First, a basic introduction to GaAs cells
In recent years, solar photovoltaic power generation in the global progress has been made. PV cells are generally used polysilicon and monocrystalline silicon cells, however, the
laptop battery supply of polysilicon due to the limited capacity of raw materials, coupled with the speculation of international speculators, leading to the international market price of polysilicon soaring, the past year, due to the impact of the economic crisis, prices fell, but the status of shocks to the healthy development of photovoltaic industry difficult. At present, the technical solution to this difficulty there are two ways: First, thin-film solar cells, concentrator solar cell 2 is used, reduce the quantity of raw material dependence. Conversion rate of less commonly used thin-film batteries, so a new type of high-powered condenser
Inspiron E1505 battery systems by researchers attention [1]. Concentrator solar cell is to use convex lens or a parabolic mirror to focus sunlight into several times, several times or several hundred times or even thousands of times, and then projected onto the solar cells. Then the corresponding solar cell may have a multiple of electric power. They have a high conversion rate, the
XPS M1210 battery supplies an area of small and less benefits. High-power condenser battery is a typical gallium arsenide (GaAs) solar cells.
GaAs belongs to III-V compound semiconductor materials, its energy gap with the more suitable for matching the solar spectrum, and can heat. Compared with silicon solar cells, GaAs solar cell has a good performance [2].
Second, GaAs cells and comparison of silicon photovoltaic cells [3]
1, photoelectric conversion rate:
GaAs band gap than silicon-wide, making it the spectral response and spatial ability to match the solar spectrum better than the silicon. At present, the theoretical efficiency of silicon cells approximately 23%, while the theory of single-junction GaAs cell efficiency of 27%, while the theory of multi-junction GaAs cell efficiency of more than 50%.
2, temperature resistance
Routine, the gallium arsenide cell temperature resistance is better than the silicon solar cells, there are experimental data indicate that GaAs cells under the conditions at 250 ℃ can still work, but the silicon photovoltaic cells at 200 ℃ had been unable to function properly.
3, mechanical strength and the proportion of
Than in the physical properties of gallium arsenide on silicon to be more brittle, which is making it easier to fracture than the processing time, so its now often made of thin films, and use the substrate (often for Ge [Ge]),
Inspiron 9300 battery to resist disadvantage in this regard, but it also increases the technical complexity.
Third, the technological development of the battery status of GaAs
1, History
GaAs solar cell development is 50 years from the beginning of the last century, has been more than 50 years of history. First discovered in 1954, the world’s GaAs material has a photovoltaic effect. In 1956, Loferski JJ and his team of the best materials to manufacture solar cells of the physical properties, they pointed out that the Eg in the 1.2 ~ 1.6 eV within the scope of material has the highest conversion efficiency. (GaAs materials, Eg = 1.43 eV, within the framework of the above-mentioned high-efficiency, in theory, estimate, GaAs single-junction solar cell efficiency of up to 27%). The 20th century, 60s, Gobat and other developed first a zinc-doped GaAs solar cell, but the conversion rate is not high, only 9% ~ 10%, well below the 27% of the theoretical value. The 20th century, 70 years, IBM Corporation and the former Soviet Union Ioffe Technical Physics, as represented by the research unit, using LPE (Liquid Phase Epitaxy) technology into the GaAlAs heterojunction window layer, reducing the GaAs surface recombination velocity, so that the efficiency of GaAs solar cells up to 16%. Soon, the United States, HRL (Hughes Research Lab) and the Spectro lab through improvements in the LPE technology makes the battery, the average efficiency of 18%, and achieved mass production, created a high-efficiency GaAs solar cells a new era [4]. From the last century, after 80 years, GaAs solar cell technology has gone from LPE to MOCVD, from homogeneous to heterogeneous epitaxial extension, from a single node to multi-junction stacked structure of several stages of development, the development of the rapid pace of efficiency continuously improve the current laboratory has reached 50% maximum efficiency (from the IBM corporate data), industrial production conversion rate of up to 30%.
