Among the silicon series solar cells, monocrystalline silicon solar cells have the highest conversion efficiency and the most mature technology. High-performance monocrystalline silicon cells are based on high-quality monocrystalline silicon materials and related heat-generating processing techniques. Monocrystalline silicon battery technology is almost mature. In battery production, surface texturing, emitter zone passivation, zoned doping and other technologies are generally used. The developed batteries mainly include planar monocrystalline silicon cells and grooved monocrystalline silicon cells. The improvement of conversion efficiency mainly relies on the treatment of the surface microstructure of single crystal silicon and the zoned doping process. In this regard, the Fraunhofer Institutefor solar energy systems in Freiburg, Germany, remains a world leader. The institute uses photolithography technology to texture the surface of the battery into an inverted pyramid structure. And put a 13nm on the surface. A thick layer of oxide passivation combined with two layers of anti-reflective coating. The width-to-height ratio of the door is increased through an improved electroplating process: the battery conversion efficiency obtained above exceeds 23%, with a maximum value of 23.3%. The large-area (225 cm2) monocrystalline solar cell prepared by Kyocera has a conversion efficiency of 19.44%. Beijing Solar Energy Research Institute in China is also actively carrying out research and development of high-efficiency crystalline silicon solar cells. High efficiency monocrystalline silicon cell (2cm) The conversion efficiency of crystalline silicon cellwith grooved buried gate electrode (5 cm
The conversion efficiency of monocrystalline silicon solar cells is undoubtedly the highest and still occupies a dominant position in large-scale applications and industrial production However, due to the price of monocrystalline silicon materials and the corresponding bulkiness, in battery manufacturing processes, the cost and price of monocrystalline silicon remains high, and it is very difficult to significantly reduce its cost. To save high-quality materials and find alternatives to monocrystalline silicon solar cells, thin-film solar cells have been developed, including polycrystalline silicon thin-film solar cells and amorphous silicon thin-film solar cells. are typical representatives Usually, crystalline silicon solar cells are manufactured on tr.high-quality silicon reeds with a thickness of 350-450 μm, sawn from drawn or cast silicon ingots. Therefore, more silicon is actually consumed. In order to save materials, people have been depositing polysilicon films on cheap substrates since the mid-1970s. However, due to the grain size of the grown silicon film, valuable solar cells have not been produced. produced. In order to obtain thin films with large grain sizes, researchers have never stopped researching and have proposed numerous methods. Chemical vapor deposition methods are often used to prepare polycrystalline silicon thin-film batteries, including low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD) processes. . Additionally, liquid phase epitaxy (LPPE) and sputter deposition methodse can also be used to prepare thin film polycrystalline silicon cells.
Chemical vapor deposition mainly uses SiH2Cl2, SiHCl3, Sicl4 or SiH4 as the reaction gas. It reacts under a certain protective atmosphere to generate silicon atoms and deposits them on a heated substrate. The substrate material is generally Si., SiO2, Si3N4, etc. However, research has shown that on substrates without silicon, it is difficult to form larger grains on the surface and it is easy to form gaps between grains. The way to solve this problem is to first use LPCVD to deposit a thin layer of amorphous silicon on the substrate, then anneal this amorphous silicon layer to obtain larger crystal grains, and then deposit the seed crystal on this layer by depositing thick polysilicon films. , therefore, the recrystallization technology is without anya doubt a very important link. The main technologies used are the solid phase crystallization method and the midzone melt recrystallization method. In addition to the recrystallization process, polycrystalline silicon thin film cells also adopt almost all monocrystalline silicon solar cell preparation technologies. The conversion efficiency of the solar cells thus produced is significantly improved. The Freiburg Solar Energy Research Institute in Germany uses district recrystallization technology to produce polycrystalline silicon cells on FZ Si substrates with a conversion efficiency of 19%. The Japanese company Mitsubishi Corporation uses this method to prepare cells with a yield of 16.42%.
The principle of liquid phase epitaxy (LPE) method is to melt the silicon in the matrix and lower the ttemperature to precipitate the silicon film. The efficiency of the battery produced by Astropower Company in the United States from LPE reaches 12.2%. Chen Zheliang of China Optoelectronics Development Technology Center used liquid phase epitaxy to grow silicon grains on metallurgical-grade silicon wafers and designed a new type of solar cell similar to crystalline silicon thin-film solar cells , called a “silicon grain” solar energy battery, but there are no performance reports there.
