW family roof grid connected power generation system;
[3] Photovoltaic water pump: solve drinking and irrigation of deep water wells in areas without electricity.
2. Transportation
Such as beacon lights, traffic/railway signal lights, traffic warning/sign lights, street lightsHigh altitude obstacle light, highway/railway radio telephone booth, unattended road shift power supply, etc.
Solar street lamp
Satellite solar panel
3. Communication/communication field
Solar unattended microwave relay station, satellite, optical cable maintenance station, broadcast/communication/paging power system;Rural carrier telephonePV systemSmall communication machine, soldier GPS power supply, etc.
4. Petroleum, marine and meteorological fields
Cathodic protection solar power supply system for oil pipeline and reservoir gate, domestic and emergency power supply for oil drilling platform, marine detection equipment, meteorological/hydrological observation equipment, etc
Solar street lamp
5. Power supply of household lamps
Such as garden light, street light, portable light, camping light, climbing light, fishing light, black light, tapping light, energy-saving light, etc.
Solar cell clothing
6. Photovoltaic power station
10KW-50MW independent photovoltaic power station, wind solar (diesel) complementary power station, charging stations of various large parking plants, etc.
7. Clothing
Solar clothing, space suits, etc.
Latest progress
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South China University of Technologyhigh polymerPhotoelectric materialWith the research team of the Device Research Institute, on the basis of the water/alcohol soluble polymer solar cell interface control materials and technology, which is the first of its kind and has independent intellectual property rights, through collaborative innovation, the polymer solar cell with an inverted structure has achieved an energy conversion efficiency of 9.214%, refreshing the world's best level of energy conversion efficiency of single junction polymer heterojunction solar cells.This achievement was also recently selected as one of the "Top Ten Scientific Advances in China" in 2012.
This achievement is made byNational Science Fund for Distinguished Young ScholarsWinners: Professor Wu Hongbin andAcademician of CASProfessor Cao Yong's research team of polymer optoelectronic materials and devices completed their invention of an efficient and novel inverted structure polymer solar cell, which achieved 9.214% energy conversion efficiency, and this efficiency wasNational PV Quality Inspection CenterIndependent certification of.The research results were published in the internationally famous academic journal NaturePho? Nics (Natural Photonics) and selected as the research highlights in this issue.[4]
