Abstract: Faced with the dual pressures of limited conventional energy and serious environmental damage, human beings have become more and more social and environmental problems worthy of attention. In recent years, the photovoltaic market has developed rapidly and achieved gratifying results. This paper introduces the principle and development of solar cells, as well as various new solar cells, and compares the conversion efficiency and development prospects of various solar cells. Keywords: solar cell; Principle; Development; prospect
1. Introduction
Due to the continuous demand for renewable energy, people are committed to developing new energy sources. The energy that the sun shines on the earth's surface in 40 minutes can be used 1 year at the current global energy consumption rate. The rational use of solar energy will be a long-term development strategy for solving energy problems and one of the most attractive research hotspots. This paper introduces the principle and development of solar cells, as well as various new solar cells, and compares the conversion efficiency and development prospects of various solar cells.
2. The principle of solar cell 1
Solar cells are semiconductor devices that can effectively absorb solar radiation energy and convert it into electric energy. Because they use the photovoltaic effect of various barriers, they are also called photovoltaic cells, and their core is semiconductors that can release electrons. The most commonly used semiconductor material is silicon. The crust is rich in silicon, which can be said to be inexhaustible.
When the sun shines on the surface of the semiconductor, the valence electrons of the atoms in the N and P regions in the semiconductor are excited by solar photons and obtained by optical radiation.
For energy exceeding the forbidden band width, for example, separation.
* * * The valence bond is excited from the valence band to the conduction band,
Therefore, many are generated inside the semiconductor material.
Electron-hole pair in nonequilibrium state. this
Some electrons and holes are excited by light or freedom.
Collisions or recombination in semiconductors return to a flat state.
Equilibrium state. Wherein the composite process is not presented to the outside.
Conductive effect belongs to the self-energy of solar cells.
Dynamic loss part. Less photo-excited carriers
Carriers can move to the pn junction region and pass through.
Traction of minority carriers by P-N pairing
Use and drift to the other side of the area, and externally form and.
Photogenerated electric field in the opposite direction to the electric field of pn junction barrier. Once the external circuit is connected, there can be electric energy output. When many such small solar photovoltaic cells are combined in series and parallel to form a photovoltaic cell module, they will output enough electric energy under the action of solar energy.
It is very important that the semiconductor materials used to manufacture solar cells have appropriate band gaps. Semiconductors with different band gaps can only absorb a part of solar radiation energy to produce electron-hole pairs. The smaller the band gap width, the larger the available part of the absorbed solar spectrum.
At the same time, waste energy near the peak of the solar spectrum.
The bigger it is. It can be seen that only by selecting semiconductor materials with appropriate band gap width can the solar spectrum be used more effectively. Because the light absorption efficiency of the direct migration type semiconductor is higher than that of the indirect migration type semiconductor, the direct migration type semiconductor is preferred.
Solar photovoltaic power generation system is a new type of power generation system, which uses the photovoltaic effect of semiconductor materials of solar cells to directly convert solar radiation energy into electric energy. There are two modes of independent operation and grid-connected operation. Independent photovoltaic power generation system needs storage battery as energy storage device, which is mainly used in remote areas without power grid and scattered population areas, and the whole system cost is very high; In areas with public power grids, grid-connected photovoltaic power generation system can not only greatly reduce the cost, but also have higher power generation efficiency and better environmental protection performance.
Photovoltaic panel assembly is a kind of power generation device that collects heat and converts light energy into direct current under sunlight irradiation. It consists of thin solid photovoltaic cells made almost entirely of semiconductor materials (such as silicon). Because there are no moving parts, it can run for a long time without any loss. Simple photovoltaic cells can provide energy for watches and computers, while more complex photovoltaic systems can provide lighting for houses and power for power grids.
Photovoltaic panel modules can be made into different shapes, and the modules can generate more electricity when connected. In recent years, photovoltaic panels have been used on roofs and building surfaces, and even as windows.
A part of a skylight or shading device. These photovoltaic facilities are usually called photovoltaic systems attached to buildings.
What is solar photovoltaic technology?
The sun is a natural energy source. Every living thing on the earth has the ability to function, and even its survival is attributed to the energy directly or indirectly from the sun.
Our earth is nearly 1 100 million miles from the sun. The radiation energy it intercepts is incredibly low, about three parts per million. Even with such a small amount of energy,
In fact, it is more than the current power generation capacity in the world100000 times! At present, the whole world, especially industrialized countries, is beginning to feel energy shortage, so people are turning to it.
Solar energy solves the energy crisis.
Solar photovoltaic
Solar energy can be supplied infinitely every day, and the quantity is huge. If used in large power plants, it will reduce the greenhouse effect. Some energy experts and environmental experts believe that the thermal impact ratio of solar energy is not enough to meet the future energy demand of mankind. Some experts believe that solar power will eventually account for 20% of electricity supply. Solar energy is a kind of radiant energy, and solar power generation means that with the help of any other mechanical parts, the energy in the light is obtained through the electrons of semiconductor devices, thus generating electric energy. Made of this semiconductor. Its main material is silicon, and there are some other alloys. High-purity silicon used to make solar cells needs special purification treatment. Solar cells can convert light energy into electric energy as long as they are irradiated by sunlight or light.
10~20% electricity. ordinary
Can be converted into electric energy, generally covered with a film to prevent light reflection, so that the surface of solar panels is purple. Its working principle is based on semiconductor PN.
When illuminated, the charge distribution in the object changes, resulting in the effects of electromotive force and current. When sunlight or other light irradiates the semiconductor PN junction, a voltage (called photovoltaic voltage) will appear on both sides of the PN junction. This phenomenon is the famous photovoltaic effect. If the PN junction is short-circuited, a current will be generated.
