Flexible amorphous silicon thin film 18650 2000mah battery technology

　　In the past few decades, the continuous rapid development of human economic activities has caused a rapid increase in electricity demand. A 18650 2000mah battery is a semiconductor device that uses the photovoltaic effect to directly convert solar energy into electrical energy. It can easily be connected to the grid for power generation or used as an independent energy source. As we all know, 18650 2000mah battery power generation has many advantages, such as safety and reliability, no noise, no pollution, energy is available everywhere, no need to consume fuel, no mechanical rotating parts, low failure rate, easy maintenance, can be unattended, and can be of any size , can be easily combined with buildings, etc. These advantages are beyond the reach of conventional power generation.

　　At present, 18650 2000mah battery power generation has occupied an irreplaceable position in the fields of aerospace, communications and microelectronics, but it accounts for a small proportion in the overall energy structure of society. The main reason is that the cost of 18650 2000mah batterys is high. To make it truly an energy system components, the cost must be significantly reduced. Thin film 18650 2000mah batterys have greater advantages than crystalline silicon (monocrystalline or polycrystalline) 18650 2000mah batterys in terms of cost reduction. First, after achieving thin film, expensive semiconductor materials can be greatly saved; second, the material preparation and battery of thin film cells It is formed at the same time, thus saving many processes; third, thin film 18650 2000mah batterys adopt low-temperature process technology, which is not only conducive to energy saving and consumption reduction, but also facilitates the use of cheap substrates (glass, stainless steel, etc.). To this end, since the 1970s, countries around the world have invested heavily in formulating plans, organizing teams, and launching a research craze on thin-film 18650 2000mah batterys. Over the past thirty years, great progress has been made in research, development and application.

　　Thin film 18650 2000mah batterys mainly involve amorphous silicon (a-Si:H), copper indium gallium selenide (Cu(In, Ga)Se2, CIGS) and cadmium telluride (CdTe) photovoltaic cells and integrated components, which are mainly discussed in this article It is the most mature amorphous silicon 18650 2000mah battery currently commercialized. Thin film 18650 2000mah batterys are divided into two categories: hard substrates and flexible substrates. The so-called flexible substrate 18650 2000mah batterys refer to cells made on flexible materials (such as stainless steel, polyester film). Compared with hard substrate cells such as flat crystalline silicon and glass substrate amorphous silicon, its biggest feature is Lightweight, foldable and unbreakable. For example, the American Uni-Solar company uses stainless steel as the substrate. The thickness of stainless steel is only 127um, and it has excellent softness. It can be curled, cut, and pasted at will, even if it is bent into a small radius, hundreds of times. Curling, battery performance will not change. For amorphous silicon 18650 2000mah batterys prepared with high molecular polymer polyimide as a flexible substrate, the total thickness of the device is about 100um (including the encapsulation layer), and the power-to-weight ratio can reach more than 500W/Kg, which is higher than that of amorphous silicon 18650 2000mah batterys based on stainless steel substrates. Silicon cells are nearly ten times more powerful and are the lightest 18650 2000mah batterys in the world. From the perspective of the preparation process, since the battery with this structure is manufactured using the roll-to-roll process, it facilitates large-area continuous production, has great potential for cost reduction, and is highly competitive.

　　Flexible substrate 18650 2000mah batterys can be placed on the top of streamlined cars, on uneven surfaces such as the cabins of sailboats, rowing boats, and motorboats, and on the roofs and exterior walls of buildings such as houses. In addition, because flexible thin film batteries have a high mass specific power (500W/kg) and are flexible, they are very suitable for use on the surface of stratospheric airships for earth observation, and have bright prospects for use in special applications.

　　In recent years, the integration of photovoltaics and buildings (BIpV) promoted abroad has greatly promoted the development of photovoltaic grid-connected systems. Photovoltaic systems installed on urban buildings are usually connected to the public grid. Grid-connected photovoltaic systems do not need to be equipped with batteries, which saves investment and are not limited by the state of charge of the batteries. They can make full use of the power generated by the photovoltaic system; photovoltaic arrays are generally installed on idle roofs or exterior walls, without occupying additional land. , which is especially important for urban buildings with expensive land; summer is the peak season for electricity consumption, which also happens to be the period when the amount of sunshine is the largest and the photovoltaic system generates the most power, which can play a peak-shaving role in the power grid; the photovoltaic array absorbs solar energy and converts it into electrical energy. It greatly reduces the overall outdoor temperature, reduces the heat gain of the wall and the cooling load of the indoor air conditioner, so it can also play a role in building energy conservation.

　　The development of BIpV is currently a major research hotspot in the world for large-scale use of photovoltaic technology to generate electricity. Western developed countries are actively pursuing it as a key project. In addition to installing photovoltaic panels on roofs, products that install photovoltaic cells in tiles have been introduced. In addition, foreign countries are also studying photovoltaic wall structures (pVWALL), which combine photovoltaic systems with building exterior walls. It can be expected that the combination of photovoltaics and buildings will be one of the most important fields in future photovoltaic applications. Its development prospects are very broad and it has huge market potential. Flexible substrate thin film batteries will undoubtedly play an important role in it.