2, several basic technical introduction
GaAs mode of production is different from the traditional mode of production silicon wafers, GaAs production requires use of epitaxial techniques, such epi-wafer is usually 4-6 inches in diameter, compared with 12-inch silicon wafer is much smaller, therefore, Preparation of the epi-wafer require special machine. At present, the technology commonly used in the preparation of GaAs there are several, mainly such as LPE and MOVPE.
2.1 LPE Technology
Liquid phase epitaxy (Liquid Phase Epitaxy, referred to as LPE) 1963 proposed by Nelson and others, in the production of GaAs, its to low melting point of Ga) Ga) as the solvent, to be grown materials Ga, As (arsenic), and dopant Zn (zinc), Te (tellurium), Sn (tin), etc. for the solute, so that solute in a solvent saturated or too saturated. Cooled by cooling so that the graphite boat of the solute from the solvent precipitation, in the directional growth of a layer of single-crystal substrate crystal structure and lattice constant of single-crystal substrates (often as Ga) sufficiently similar GaAs crystalline material, the crystal structure of continuity, to achieve the epitaxial growth of crystals.
2.2 MOVPE Technology
Metal organic chemical vapor deposition (MOCVD) by the United States such as Rockwell’s HM Manasevit first proposed in 1968 as a preparation of single crystal compound semiconductor thin-film vapor-phase epitaxial growth of new technology. In the preparation of GaAs chip, which uses organic compounds Ga and As elements of hydride crystal growth, etc., as raw material, thermal decomposition method on the substrate vapor phase epitaxy, the growth of GaAs compound semiconductors and their solid solutions in thin-film multi – layer of single crystal materials. MOCVD is the pressure or low pressure (≈ 10kPa) pass under the H2 of the cold wall quartz reactor carried out, the substrate temperature of 600-800 ℃, the process need to use radio-frequency heating of graphite frame, so that H2 gas through a temperature-controlled bring the liquid metal organic source of bubbling to the growing areas. Present MOVPE prepared by the growth rate of GaAs thin-film batteries, growth temperature and As / Ga ratio, the purity of metal organic
HD438 battery and AsH3 and many other parameters [5].
3, the development of domestic technology
In the last century, the mid-70s to the mid-90s, the domestic L PE commonly used technology research and GaAs cells, single-junction GaAs / GaAs cell efficiency up to 20%. Since 1995, China began to use MOCVD technology research and GaAs cells. “15″ initially, single-junction GaAs / Ge cell mass production (for space), the average production efficiency of 18. 5% ~ 19. 0% (AM0). China’s first GaAs cell test was conducted in September 1988, when, and with the launch of the FY21A star on the square in the satellite’s solar panels used on the 20mm × 20mm × 0.3mm single-junction GaAs cell, to achieve better results . In January 2001 launch of “Shenzhou-3″ spacecraft and in May 2002 launch of the “Ocean 21″ satellite, also applied the single-junction GaAs / GaAs cells [6].
Fourth, the development of GaAs battery industry status quo
On the world’s point of view, GaAs cells are mainly used in space exploration and utilization aspects, on the ground using less. At present the world production of gallium arsenide concentrator cells specialized factories are the United States Emcore, SpectroLab (a subsidiary of Boeing) and Germany’s Azur Space, etc. to promote the industrialization of China has not yet formed.
In August 2007 onward, due to condensing technology adoption, gallium arsenide, the use of the battery from the satellites into the scale concentrating solar power plant applications. To this end, Emcore company spent 10 million U.S. dollars, will increase in production capacity to the current 150 megawatts per year.
In 2008, global production of gallium arsenide cell breakthrough development in April, as the production of gallium arsenide, one of the world’s leading manufacturers Spectro Lab, access to 350 MW, 93 million U.S. dollars (1000 times the condenser) of power station orders.
In East Asia, but also the production of an initial promotion, in May 2008, South Korea received a 70-megawatt power plant on, 28 million U.S. dollars (500 times the condenser) orders.
With the global PV industry, large-scale development, the production
dell Inspiron 1721 battery,
dell Inspiron 1520 battery of photovoltaic cells and gradually expand.
