Solar energy generally refers to the radiant energy of sunlight, which is generally used for power generation in modern times. Since the formation of the earth, living things have mainly relied on the heat and light provided by the sun. Since ancient times, humans have also learned to use sunlight to dry things as a way to preserve food, such as making salt and drying salted fish. However, with the decrease of fossil fuels, solar energy is deliberately further developed. There are two ways to utilize solar energy: passive utilization (photothermal conversion) and photoelectric conversion. Solar power generation is a new renewable energy. In a broad sense, solar energy is the source of a lot of energy on the earth, such as wind energy, chemical energy, potential energy of water and so on.
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history
The word "photovoltaic" comes from Greek, which means light, volt and electricity. It comes from the name of Italian physicist Alessandro Volta. After Alessandro Volta, "Volt" was used as the unit of voltage.
Solar cells (18)
In the history of solar energy development, as early as19th century, it was found that light irradiation caused "lighting electricity" on materials.
1839, the photovoltaic effect was first discovered by French physicist A.E.Becquerel, and the word "photovoltaic" only appeared in English in 1849.
1883 Charles fritter successfully prepared the first solar cell. Charles formed a semiconductor metal junction by covering a germanium semiconductor with an extremely thin gold layer, and the efficiency of the device was only 1%.
In the 1930 s, the principle of photovoltaic power generation was widely used in the exposure meter of cameras.
1946 Russell Ohl applied for a patent for manufacturing modern solar cells.
1950s, with the gradual understanding of the physical properties of semiconductors and the progress of processing technology, the first solar cell was born in Bell Laboratories when bell laboratory discovered that silicon doped with a certain amount of impurities was more sensitive to light. The era of solar cell technology has finally arrived.
Since the1960s, all satellites launched by the United States have used solar cells as energy sources.
During the energy crisis of1970s, countries all over the world realized the importance of energy development.
1973 oil crisis, people began to turn the application of solar cells to general people's livelihood.
At present, in the United States, Japan, Israel and other countries, a large number of solar devices have been used and are moving towards the goal of commercialization.
Among these countries, the United States established the world's largest solar power plant in California in 1983, with a power generation capacity as high as160,000 watts. South African countries such as South Africa, Botswana and Namibia have also set up projects to encourage the installation of low-cost solar cell power generation systems in remote rural areas.
Japan is the most active country in promoting solar power generation. 1994, Japan implemented the subsidy and reward law to promote the "grid-connected parallel solar photovoltaic system" with 3000 watts per household. In the first year, the government subsidized 49% of the funds, and then the subsidies decreased year by year. "Grid-connected parallel solar photovoltaic energy system" means that solar cells provide power for their own loads under the condition of sufficient sunshine, and if there is excess power, it is stored separately. When there is insufficient or no power generation, the required power will be provided by the power company. By 1996, 2600 households in Japan have installed solar power generation systems with a total installed capacity of 8 million watts. A year later, 9,400 were installed, with a total installed capacity of 32 million watts. In recent years, due to the rising awareness of environmental protection and the government subsidy system, it is estimated that the demand for solar cells in Japan will also increase rapidly.
In China, the solar power generation industry is also strongly encouraged and subsidized by the government. In March 2009, the Ministry of Finance announced plans to subsidize large-scale solar energy projects such as solar photovoltaic buildings.
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The principle of solar cells
Sunlight shines on the semiconductor pn junction, forming a new hole-electron pair. Under the action of pn junction electric field, holes flow from P region to N region, and electrons flow from N region to P region. When the circuit is connected, a current is formed. This is the working principle of photoelectric effect solar cells. Solar Green Energy There are two ways of solar power generation, one is light-heat-electricity conversion, and the other is light-electricity direct conversion.
Optical-thermal-electrical conversion
(1) The optical-thermal-electrical conversion mode uses the thermal energy generated by solar radiation to generate electricity. Generally, the absorbed heat energy is converted into working medium steam by solar collectors, and then the steam turbine is driven to generate electricity. The former process is photothermal conversion process; The latter process is a thermoelectric conversion process, just like ordinary thermal power generation. The disadvantages of solar thermal power generation are low efficiency and high cost. It is estimated that its investment is at least 5 ~ 10 times more expensive than that of ordinary thermal power plants. A solar thermal power plant with a capacity of 1000MW needs to invest 2-25 billion USD, and the average investment of 1kW is 2,000-25,000 USD. Therefore, at present, it can only be used in small-scale special occasions, and large-scale utilization is not economical and cannot compete with ordinary thermal power plants or nuclear power plants.
