Since the French scientist Becqure discovered the photovoltaic effect in 1893, until 1954, scientists at Bell Laboratories in the United States successfully developed a crystalline silicon solar cell with a P-N junction as the basic structure, and took the lead in space satellites. Effectively apply in technology. So far, photovoltaic power generation has made considerable progress from theory to actual production and application technology. Therefore, the photo-electric conversion of solar energy is usually called solar photovoltaic power generation. Photovoltaic technology has developed into a huge subject system today, and it has been created at the same time. An emerging industry chain. It can directly convert sunlight radiation into electrical energy, using a silicon-based semiconductor device. When we use two P (N)-type semiconductors and N (P)-type semiconductors with different conductivity properties as basic materials; a thinner layer of N-type material is compounded on the surface of the P-type substrate by diffusion method, and After forming an interpenetrating PN junction at the contact interface between the two, the compounded crystalline silicon semiconductor material, when the N surface is irradiated by sunlight, the atoms in the semiconductor silicon material are excited by high-energy photons. The space charge distribution is naturally formed on both sides of the P-N junction interface, and under the action of this space charge region; hole-electron pairs are generated in the P and N regions on both sides of the so-called PN junction, and the electrons are driven to the N Area; holes are transferred to the P area; thereby generating a photoelectromotive force at both ends of the PN junction, forming a charged electric field. At this time, if the lead-out electrodes on both sides of the P-N junction are connected to the load resistors with lead wires, current will flow through and energy will be transferred to the load resistors at the same time. This is the basic working principle of photovoltaic cells converting high-energy solar radiation into electrical energy.
The optimal load resistance value of each group of solar cells (the so-called photovoltaic conversion efficiency) is determined by factors such as the quality of the battery material, the area of the solar panel, the solar radiation energy (short-wavelength band) photon intensity, and the temperature of the solar panel. Decide. Under the full-band spectrum of sunlight, the photoelectric conversion efficiency of each group of solar cells has a negative temperature coefficient: short-circuit current (short-circuit the solar cell, the resulting current is a short-circuit current) will increase with the increase in light intensity A slight increase, while the open circuit voltage (the voltage when the sum of short-circuit current and forward current is 0 is called “open circuit voltage”) has a significant decrease with the increase of light intensity. In other words, the photoelectric conversion efficiency of each solar cell, that is, the output power, will decrease as the temperature of the PN junction increases and the open circuit voltage decreases. Therefore, during the engineering design of the solar light-to-electric conversion system, how to reduce the operating temperature of the solar panel while other factors remain unchanged; in other words, how to keep the solar panel stable at the optimal operating temperature for a long time Power generation is also a technical problem that cannot be ignored.
According to the maturity of solar cell production technology, solar cells are from the original single–first-generation monocrystalline silicon and polycrystalline silicon series of crystalline silicon cells; the second-generation thin-film solar cells of amorphous silicon [including: copper Indium selenium (CIS), cadmium telluride (CdTe), double-junction stacked and three-junction stacked solar cells, gallium arsenide solar cells and nano-titanium oxide dye-sensitized solar cells, etc.]; the third generation of new concept organic cells (Including: thermal photovoltaic cells, superlattice solar cells of quantum wells and quantum dots, intermediate solar cells, up-conversion solar cells, down-conversion solar cells, hot carrier solar cells: and collision ionization solar cells, etc. New batteries, etc.), has formed a complete product series. At present, the first-generation crystalline silicon solar cells have entered the stage of large-scale industrial production: the second-generation solar cells are in the early stages of industrialization, and some types have just achieved mass production, and the technological maturity needs to be further improved: the third-generation high-eAccording to the maturity of solar cell production technology, solar cells start from the first-generation single-crystal silicon and polycrystalline silicon series of crystalline silicon cells with a single species; the second-generation thin-film solar cells that extend from amorphous silicon [including: copper indium selenium (CIS), cadmium telluride (CdTe), double-junction stacked and triple-junction stacked solar cells, gallium arsenide solar cells and nano-titanium oxide dye-sensitized solar cells, etc.); the third generation of new concept organic cells (including : Thermal photovoltaic cells, quantum wells and quantum dot superlattice solar cells, intermediate zone solar cells, up-conversion solar cells, down-conversion solar cells, hot-carrier solar cells: and a series of new batteries such as collision ionization solar cells Etc.), a complete product series has been formed. At present, the first-generation crystalline silicon solar cells have entered the stage of large-scale industrial production: the second-generation solar cells are in the early stages of industrialization, and some types have just achieved mass production, and the technological maturity needs to be further improved: the third-generation high-efficiency Most of the solar cells are still in the conceptual and theoretical design stage. The industrialization of this generation of high-efficiency cells still needs to be further explored by scientists from theory to practice.
The laboratory efficiency of monocrystalline silicon solar cell photoelectric conversion, from 6% in the 1950s to the high record of 24.7% created by the Australian Chinese business scientist Zhao Jianhua at the University of New South Wales in Australia in 1997, has not yet been broken. : The laboratory efficiency of polycrystalline silicon batteries also reached 20.3%; the efficiency of crystalline silicon commercial batteries was increased to 13%-17% on average; the laboratory efficiency of amorphous silicon thin-film batteries reached about 13%: the efficiency of commercial batteries was also common Increase to 8%-12%. Cadmium telluride (CrTe) reached 16.4% and copper steel selenium (CIS) reached 19.5%.
Considering from the global storage of solar cell production materials, because the reserves of silicon on the earth are very abundant; therefore, from the perspective of large-scale production and application, for a long time in the future, crystalline silicon solar cells will be the mainstream of the market. The general trend is beyond doubt. Although other solar cells have their own unique advantages in terms of photoelectric conversion efficiency or other physical characteristics of the cell, they face many constraints. Whether they can surpass silicon-based cells to form new ultra-mainstream products in the future, it is still to be said. Too early.