5, gallium arsenide, the problems encountered by the battery industry
GaAs photovoltaic cells with conversion efficiency on better, there are clear advantages for development, should be an effective means of photovoltaic power generation, but the current aspects of industrialization in China is not ideal, there have been some problems and obstacles. Mainly in the following aspects, first, preparation of the cost remains high, it has been reported in the literature, preparation of gallium arsenide chips cost about 10000 $ / m2, than conventional silicon cells compared to much higher, of course, this is a few aspects of factors, on the one hand, due to Ga elements in the global reserves of small, probably around 2 million tons [7] (about half of China), and mining is difficult (usually associated bauxite mine), In today’s call to reduce high energy-consuming investment in the request (electrolytic aluminum projects are strictly controlled), the short term to expand the production of thick gallium more difficult. On the other hand, due to the purity requirements of semiconductor materials, high demand for semiconductors using gallium-up 6-7 months 9, currently the world’s master purification techniques such countries only the United States, Germany and Japan a few, due to technical monopoly, constitutes a restriction on the expansion of reproduction, an overall increase preparation costs. Second, another component of gallium arsenide, arsenic toxic, environmental safety and production workers for their own physical safety is a no small threat, in the absence of a strong technical assurance under the premise of the enterprise in general do not want to put into this talent . Thirdly, the current GaAs cells due to their own physical constraints (brittle), generally made of thin-film batteries with the substrate needs to construct the tunnel junction and prevent the formation of parasitic p / n junction [8], which increases the technical more difficult. Fourth, due to the high conversion rate of gallium arsenide cells, often made of high its condenser batteries
F4486B battery,
F4809A battery,
F4812A battery, of course, that could reduce the supplies, for reducing costs and benefits, but there are also need to chase on the issue tracking system, and because of the sunshine conditions are not the same as the region learned that the current DAY tracking system requirements are not the same, but also increase system complexity and implementation difficulties [9]. Fifth, the domestic market in recent years attention has focused on the polysilicon market, and is carried out in a more than 90% dependence on imported raw materials more than 90% of export products rely on a model, did not focus on Localization of PV promotion, the long run, the entire PV industry will have no power demand, which is the development of gallium arsenide cell industry is also unfavorable. Sixth, for the industrialization, the public recognition is very important, all these years, for gallium arsenide photovoltaic cells, the public recognition is not enough, the media and research institutions, some poor publicity and promotional activities. 7th is national policy, government policy support in the photovoltaic industry in more macro, is still not done right sub-categories of photovoltaic cells to treat industries and support industrial development, cost-competitive advantages does not have the circumstances, the policy support of the weak so that the slow progress in the industrialization of gallium arsenide. Synthesis of these reasons appear to the development of gallium arsenide cell industry poses an obstacle.
5, Countermeasures
View of the current problem, I think we can proceed to the following aspects to efforts to resolve. First of all, you need to do kung fu on the gallium raw material, although the gallium is not too much global reserves, but China is relatively rich, the current purification techniques, but the problem is off the issue, which requires the large number of the relevant scientific research institutions research, do a good job of high-purity gallium extraction. The second is to do a good job safety and security measures to enhance the intelligent factory automation, to reduce direct contact with production staff, ensuring security and safety of production and reduce environmental resistance. The third is to increase technology research, simplified preparation process, reducing the battery system complexity and reduce the battery prepared to spend. Fourth, the media and relevant academic institutions to step up propaganda work of recommending to raise public awareness. 5th is national policy to support the details of, for example on the photovoltaic power generation for the battery industry, for crystalline silicon cells, thin film batteries, gallium arsenide cells, batteries, etc. chromium telluride the industrialization of the production
Business Notebook nc6120 battery and classification treatment, foster competition in some GaAs power battery production enterprises, while encouraging the use of photovoltaic power plants around the new gallium arsenide photovoltaic cells.
6, Prospect
At present due to financial, technological and social aspects of cognitive deficiencies, gallium arsenide cells in China, did not enter public life, to achieve industrial production. However, due to GaAs cells with high energy conversion efficiency, personal opinion, is a relatively promising photovoltaic devices, to promote new energy future human use, and create a good living environment clean and prepare options, I believe that through the joint efforts of industry, government policies on the effective support of the public open heart treatment, gallium arsenide solar cells industrialization will gradually develop steadily in the extensive use of tomorrow’s not a dream!