Direct photoelectric conversion
(2) photoelectric direct conversion mode This mode directly converts solar radiation energy into electric energy by photoelectric effect, and the basic device of photoelectric conversion is solar cell. Solar cell is a device that directly converts solar energy into electric energy due to photovoltaic effect, and it is a semiconductor photodiode. When the sun shines on the photodiode, the photodiode will convert solar energy into electric energy and generate current. When a plurality of batteries are connected in series or in parallel, it can become a solar cell array with relatively high output power. Solar cell is a promising new power supply, which has three advantages: permanence, cleanness and flexibility. Solar cells have a long life, and as long as the sun exists, they can be used for a long time at a time. Compared with thermal power generation and nuclear power generation, solar cells will not cause environmental pollution; Solar cells are large, medium and small, ranging from medium-sized power stations with a million kilowatts to solar cells that can only be used by one family, which are unmatched by other power sources.
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Present situation of solar cell industry
At present, thin-film solar cells working with photoelectric effect are the mainstream, while wet-type solar cells working with photochemical effect are still in the embryonic stage.
Present situation of battery industry in global solar
According to the statistics of Dataquest, at present, there are 136 countries in the world, among which 95 countries are developing solar cells on a large scale and actively producing various related energy-saving new products. 1998 The total power generation of solar cells produced in the world reached 100 MW, and 1999 reached 2850 MW. According to the forecast of European Photovoltaic Industry Association EPIA in 2008, if the global installed capacity is 2.4GW in 2007, the global annual installed capacity will reach 6.9 GW, 56GW and 28 1GW in 2020 and 2030 respectively, and the global cumulative installed capacity in 20 10 will be 25.4GW. Global solar's battery production is growing at a compound annual growth rate of 47%, reaching 6.9 GW in 2008.
At present, many countries are making medium and long-term solar energy development plans, preparing to develop solar energy on a large scale in 2 1 century. The U.S. Department of Energy launched the National Photovoltaic Program, and Japan launched the Sunshine Program. The NREL photovoltaic plan is an important part of the national photovoltaic plan of the United States. The plan carries out research work in five areas: monocrystalline silicon and advanced devices, thin film photovoltaic technology, PVMaT, photovoltaic modules and system performance, solar cell vehicles and engineering, photovoltaic application and market development.
The United States has also launched the "Solar Street Lamp Program", aiming at changing street lamps in some cities in the United States to solar power supply. According to the plan, each street lamp can save electricity by 800 degrees per year. Japan is also implementing "70,000 solar energy projects". The solar residential power generation system to be popularized in Japan is mainly solar cell power generation equipment installed on the roof of the house, and the surplus electricity used by households can also be sold to power companies. A standard home can install a system that generates 3000 watts. In Europe, the research and development of solar cells was included in the famous "Eureka" high-tech plan, and "654.38+10,000 sets of engineering plan" was launched. These "solar projects" with the popularization and application of photovoltaic cells as the main content are one of the important driving forces to promote the great development of solar photovoltaic cell industry at present.
Japan, South Korea and eight European countries recently decided to cooperate to build the world's largest solar power station in inland Asia and desert areas in Africa. Their goal is to effectively use the long-term sunshine resources in desert areas, which account for about 1 4 of the global land area, and provide110,000 kilowatts of electricity for 300,000 users. The plan will start from 200 1 and take 4 years to complete.
At present, the United States and Japan have the largest share of photovoltaic market in the world. The United States has the world's largest photovoltaic power station with a power of 7MW, and Japan has also built a photovoltaic power station with a power of 1mw. There are 230,000 photovoltaic devices in the world, with Israel, Australia and New Zealand leading the way.
Since 1990s, the battery industry in global solar has been developing continuously with an annual growth rate of 15%. According to the latest statistics and forecast report released by Dataquest, from 65438 to 0998, the total investment of the United States, Japan and western European industrialized countries in solar energy research and development reached 57 billion dollars. 1999 was $654.38+64.6 billion; $70 billion in 2000; 200 1 year will reach $82 billion; It is estimated that it will exceed $6,543.8 trillion in 2002.
