The difference between polycrystalline silicon and monocrystalline silicon is mainly reflected in physical properties. For example, the anisotropy of mechanical, optical and thermal properties is much less obvious than that of single crystal silicon in terms of electrical properties, the conductivity of polycrystalline silicon crystal is also much less than that of single crystal silicon, and does not have even almost no conductivity. In terms of chemical activity, the difference between the two is very small and polysilicon is generally used more often.
Monocrystalline silicon cells have high cell conversion efficiency and good stability, but their cost is high. More than 20 years ago, monocrystalline silicon cells broke the technical barrier of photoelectric conversion efficiency of more than 20%. The cost of polycrista silicon cellsllin is low and the conversion efficiency is slightly lower than that of Czochralski monocrystalline silicon solar cells. Various defects in the material, such as grain boundaries, dislocations, micro defects, carbon and oxygen impurities in the material, and contamination during the process. Transition metals are believed to be responsible for the inability of polycrystalline silicon cells to exceed the 20% photoelectric conversion rate. Researchers at Germany's Fraunhofer Institute adopted new technologies and were the first in the world to achieve a photoelectric conversion rate of polycrystalline silicon solar cells of 20.3%.
How to make your own solar cells
Some answers from Baidu Solar chips should refer to solar panels 1 Silicon-based solar cells 1.1 Monocrystalline silicon solar cells TO silicon basesolar cells Among them, large 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. Nowadays, the electrical mass technology of single crystal silicon is almost mature. In battery production, surface texturing, emitter zone passivation, zoned doping and other technologies are generally used. The developed batteries mainly include monocrystalline silicon planar cells and grooved gate electrode monocrystalline cells. silicon cell. 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 Institute for 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 improved electroplating process: the conversion efficiency of the battery produced above exceeds 23%, and the maximum value can reach 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 (2 cm) co efficiencynversion of Grooved Buried Gate Electrode Crystalline Silicon Cell (5cm) Monocrystalline silicon solar cells undoubtedly have the highest conversion efficiency and still dominate large-scale applications and industrial production. However, due to from the price of monocrystalline silicon materials and the corresponding tedious battery processes, the cost and price of monocrystalline silicon remains high less, if you want to make a big differenceIt is very difficult to reduce its cost In order to save materials. high quality and to find alternatives to monocrystalline silicon solar cells, thin film solar cells have been developed, of which polycrystalline silicon thin film solar cells and amorphous silicon thin film solar cells are typical representatives 1.2. Polycrystalline Silicon Thin Film Solar Cells CellsCrystalline silicon solar panels are typically fabricated on high-quality silicon wafers with a thickness of 350 to 450 μm. These silicon wafers are 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. Currently, polycrystalline silicon thin film batteries are mainly produced using chemical vapor deposition methods, including low pressure chemical vapor deposition (LPCVD) and enhanced chemical vapor deposition processes.by plasma (PECVD). Additionally, liquid phase epitaxy (LPPE) and sputter deposition methods can also be used to prepare polycrystalline silicon thin film batteries. Chemical vapor deposition mainly uses SiH2Cl2, SiHCl3, Sicl4 or SiH4 as reaction gas and reacts in a certain protective atmosphere to generate silicon atoms and deposit them on a heated substrate. Substrate materials generally use Si, SiO2, Si3N4, etc. However, studies have shown that it is difficult to form larger grains on substrates other than silicon, 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 indepositing thick polysilicon films. , therefore, recrystallization technology is undoubtedly a very important link. The currently used technologies mainly include solid phase crystallization method and intermediate zone 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 temperature 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 cheap substrate materials, theircost is much lower than that of monocrystalline silicon cells and their efficiency is higher than that. of amorphous silicon thin film cells, therefore, polycrystalline silicon thin film cells will soon dominate the solar energy market. 1.3 Amorphous silicon thin film solar cells 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 developed rapidly in 2008. Currently, many companies in the world producethis 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 itself insensitive to the long wavelength region of the radiation spectrum solar. This limits the use of amorphous silicon solar cells. . 