Since polycrystalline silicon thin film cells use much less silicon than monocrystalline silicon, there is no efficiency degradation problem and they can be produced on materials cheap substrate, their cost is much lower than that of monocrystalline silicon cells. The efficiency is higher than that of cells withthin layers of amorphous silicon. Therefore, polycrystalline silicon thin-film cells will soon dominate the solar energy market. The two key issues in the development of solar cells are: improving conversion efficiency and reducing costs. Due to the low cost of amorphous silicon thin-film solar cells and their ease of mass production, they have generally attracted public attention and developed rapidly. In fact, by the early 1970s, Carlson and others had already begun the development of amorphous silicon. cells. In recent years, its research and development work has developed rapidly in 2008, and many companies in the world produce this type of battery products.
Although amorphous silicon is a good battery material as a solar material, its optical band gap is 1.7 eV, which makes the material itselfme insensitive to the long wavelength region of the solar radiation spectrum. conversion efficiency of solar cells to amorphous silicon. In addition, its photoelectric efficiency will attenuate as the lighting duration continues, so-called light-induced decay S-W effect, making the battery performance unstable. One way to solve these problems is to prepare tandem solar cells. Tandem solar cells are fabricated by depositing one or more P-i-n sub-cells onto the prepared p,i,n layer single junction solar cells. The key issues for laminated solar cells to improve the conversion efficiency and solve the instability of single junction cells are as follows: ① It combines materials with different bandgap widths to improve the spectrum response range ② The layer i of the upper cell is thin; , and lightingntensity of the generated electric field does not change much, ensuring that the photogenerated carriers in layer i are extracted ③ The carriers generated by the lower cell are approximately; It is half that of a single cell, and the Light-induced degradation effect is reduced ④ Each sub-cell of a laminated solar cell is connected in series;
There are many methods to prepare amorphous silicon thin film solar cells, including reactive sputtering, PECVD, LPCVD, etc. The gas of the reaction raw material is SiH4 diluted with H2, and the substrates are mainly glass and stainless steel. sheets, the produced amorphous silicon thin film can be used to produce single junction cells and tandem solar cells through different battery processes. Research on amorphous silicon solar cells has achieved two major advances: first,he conversion efficiency of amorphous silicon solar cells with three-layer structure reached 13%, setting a new record. Secondly, the annual production capacity of three-layer solar cells has reached; reached 5 MW. The highest conversion efficiency of single-junction solar cells produced by United Solar Energy Corporation (VSSC) is 9.3%, and the highest conversion efficiency of three-layer three-bandgap solar cells is 13 %. >Highest conversion efficiency mentioned above. Efficiency is obtained on a battery with a small surface area (0.25 cm2). It has been reported in the literature that the conversion efficiency of single junction amorphous silicon solar cells exceeds 12.5%. Japan's Academia Sinica adopted a series of new measures, and the conversion efficiency of the produced amorphous silicon cells was 13.2%. There isn't a lot of researchnational amorphous silicon thin film cells, especially laminated solar cells Geng Xinhua of Nankai University and others used industrial materials and aluminum back electrodes to prepare a - with an area of 20X20 cm2 and a conversion efficiency of 8.28. %. Stacked Si/a-Si solar cells.
Amorphous silicon solar cells have great potential due to their high conversion efficiency, low cost and light weight. But at the same time, its low stability directly affects its practical application. If the stability problem and the conversion rate problem can be further solved, then large amorphous silicon solar cells will undoubtedly be one of the main development products of solar cells. In order to find alternatives to monocrystalline silicon cells, people have not only developed solar cells tothin layers of polycrystalline silicon and amorphous silicon, but also continue to develop solar cells made of other materials. These mainly include gallium III-V arsenide compounds, cadmium sulfide, cadmium sulfide and copper-indium-selenium thin film batteries. Among the batteries mentioned above, although the efficiency of cadmium sulfide and cadmium telluride polycrystalline thin film solar cells is higher than that of amorphous silicon thin film solar cells, the cost is lower than that of monocrystalline silicon cells and they are easy to use. mass produce, but since cadmium is very toxic, it will cause serious environmental pollution and therefore is not the most ideal substitute for crystalline silicon solar cells.