Present situation of solar cell industry in China
China attaches great importance to the research and development of solar cells. As early as the Seventh Five-Year Plan period, the research of amorphous silicon semiconductor was included in the national major topic. During the Eighth Five-Year Plan and the Ninth Five-Year Plan, the research and development of China focused on large-area solar cells. On June 5438+00, 2003, the National Development and Reform Commission and the Ministry of Science and Technology formulated the development plan of solar energy resources in the next five years. The "Bright Project" of the National Development and Reform Commission will raise 10 billion yuan to promote the application of solar power generation technology, and it is planned that the total installed capacity of solar power generation systems in China will reach 300 MW by 20 15. China has become the largest producer of photovoltaic products in the world. In the upcoming new energy revitalization plan, the installed capacity of photovoltaic power generation in China is planned to reach 20GW in 2020, which is more than 1.8GW of the original 10 times of the medium and long-term plan for renewable energy.
In 2002, the relevant ministries and commissions of the state launched the "Power-on Plan for Rural Areas without Electricity in the West", which solved the power consumption problem of polysilicon solar cells in rural areas without electricity in seven western provinces through solar energy and small-scale wind power generation. The start of this project has greatly stimulated the solar power generation industry, and a number of solar cell packaging lines have been built in China, which has rapidly increased the annual output of solar cells. According to experts' prediction, the current photovoltaic market demand in China is 5 MW per year. From 200 1 to 20 10, the annual demand will reach 100 MW. Starting from 20 1 1, the annual demand of photovoltaic market in China will be greater than 20MW.
At present, domestic solar monocrystalline silicon producers mainly include Luoyang monocrystalline silicon factory, Hebei Ningjin monocrystalline silicon base and Sichuan Emei semiconductor material factory, among which Hebei Ningjin monocrystalline silicon base is the largest solar monocrystalline silicon production base in the world, accounting for about 25% of the world solar monocrystalline silicon market share.
In the downstream market of solar cell materials, at present, domestic companies producing solar cells mainly include Hongwei Group, Wuxi Suntech, Hairun Photovoltaic, Nanjing Zhongdian, Baoding Yingli, Hebei Jingao, Jieni New Energy, Suzhou Artes, Changzhou Tianhe, Tuori New Energy, Yunnan Tianda Photovoltaic Technology, Ningbo Solar, Kyocera (Tianjin) Solar and other companies, with an annual total production capacity of over 800MW.
In 2009, according to the report provided by Gong Xin, the State Council pointed out that polysilicon was overcapacity, but the actual industry did not recognize it. The Ministry of Science and Technology has said that there is no overcapacity in polysilicon [1].
Analysis of solar cells and the prospect of solar power generation
At present, the application of solar cells has entered the fields of industry, commerce, agriculture, communication, household appliances and public facilities from the military and aerospace fields, especially in remote areas, mountainous areas, deserts, islands and rural areas, in order to save expensive transmission lines. However, at present, its cost is still very high, and tens of thousands of dollars are needed to generate 1kW power, so its large-scale use is still limited economically.
However, in the long run, with the improvement of solar cell manufacturing technology and the invention of new photoelectric conversion devices, environmental protection and the huge demand for renewable and clean energy in various countries, solar cells will still be a feasible method to utilize solar radiation energy, which will open up broad prospects for human beings to use solar energy on a large scale in the future.
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Classification of solar cells
Brief introduction of solar cell classification
According to the crystalline state, solar cells can be divided into two categories: crystalline thin film type and amorphous thin film type (hereinafter referred to as a-), while the former is divided into single crystal type and polymorphic type.
According to materials, it can be divided into silicon thin films, compound semiconductor thin films and organic thin films, and compound semiconductor thin films can be divided into amorphous (a-Si:H, a-Si:H:F, a-SixGel-x:H, etc. ), III V group (GaAs, InP, etc. ), group II VI (Cds system) and zinc phosphide (Zn 3 p 2).
According to the different materials used, solar cells can also be divided into: silicon solar cells, multicomponent compound thin film solar cells, polymer multilayer modified electrode solar cells, nanocrystalline solar cells, and organic solar cells, among which silicon solar cells are the most mature and dominant in application.
(1) silicon solar cell
Silicon solar cells are divided into monocrystalline silicon solar cells, polycrystalline silicon thin-film solar cells and amorphous silicon thin-film solar cells.
Monocrystalline silicon solar cells have the highest conversion efficiency and the most mature technology. The highest conversion efficiency in the laboratory is 24.7%, and the highest mass production is 15%. It is still dominant in large-scale application and industrial production, but the cost of monocrystalline silicon is high, so it is difficult to significantly reduce the cost. In order to save silicon materials, polycrystalline silicon thin films and amorphous silicon thin films have been developed as alternative products of monocrystalline silicon solar cells.