Solar cells can be installed in unused spaces, such as roofs, with no noise, long service life and little need to be adjusted once installed. Now, as long as solar cells are installed on the roof, we can achieve self-sufficiency in household electricity. Now the sun
A lightweight solar cell that can be worn on the body. At present, the utilization of solar energy has a huge development space.
Related technologies may make a breakthrough in a short time. Many developed countries have regarded it as an important part of energy strategy. Take crystal as an example to describe the process of photovoltaic power generation. P-type crystalline silicon can be doped with phosphorus to obtain N-type silicon, forming
Pn junction When light is irradiate on that solar cell,
Example of solar photovoltaic power generation system
On the surface, some photons are absorbed by silicon materials; Photon energy is transferred to silicon atoms, which makes electrons migrate and become free electrons to gather on both sides of P-N junction, forming potential difference. When the external circuit is turned on, under the action of this voltage,
The process of energy.
Since 1954, great progress has been made in solar photovoltaic power generation. But it is much slower than the development of computer and optical fiber communication. The reason may be that people's pursuit of information is particularly strong, and conventional energy can also meet human demand for energy.
1973 oil crisis and 90
The environmental pollution in 1990s greatly promoted the development of solar photovoltaic power generation. Its development process is briefly described as follows:
1839
, namely "photovoltaic effect". 1876 1883 made the first "selenium photovoltaic cell" as a sensitive device. Schottky put forward the "photovoltaic effect" theory of Cu2O barrier in 1930. In the same year, Langer first
Schematic diagram of lightning protection for grid-connected photovoltaic power generation system equipment
It has been proposed to manufacture "solar cells" with "photovoltaic effect" to convert solar energy into electric energy. 193 1 year Bruno
Immerse the copper compound and the silver selenium electrode in the electrolyte, and start the motor in the sun. 1932 Audubot and Stora made their first work. "
Cadmium sulfide "solar cell. 194 1 year 1954
It's only 6% In the same year, Vekker first discovered that gallium arsenide has photovoltaic effect, and deposited cadmium sulfide thin film on glass to make the first thin film solar cell. 1955
In the same year, the first photoelectric beacon light came out. American RCA studies gallium arsenide solar cells. The efficiency of 1957 silicon solar cell reaches 8%.
single crystalline silicon solar cell
1958, solar cells were first used in space, equipped with the power supply of American pioneer 1 satellite. 1959 The first efficiency reaches 5%. 1960 silicon solar cells are connected to the grid for the first time. 1962
The photoelectric conversion efficiency of GaAs solar cells reaches 65438 03%. The efficiency of 1969 thin-film cadmium sulfide solar cell reaches 8%. 197216%.1972 American aerospace company's back field battery came out. 1973
The efficiency of GaAs solar cells reaches 15%. 1974, COMSAT Institute proposed a non-reflective textured battery, and the efficiency of silicon solar cells reached 18%. The efficiency of 1975 is 6%~%. 1976
The annual efficiency of polysilicon solar cells reaches 10%. 1978, the United States built 100kWp solar ground photovoltaic power station. 1980 20%, gallium arsenide battery 22.5%, polysilicon battery 14.5%, cadmium sulfide battery 9. 15%. 1983 made in America 1MWp.
Photovoltaic power station; Metallurgical silicon (epitaxy)
The battery efficiency reached 1 1.8%. 1986, a 6.5 MW photovoltaic power station was built in the United States. 1990 "2000 photovoltaic roofs plan", in which 3~5kWp photovoltaic cells are installed on the roofs of each family. 1995 high-efficiency concentrating GaAs solar cells have an efficiency of 32%.
1997 the United States proposed "planning" in
Before 20 10, there were 100000 households, each household was installed with 3~5kWp power supply, and the electric meter was installed backwards; When there is no sun, the power grid supplies electricity to the home, and the electricity meter is turning. Families only need to pay the "net electricity bill".
1997 new sunshine plan proposes to produce 4.3 billion Wp photovoltaic cells by 20 10. From 1997 to 20 10, 3.7 billion Wp photovoltaic cells were produced.
1998 monocrystalline silicon photovoltaic cell efficiency reaches 25%. Dutch government photoelectric conversion efficiency
η% is an important factor to evaluate the quality of solar cells. At present: laboratory η ≈ 24%, industrialization: η ≈ 15%. Unit cell voltage
V: 0.4V-0.6V is determined by the physical properties of the material.
Filling factor FF%
Important factors for evaluating the load capacity of solar cells. FF=(Im×Vm)/(Isc×Voc) where: isc- short circuit current, Voc- open circuit voltage, im- optimal working current, Vm- optimal working voltage;
Standard light intensity
AM 1.5 light intensity, 1000W/m2, t = 25℃;
Effect of temperature on battery performance
For example, under standard conditions, the light intensity of AM 1.5, and at t=25℃, the output power of a battery panel is 100Wp. If the battery temperature rises to 45℃, the output power of the battery panel will be less than 100Wp.
5. Conclusion
Solar photovoltaic power generation is the best way to use solar energy. At present, the transition from the first generation solar cell based on silicon wafer technology to the second generation semiconductor solar cell based on semiconductor thin film technology is in progress. The conversion efficiency of the first generation solar cells is 1 1%~ 15%, but the cost is too high. The cost of the second generation solar cells is greatly reduced, but the conversion efficiency is only 6%~8%. In order to further improve the efficiency, the third generation solar cell based on thin film technology is developed, and its conversion efficiency will be several times that of the first and second generation solar cells. Its appearance will turn a new page in the history of solar energy utilization.
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