The development of nanotube based solar cells has been accelerated. Single wall carbon nanotubes (SWNTs) have attracted great attention because of their unique chemical and physical properties. According to the research of gu1di in the Radiation Laboratory of Natre Dame University in the United States, the importance of single-walled carbon nanotubes is that they can develop and utilize the functionality and functionality of their electron donor assemblies. The research found that adding different atomic groups can make the nanotubes achieve the functional goal, which is expected to be used to produce a wide range of electronic components – solar cells.
Gu1di and his colleagues attached ferrocene to the wall of single-walled carbon nanotubes. This cyclization reaction involves the closure of the ring between the atoms in ferrocene molecules and the two carbon atoms of nanotubes. About one unit of ferrocene is attached to every 100 nanotubes. Ferrocene complex is an aggregation of iron atoms inserted between two five membered carbon rings, which can be used as electron donors. If these carbon nanotubes are irradiated with visible light, they can be used as donors of electrons released by ferrocene. Researchers have for the first time introduced the basis for developing fuel cells based on improved carbon nanotubes.
Researchers at Cornell University in the United States used carbon nanotubes to replace traditional silicon tubes to produce high-efficiency solar cells (Figure 1.11). The key to this technology is to use carbon nanotubes to replace traditional silicon tubes to produce photodiodes, which are the basic components of solar cells. Researchers used lasers of different colors to study this diode and found that it can double the current intensity in the process of converting light energy into electrical energy. Researchers pointed out that carbon nanotubes are an ideal photodiode because they can make full use of excess light energy, which is often lost in the form of heat in traditional solar cells. This research result was published in the online edition of Science in 2009. Nathan Gabor, the first author of the paper and a graduate student of Cornell University, said, “we not only found a new material, but also applied it to make real solar cells.” However, the researchers pointed out that they have only made high-efficiency solar cells in the laboratory at present, and further research is needed to mass produce a new generation of cheap and reliable solar cells.
Berkeley Laboratory and the University of California in the United States developed the preparation of inorganic nanocrystals from solution and used as ultra-thin solar cells for the first time. This nanocrystalline solar cell is cheap and easier to manufacture than solar cells made from organic polymers, because it does not contain organic materials and is more stable in the air. The rod-shaped nano-sized crystals of two semiconductors (selenium saw and cadmium chloride) were synthesized respectively, then dissolved in solution and cast on the conductive glass matrix. The efficiency of the obtained film to convert sunlight into electrical energy was 3%. Although this efficiency is lower than that of organic polymers (theoretically, the efficiency can reach 20% – 25%), this nanocrystalline solar cell is ultra-thin and processed by solution, which shows that it has the potential to reduce costs. Most solar cells are based on silicon and need to be assembled and controlled under conditions such as high vacuum and temperature of 400-1400 ℃.
Chemists at Buffalo University (UB) in the United States have developed a new method to thicken chemically pure zinc oxide films through dense nanostructures and develop a new method to deposit them on temperature sensitive substrates such as polymers and plastics (Figure 1.12). This research result has been published in the journal Physical Chemistry. By depositing general zinc oxide films on flexible surfaces, more efficient solar cells, liquid crystal displays, chemical sensors and optoelectronic facilities have been developed. Research shows that high-quality zinc oxide films can be made into many shapes, including films, nanorods and nanoparticles. However, the problem is that it is usually deposited at high temperature, which will harm or even melt the matrix. The technology developed by UB chemists enables metal oxide molecules to be safely cooled and coated on a temperature sensitive substrate.
Researchers at Illinois State University in the United States have found that placing silicon nanoparticle films on silicon solar cells can improve power output, reduce heat, and extend the life of solar cells. Research shows that combining the high-quality film of silicon nanoparticles with silicon solar cells can improve the power output function in the UV spectral range by 60%. Researchers at the Beckman Institute of Illinois State University also found that the power output function in the visible spectral range can be improved by 10% by using nanoparticles with a size of 2.85nm. In conventional solar cells, ultraviolet light is filtered or absorbed by silicon and converted into potentially harmful heat without generating electricity. However, in previous work, researchers have effectively coupled ultraviolet light with nanoparticles of appropriate size to generate electricity. In order to make improved solar cells, researchers began to use the patented process developed to convert large silicon into discrete, nanometer sized particles. Depending on their size, these nanoparticles will appear in a light wasting color. Nanoparticles of the required size are dispersed in isopropyl alcohol and then dispersed on the surface of solar cells. With the evaporation of alcohol, the nano particle film is left on the surface of the solar cell (Fig. 1.13). The research shows that the solar cell coated with 1nm film can increase the power output by about 60% for the spectrum in the ultraviolet range, but for the visible range, the power output is increased by less than 3%. The improved performance is to increase the voltage rather than the current. The process of coating solar cells with silicon nanoparticles can be easily combined in the manufacturing process, with only a small increase in cost.
Researchers at the Dutch Delft University of technology and the foundation for fundamental research in matter found that very small specific semiconductor crystals can produce an “avalanche effect” of electrons. This physical effect paves the way for the production of low-cost, high-power solar cells. This discovery may lead to new solar cells made of semiconductor nanocrystals (with crystal sizes in the nanometer range). In traditional solar cells, one photon can only release one electron accurately, while in some semiconductor nanocrystals, one photon can release two or three electrons, which is the so-called “avalanche effect”. These released free electrons can ensure the operation of solar cells and provide electricity. The more electrons released, the greater the output power of solar cells. This theoretically leads to the maximum output energy efficiency of solar cells correctly composed of semiconductor nanocrystals reaching 44%, and helps to reduce production costs.
Scientists at bar-i1an University in Israel announced in early 2008 that solar cells produced by nanotechnology can be 100 times larger than typical solar cells The nanotechnology Department of bar-i1an university completed this technology development. In the patented technology, researchers verified that the efficiency of the solar cell formed by embedding metal wires in conductive glass is similar to that of conventional silicon-based solar cells, but the production is much cheaper. Professor z a ban once produced a photovoltaic cell with a size of 1cm2, and now the size of the cell can reach 10cm × 10cm, which improves the use of this technology for commercial solar hair pond.
The University of California announced in mid May 2008 that it had developed a solar cell strengthened with nanowires in the laboratory, and is expected to launch high-efficiency thin-film solar cells in the future (Figure 1.14). The research results show that phosphide steel (INP) nanowires can be used as an electronic superhighway. This superhighway can spread loose and jumping electrons through light photons, making them directly enter the electrode in the facility to attract electrons. At the same time, this state will help to improve the conversion efficiency of thin-film solar cells. The new design can increase the number of electrons, which can enter the electrode through the light absorbing polymer. By reducing electron hole recombination, engineers at the University of California, San Diego, have verified ways to improve efficiency. In this way, sunlight can be converted into electricity in thin-film photovoltaic.
Unidym, a subsidiary of arrowhead research in the United States, and Kayaku in Japan formed a joint venture to combine unidym’s printed transparent electrodes into Kayaku’s thin-film solar cells. Thin film solar cells need transparent electrode materials in order to optimize photoelectric conversion efficiency. Unidym’s carbon nanotube based electrodes provide excellent results for the thin film solar cell materials currently used by Kayaku company, such as steel tin oxide (ITO). Unidym’s carbon nanotube based electrode brings several advantages to Ito’s manufacturing of solar cells, including good compatibility with high-yield roll manufacturing technology, low material cost and improved production flexibility. This printed electrode based on carbon nanotubes can greatly improve the production economy of some innovative solar companies such as Kayaku, and can be widely used in solar power generation.
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