Gallium III-V arsenide compounds and Cu selenide thin film batteriesIndium and indium have received wide attention due to their high conversion efficiency. GaAs is a III-V compound semiconductor material with an energy gap of 1.4eV, which exactly corresponds to the high absorption value of sunlight. So it is an ideal battery material. The preparation of III-V compound thin film batteries such as GaAs mainly uses MOVPE and LPE technologies. The preparation of GaAs thin film batteries by the MOVPE method is affected by many parameters such as substrate dislocation, reaction pressure, III-V ratio and. total flow.
Except GaAs, other II-V compounds such as Gasb, GaInP and other battery materials have also been developed. The conversion efficiency of the GaAs solar cell produced by the Freiburg Solar Energy Research Institute in Germany in 1998 was 24.2%, a European record. Bat conversion efficiencyrie GaInP prepared for the first time was 14.7%. See Table 2. In addition, the institute also uses a stacked structure to prepare GaAs and Gasb batteries. This battery is a stack of two independent batteries, with GaAs as the upper battery and the lower battery using Gasb. The resulting battery efficiency reaches 31.1%.
Copper indium selenium CuInSe2 is called CIC. The energy of CIS material is reduced to 1.leV, suitable for photoelectric conversion of sunlight. Additionally, CIS thin-film solar cells do not exhibit light-induced degradation issues. Therefore, CIS has also attracted people's attention as a material for thin-film solar cells with high conversion efficiency.
The preparation of CIS battery thin films mainly includes vacuum evaporation method and selenization method. The evaporation methodou vacuum uses separate evaporation sources to evaporate copper, indium and selenium. The selenization method uses a stacked H2Se film for selenization. However, this method is difficult to obtain CIS with uniform composition. CIS thin film batteries have grown from an initial conversion efficiency of 8% in the 1980s to around 15%. The photoelectric conversion efficiency of the gallium-doped CIS cell developed by Japan's Matsushita Electric Industrial Co., Ltd. is 15.3% (area 1 cm2). In 1995, the American Renewable Energy Research Laboratory developed a conversion efficiency of 17.1% CIS solar cell, which is the highest conversion efficiency of this cell in the world so far. The conversion efficiency of CIS cells is expected to reach 20% by 2000, equivalent to that of polycrystalline silicon solar cells.in.
As a semiconductor material for solar cells, CIS has the advantages of low price, good performance and simple process, and will become an important direction for the development of cells solar in the future. The only problem lies in the source of the materials. Indium and selenium being relatively rare elements, the development of this type of battery is necessarily limited. Replacing inorganic materials with polymers in solar cells is a research direction in solar cell preparation that has only just begun. The principle is to use the different redox potentials of different redox polymers to make multilayer composites on the surface of conductive materials (electrodes) in order to create a unidirectional conductive device similar to an inorganic P-N junction. The inner layer of an electrode is modified by a polymer with a potential ofe lower reduction, and the outer polymer has a higher reduction potential. The direction of electron transfer can only be transferred from the inner layer to the outer layer; is just the opposite, and the first The reduction potentials of the two polymers on each electrode are higher than those of the last two polymers. When two modified electrodes are placed in the electrolysis wave containing a photosensitizer. The electrons generated after the photosensitizer absorbs light are transferred to the electrode with a lower reduction potential. Electrons accumulated on the electrode with lower reduction potential cannot be transferred to the external polymer and can only be returned to electrolysis via an external circuit. an electrode with a higher reduction potential, so the photocurrent is generated in the external circuit.
Due to the advantages of organic materials such as flexibility, ease of production, wide sources of materials and low cost,It is very important to use solar energy on a large scale and provide cheap electricity. However, research into using organic materials to prepare solar cells is only just beginning. Neither the lifespan nor the efficiency of the cells can be compared to that of inorganic materials, especially silicon cells. Whether it can become a product of practical importance remains to be studied and explored in more detail. Silicon-based solar cells are undoubtedly the most mature among solar cells, but due to their high cost, they are far from meeting the requirements for large-scale promotion and application. To this end, people have constantly explored aspects such as technology, new materials and thin-film batteries. Among them, the new solar cellss chemical nano-TiO2 crystals have attracted the attention of domestic and foreign scientists.