Compared with monocrystalline silicon, polycrystalline silicon thin-film solar cells have lower cost and higher efficiency than amorphous silicon thin-film solar cells. The highest conversion efficiency in laboratory is 18%, and the conversion efficiency in industrial scale production is 10%. Therefore, polycrystalline silicon thin film batteries will soon dominate the solar panels of the International Space Station in the solar power market.
Amorphous silicon thin-film solar cells have the advantages of low cost, light weight, high conversion efficiency, convenience for mass production and great potential. However, due to the decrease of photoelectric efficiency caused by its materials, its stability is not high, which directly affects its practical application. If we can further solve the stability problem and improve the conversion rate, then amorphous silicon solar cells will undoubtedly be one of the main development products of solar cells.
(2) Multi-compound thin film solar cells
Multi-compound thin film solar cells are inorganic salts, mainly including gallium arsenide III-V compounds, cadmium sulfide, cadmium sulfide and copper indium selenium thin film cells.
Polycrystalline thin-film batteries of cadmium sulfide and cadmium telluride have higher efficiency than amorphous silicon thin-film solar cells, lower cost than monocrystalline silicon batteries, and are easy for mass production. However, because cadmium is highly toxic, it will cause serious pollution to the environment, so it is not the best substitute for crystalline silicon solar cells.
The conversion efficiency of gallium arsenide (GaAs) III-V compound battery can reach 28%. GaAs compound material has ideal optical band gap, high absorption efficiency, strong radiation resistance and is insensitive to heat, which is suitable for manufacturing high-efficiency single-junction batteries. However, the high price of GaAs material greatly limits the popularity of GaAs batteries.
Copper-indium-selenium thin film battery (CIS) is suitable for photoelectric conversion, and there is no photo-degradation problem, and the conversion efficiency is the same as that of polysilicon. It has the advantages of low price, good performance and simple process, and will become an important direction of solar cell development in the future. The only problem is the source of the materials. Because indium and selenium are relatively rare elements, the development of such batteries is bound to be limited.
(3) polymer multilayer modified electrode type solar cell
Replacing inorganic materials with organic polymers is a new research direction of solar cell manufacturing. Organic materials are of great significance to the large-scale utilization of solar energy and the provision of cheap electricity because of their good flexibility, easy manufacture, wide sources of materials and low cost. However, the research on the preparation of solar cells from organic materials has just begun, and it can not be compared with inorganic materials, especially silicon cells, in terms of service life and battery efficiency. Whether it can be developed into a product with practical significance needs further research and exploration.
(4) Nanocrystalline solar cells
Nano-titanium dioxide crystal chemical energy solar cell is newly developed, which has the advantages of low cost, simple process and stable performance. Its photoelectric efficiency is stable above 10%, its manufacturing cost is only1/5 ~1/and its service life can reach more than 20 years.
The research and development of this battery has just started, and it will gradually enter the market in the near future.
(5) Organic solar cells
Organic solar cells are solar cells with organic materials as the core. Everyone is not familiar with organic solar cells, which makes sense. Today, more than 95% of mass-produced solar cells are silicon-based, and the remaining less than 5% are made of other inorganic materials.
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Production technology of solar cells (modules)
package
Assembly line is also called packaging line, and packaging is a key step in solar cell production. Without a good packaging process, no matter how good the battery is, it will not produce a good assembly board. The packaging of the battery can not only ensure the battery life, but also enhance the battery resistance. High quality and long service life of products are the key to win customer satisfaction, so the packaging quality of component boards is very important.
Process:
1, battery inspection -2, front welding-inspection -3, back series-inspection -4, laying (glass cleaning, cutting, glass pretreatment, laying) -5, laminating -6, deburring (trimming and cleaning) -7, framing (gluing, corner pieces, etc.).
How to ensure the high efficiency and long life of components;
1, high conversion efficiency, high quality battery;
2. High-quality raw materials, such as EVA with high crosslinking degree, encapsulant with high adhesive strength (neutral silicone rubber), toughened glass with high light transmittance and high strength, etc.
3. Reasonable packaging technology
4. The rigorous work style of employees;
Because solar cells belong to high-tech products, some details in the production process, such as wearing gloves without gloves, uneven application of reagents, graffiti and other inconspicuous problems, are the enemies that affect the quality of products. Therefore, in addition to formulating reasonable production technology, it is very important for employees to be serious and rigorous.
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Brief introduction of solar cell assembly process;
Here is just a brief introduction to the role of technology to give you a perceptual understanding.