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 conversion efficiency and solve the instability of single junction cells ares: ① It combines materials with different bandgap widths to increase the spectral response range ② Layer i of the upper cell is thinner, layer i of the upper cell is thinner. the electric field intensity generated by illumination does not change much, ensuring that the photogenerated carriers in layer i are extracted; ③ The carriers generated by the bottom cell are about half of those of the single cell, and the photofading effect is reduced; Each element of the stacked solar cell batteries is connected in series. There are many methods to prepare amorphous silicon thin film solar cells, including reactive sputtering, PECVD, LPCVD, etc. The gas reaction raw material is SiH4 diluted with H2, and the substrate is mainly glass and stainless steel sheets. Thin films can be transformed into cellssingle junction and tandem solar cells through different battery processes. At present, the research on amorphous silicon solar cells has achieved two major progress: firstly, the conversion efficiency of three-layer structure amorphous silicon solar cells has reached 13%, setting a new record; secondly, the annual production capacity of three-layer solar cells; solar cells have 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%. %. See Table 1. Highest mentioned above. the conversion efficiency is in a small area (0．25 cm2) obtained from the battery. It has been reported in the literature that the conversion efficiency of cellssingle junction amorphous silicon solar panels exceeds 12.5%. Japan's Academia Sinica adopted a series of new measures, and the conversion efficiency of the produced amorphous silicon solar cells was 13.2%. There is not much domestic research on amorphous silicon thin film cells, especially Geng Xinhua laminated solar cells of Nankai University and others used industrial materials and aluminum back electrodes to prepare one - 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 we can further solve the stability problem, large amorphous silicon solar cells are therefore sundoubtedly one of the main products in solar cell development.
What is the difference between monocrystalline silicon and polycrystalline silicon?
Tools/Materials:
Several small pieces of glass
Solar cells, EVA, photovoltaic backsheet, solder tapes and some tapes
p> < p>An electric soldering iron, a cell cutting machine and laminating equipment
A ruler, a wallpaper cutter, scissors and PVB gloves
>Make solar cells
< p>Method/steps:1. Firstly, design the size of the battery part according to the size of the glass. Generally, the distance between each side of the cell piece is 5mm from the edge of the stack. Glass With the main grid line of the battery as the center, use a cutting machine to cut the size of the battery piece. Cut the solar cells into several pieceswaters, the number is the same as the number of glass. operation and set aside for use after cutting.
2. Next, use a ruler and wallpaper knife to cut the EVA and backboard into several small pieces slightly larger than the glass. The amount of EVA should be twice that of glass. Gloves cut and ready to use.
3. Next, use scissors to cut the welding tape into several small sections slightly longer than the length of the glass. Wear PVB gloves when using. cutting use.
4. After completing the above material preparations, start using a soldering iron to solder the ribbons to the main grid lines on both sides of the battery part. Do not use too much force to avoid crushing the battery part.
5. Place the materials from bottom to top in the order glass-EVA-battery-EVA-backplate. Onceall are laid, place them in the laminator to avoid misalignment. can be fixed with adhesive tape.
6. Remove the small laminated solar panels. Once the temperature has returned to room temperature, use a wallpaper knife to remove excess material from around the glass. Finally, use a soldering iron to connect the small independent solar panels. in series, can be used.
Notes:
1. When handling raw materials, purification work should be carried out to avoid contamination of the raw materials.
2. When cutting battery sheets, the battery should be used to its fullest extent to avoid waste.
3. When soldering, avoid the temperature being too high to avoid damaging the battery performance.
1. The anisotropy of mechanical, optical and thermal properties is much less obvious than that ofu monocrystalline silicon
2. silicon crystal The electrical conductivity is also much less than that of single crystal silicon, and even has almost no electrical conductivity.
3. In terms of chemical activity, the difference between the two is very small, and polycrystalline silicon is generally used.
Detailed informationPolycrystalline silicon is a form of simple silicon. When molten elemental silicon solidifies under supercooled conditions, the silicon atoms are arranged in the shape of a diamond lattice to form numerous crystal nuclei. If these crystal nuclei transform into crystal grains with different crystal plane orientations, these crystal grains combine to form polycrystalline silicon. .
Use value: From the current development process of international solar cells, it can be seen that the development trendst are monocrystalline silicon, polycrystalline silicon, strip silicon, and thin film materials (including microcrystalline silicon-based films, compound-based films, and dye films).
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