Since Swiss professor Gratzel successfully developed large nano-TiO2 chemical solar cells, some national units are also carrying out research in this field. Nanocrystalline chemical solar cells (NPC cells for short) are formed by modifying and assembling one narrow bandgap semiconductor material onto another narrow bandgap semiconductor material. The narrow bandgap semiconductor material uses organic compounds such as the transition metal Ru and Os. The semiconductor materials are nanopolycrystalline TiO2 and made into electrodes. Additionally, NPC batteries also use appropriate redox electrolytes. The working principle of nanocrystalline TiO2: dye molecules absorb solar energy and enter the excited state. The excited state is unstablethe and electrons are rapidly injected into the adjacent conduction band of TiO2. The electrons lost in the dye are quickly compensated by the electrolyte and. Enter the TiO2 conduction band. The electricity in the film finally enters the conductive film and then generates photocurrent through the outer loop.
The advantages of TiO2 nanocrystalline solar cells are low cost, simple process and stable performance. Its photoelectric efficiency is stable at more than 10%, and its production cost is only 1/5 to 1/10 of that of silicon solar cells. The lifespan can reach more than 20 years. However, as the research and development of this type of battery has just started, it is expected that it will gradually enter the market in the near future.
Principle of energy production by silicon solar cells
Silicon is a semiconductor material. THEprinciple of energy production by solar cells mainly uses the photoelectric effect of this semiconductor. semiconductor molecules The structure is as follows: the positive charge represents the silicon atom and the negative charge represents the four electrons surrounding the silicon atom. The ** represents the incorporated boron atom. Therefore, there are only three electrons around the element boron, so such blue holes can become very unstable because they have no electrons and can easily neutralize them to form a p-. semiconductor type.
What is the difference between perovskite solar cells and crystalline silicon solar cells?
The production of silicon solar cells mainly relies on semiconductor materials. Its working principle is to use photoelectric materials to absorb light energy and then produce photo conversion reactions.oelectric.
When other impurities are added to the silicon crystal, such as boron, which is relatively stable at room temperature and can interact with nitrogen, carbon and silicon, the boron also reacts with many metals and metal oxides at elevated temperatures. temperatures to form?
:Usual crystalline silicon solar cellsThe pool is made on high-quality silicon wafers with a thickness of 350-450 µm, sawn from drawn or cast silicon ingots.
TOPCon cells and heterojunction cells (HJT/HIT) are traditional crystalline silicon cells and constitute the second generation of photovoltaic cell technology, while perovskite cells are representative of the third. generation of silicon-free thin film batteries.
Perovskite/crystalline silicon tandem cells are a combinationone of these two technical routes. They are double junction solar cells formed by superposition of perovskite solar cells and traditional crystalline silicon solar cells, in simple terms. refers to the connection of perovskite cells in series to the surface of crystalline silicon cells.
At present, pure perovskite cells have not yet completely overcome the problem of excessive efficiency degradation, and stacked cells based on perovskite and crystalline silicon are expected to become the best industrialized technology.
From the performance point of view, perovskite/crystalline silicon stacked cells expand the absorption spectrum due to the combination advantages and achieve higher photoelectric conversion efficiency than pure crystalline silicon cells or perovskite cells. Theoretically, the conversion efficiency can exceed 30%.
In terms of theoretical limit conversion efficiency, the limit efficiencies of HJT, TOPCon and perovskite monolayer cells are 27.5%, 28.7% and 31%, respectively.
It should be noted that stacked perovskite/crystalline silicon cells are expected to create more opportunities for heterojunction cells represented by HJT. This is because heterojunction battery technology and perovskite battery technology are low temperature processes. The production equipment of the two technologies is relatively compatible. Additionally, heterojunction batteries generate electricity from both sides and use thin-film processes.
Perovskite technology is therefore easier to stack on the basis of heterojunction cells. TOPcon battery technology is a high temperature process and does not have a transparent conductive film itself. It is naturally more difficult to suprpose perovskite technology as heterojunction technology.