1, battery test:
Because of the randomness of battery chip manufacturing conditions, the produced batteries have different performances, so in order to effectively combine batteries with the same or similar performances, they should be classified according to their performance parameters; Battery testing is to classify batteries by testing their output parameters (current and voltage). In order to improve the utilization rate of batteries, qualified battery components are manufactured.
2. Front welding:
The bus bar is welded to the main grid line on the front (cathode) of the battery. The bus bars are tinned copper bars. The welding machine we use can spot weld the welding strip on the main grid line in the form of multiple points. The welding heat source is an infrared lamp (using the thermal effect of infrared rays). The length of the welding strip is about twice the length of the battery side. The additional welding tape is connected with the back electrode of the back battery piece during back welding.
3. Back connection:
Back welding is to connect 36 batteries in series to form an assembly string. At present, the technology we use is manual. The positioning of the battery mainly depends on a film plate with 36 grooves to place the battery. The size of the groove corresponds to the size of the battery, and the position of the groove has been designed. Modules of different specifications use different templates. The operator uses soldering iron and solder wire to weld the front electrode (negative electrode) of the "front battery" to the "rear battery".
4. Laminated laying:
After the back surface is connected in series, after passing the inspection, the component string, glass, cut EVA, glass fiber and back plate are paved according to a certain level and ready for lamination. Glass is pre-coated with a layer of primer to increase the bonding strength between glass and EVA. When laying, ensure the relative position of battery string and glass and other materials, and adjust the distance between batteries to lay a good foundation for lamination. (Laying level: from bottom to top: tempered glass, EVA, battery, EVA, glass fiber, backboard).
5. Lamination of components:
Put the battery into a laminator, pump out the air in the module by vacuumizing, and then heat and melt the EVA to bond the battery, glass and backplane together; Finally, cool that extracted component. The lamination process is a key step in module production, and the lamination temperature and time are determined according to the properties of EVA. When we use fast curing EVA, the lamination cycle time is about 25 minutes. The curing temperature is 65438 050℃.
6. Finishing:
EVA will melt and solidify under pressure to form burrs during bonding, so it should be cut off after bonding.
7. Framework:
Similar to putting a frame on the glass; The aluminum frame is installed on the glass module to increase the strength of the module, further seal the battery module and prolong the service life of the battery. The gap between the frame and the glass assembly is filled with silicone. Frames are connected by corner keys.
8, welding junction box:
Weld a box at the lead on the back of the assembly to facilitate the connection between the battery and other equipment or batteries.
9. high voltage test:
High voltage test refers to applying a certain voltage between the frame of the module and the electrode leads to test the withstand voltage and insulation strength of the module, so as to ensure that the module will not be damaged under harsh natural conditions (lightning, etc.). ).
10, component testing:
The purpose of the test is to calibrate the output power of the battery, test its output characteristics and determine the quality level of the module. At present, standard test conditions (STC) are mainly used to simulate sunlight. Generally speaking, the test time required for the battery panel is about 7-8 seconds.
Design steps of solar cell array
1. Calculate the 24-hour consumption capacity p of the load.
P=H/V
V- rated power supply of load
2. Choose the sunshine time T(H) every day.
3. Calculate the working current of the solar array.
IP=P( 1+Q)/T
Q—— According to the surplus coefficient in rainy season, q = 0.2 1 ~ 1.00.
4. Determine the battery floating charge voltage VF.
The floating voltages of Ni-Cd (GN) and lead-acid (CS) batteries are 1.4 ~ 1.6V and 2.2V respectively.
5. Solar cell temperature compensation voltage.
VT=2. 1/430(T-25)VF
6. Calculate the working voltage VP of the solar cell array.
VP=VF+VD+VT
Where VD = 0.5 ~ 0.7
Approximately equal to VF
7. What is the output power WP of the solar array? Flat solar panels.
WP=IP×UP
8. According to the combination series table of VP and WP in the silicon panel, determine the number of series blocks and parallel groups of standard specifications.
Solar cell development market
New type solar cell
At present, the average efficiency of mass-produced monocrystalline and polycrystalline solar cells on the market is about 15%, that is, this kind of solar cells can only convert incident solar energy into 15% of available electric energy, and the remaining 85% is wasted as useless heat energy. So strictly speaking, the current solar cells are also a kind of "waste of energy". Of course, in theory, as long as the energy exchange between carriers and phonons in solar cells can be effectively suppressed, in other words, the energy release within or between energy bands of carriers can be effectively suppressed, the generation of useless heat energy in solar cells can be effectively avoided, and the efficiency of solar cells can be greatly improved, even ultra-efficient operation can be realized. However, such a simple theoretical idea can be realized in different ways in practical technology. The technical development of ultra-efficient solar cells (the third generation solar cells) not only tries to break through its physical limitations by using novel module structure design, but also may achieve the purpose of greatly improving the conversion efficiency because of the introduction of new materials.
Thin-film solar cells include amorphous silicon solar cells, CdTe and CIGS (copper India gallium selenium) cells. Although the conversion efficiency of most mass-produced thin-film solar cells can't compete with crystalline silicon solar cells, their low manufacturing costs still make them occupy a place in the market, and their market share will continue to grow in the future.
Dye-sensitized solar cell
Dye-sensitized solar cell (DSSC) is a brand-new solar cell recently developed. DSsC is also known as Gr? Tzel cell, because Gr built it in 199 1 The structure published by tzel et al. is different from that of ordinary photovoltaic cells. Its substrate is usually glass or transparent flexible polymer foil. A layer of transparent conductive oxide (TCO) is usually made of FTO(SnO2:F), and then a layer of porous nano-sized TiO2 particles (about 10 micron thick) is grown on the glass. Then, a layer of dye is coated and attached to the TiO2 particles. In general, ruthenium polypyridine complexes are used as dyes. In addition to glass and TCO, the upper electrode is plated with a layer of platinum as a catalyst for electrolyte reaction, and an electrolyte containing iodide/triiodide is injected between the two electrodes. Although the highest conversion efficiency of DSC battery is about 12% (29% in theory), the manufacturing process is simple, so it is generally believed that the production cost will be greatly reduced, and the electricity fee per kilowatt hour will also be reduced.
Series battery
Laminated battery is a novel battery with original structure, and the structural design of optimizing absorption efficiency is realized by designing multiple layers of solar cells with different energy gaps. At present, according to theoretical calculation, if more layers of batteries are placed in the structure, the battery efficiency will be gradually improved, and even the conversion efficiency can reach 50%.
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Transparent solar cell
According to a recent report by the American Physicist Organization Network, scientists from Brookhaven National Laboratory and Los Alamos National Laboratory of the US Department of Energy have developed a new type of transparent film, which can absorb light and convert it into electric energy in a large area. This thin film is made of semiconductor and fullerene and has a micro-honeycomb structure. Related research was published in the latest issue of Material Chemistry, and the paper said that this technology can be used to develop transparent solar panels, and even windows that can generate electricity can be made of this material. This material consists of a semiconductor polymer doped with carbon fullerenes. Under strictly controlled conditions, the material can be self-assembled from a micron-sized hexagonal structure into a plane covered with a few millimeters of microporous structure.
Mircea Cartwright, a physical chemist in the Center for Multifunctional Nanomaterials at Brookhaven National Laboratory in the United States, who is in charge of this research, said that although this kind of honeycomb film is made by a process similar to that of traditional polymer materials (such as polystyrene), it is the first time that semiconductors and fullerenes are used as raw materials, and it can absorb light and generate charges.
According to reports, the material can keep its appearance transparent because the polymer chain is only closely connected with the edge of the hexagon, while the structure of the rest is relatively simple, and it is thinner and thinner from the connection point. This structure has the function of connection, and at the same time, it has a strong ability to absorb light, which is also conducive to conducting current, while other parts are relatively thin and more transparent, mainly playing the role of light transmission.
Researchers weave this honeycomb film in a very unique way: first, add a very thin layer of micron-sized water droplets to a solution containing polymers and fullerenes. These water droplets will self-assemble into a large array after contacting with polymer solution, and a large hexagonal honeycomb plane will be formed when the solvent is completely evaporated. In addition, the researchers found that the formation of polymer is closely related to the evaporation rate of solvent, which in turn determines the charge transfer rate of the final material. The slower the solvent evaporation, the tighter the polymer structure and the faster the charge transfer speed.
"This is a low-cost and remarkable preparation method with great potential from laboratory to large-scale commercial production." Cartwright said.
Through scanning probe electron microscope and fluorescence scanning microscope, the researchers confirmed the uniformity of the new material honeycomb structure, and tested the optical characteristics and charge generation of different parts (edges, centers and nodes).
Cartwright said: "Our work has made people have a deeper understanding of the optical characteristics of honeycomb structures. Next, we plan to apply this material to the manufacture of transparent flexible solar cells and other equipment to promote this honeycomb film to enter the practical stage as soon as possible. "