　　Structure of two flexible substrate thin film 18650 2000mah batterys

　　Flexible substrate 18650 2000mah batterys can adopt single-junction or multi-junction structures. Single-junction structures are rarely used due to their poor stability and low efficiency. Multi-junction and stacked 18650 2000mah batterys with good stability and high efficiency are the development direction of flexible substrate 18650 2000mah batterys. Currently, triple-junction 18650 2000mah battery structures are mostly used. In a triple-junction 18650 2000mah battery, each cell is made up of three semiconductor junctions stacked on top of each other: the bottom cell absorbs red light; the middle cell absorbs green light; the top cell absorbs blue light; a wide range of responses to the sunlight spectrum improves cell efficiency. The essential. The structure of the stainless steel substrate, triple-junction amorphous silicon germanium 18650 2000mah battery of Uni-Solar Company in the United States is shown in Figure 3. Its small-area cell efficiency currently reaches 14.6%.

　　Current status of three-flexible substrate thin film 18650 2000mah batterys at home and abroad

　　The stable efficiencies of current commercial amorphous silicon cells are 4%~5%, 6%~7%, and 7%~8% for single junction, double junction, and triple junction respectively. The main units in the world engaged in the development and production of flexible substrate thin-film 18650 2000mah batterys are United Solar in the United States, VHF-technologies in Europe, and Sharp and Sanyo in Japan.

　　The focus of the U.S. photovoltaic program is the "Thin Film Partnership Program", which focuses on the research of cheap and efficient thin film 18650 2000mah batterys. It is expected that by around 2020, the cost of photovoltaic power generation is expected to compete with fuel power generation (equivalent to a cell efficiency of 15% and a cost per square meter of ≤ US$50 ).

　　The United Solar Systems company in the United States is a joint venture between Energy Conversion Devices, Inc. (ECD) and N.V. Bekaert S.A (BESS Europe). In 2003, it established a simultaneous deposition of 6 rolls of stainless steel coils, a triple-junction laminated amorphous silicon cell production line, with an annual output of 30MW and an initial efficiency of and stable efficiency reached 14.6% and 12.6% respectively. It was 50MW in 2006, 100MW in 2007, and the target in 2010 is 300MW.

　　The University of Toledo in the United States is a world leader in the field of flexible substrate amorphous silicon 18650 2000mah batterys. The initial efficiency of its single-junction amorphous silicon germanium cell laboratory reached 13%. Their technical team participated in the establishment of MWOE and Xunlight companies, and We are actively planning for greater production capacity.

　　Japan is also at the forefront of the world in research on flexible substrate 18650 2000mah batterys. In Japan, Sharp, Sanyo, TDK, and Fuji have invested a lot of manpower and material resources in the development of flexible substrate amorphous silicon 18650 2000mah batterys, and have built multiple megawatt-level polyester film flexible battery production lines. Sanyo was the first company to use flexible substrate amorphous 18650 2000mah batterys as energy source on an unmanned solar aircraft, completing a flight across the American continent, demonstrating the huge potential of flexible amorphous thin film 18650 2000mah batterys as an energy source for aircraft. The amorphous silicon 18650 2000mah batterys prepared by Sharp Company and TDK Company on polyester film can currently produce modules with an area of 286cm2, with an efficiency of 8.1%, and the efficiency of small-area cells has reached 11.1%. Fuji's a-Si/a-SiGe stacked cell has a stable efficiency of 9%. It has established a factory in Kumamoto, Japan, and its output of plastic substrate amorphous silicon cells reached 15MW in 2006.

　　The European Union has teamed up with multiple research institutions in its member states, including Neuchatel University, VHF-technologies, Roth & Rau, etc. to carry out joint research on polyester film substrate flexible batteries, and has now achieved small-volume production lines. The EU launched the "FLEXCELLENCE" project on October 1, 2005, for a period of three years. The goal is to develop equipment and processes for roll-to-roll production of high-efficiency thin film battery components, build a flexible battery production line of more than 50 MW, and hope to Production costs are controlled at 0.5 euros per watt. According to reports in 2007, the current polyester film substrate amorphous silicon stacked cell laboratory efficiency of Neuchatel University has reached 10.8%, and the annual production capacity of VHF-technologies is 25MW.

　　The research progress of flexible substrate thin film batteries in my country is slow. Harbin Chrona Company developed an amorphous silicon single-junction thin-film battery on a flexible polyimide substrate in the mid-1990s. The initial efficiency of the battery was 4.63% and the power-to-weight ratio was 231.5W/kg. However, there has been little progress since then. In recent years, Nankai University has made certain progress in research on flexible substrate amorphous silicon thin film batteries. They obtained a single junction thin film battery on a 0.115cm2 polyimide substrate with an initial efficiency of 4.84% and a power-to-weight ratio of 341W/kg.

　　In terms of the industrialization of flexible substrate batteries, Tianjin Jinneng Battery Co., Ltd. is currently building a 6MW amorphous silicon flexible battery production line, and the 30MW production line has begun project demonstration. Xinjiang Tianfu Photovoltaic Light Display Co., Ltd. is building a 1MW amorphous silicon flexible battery. The production line is planned to build 8MW in the future. Both companies are expected to have high battery costs because their equipment and technology are imported from abroad. In general, China currently has the technical foundation for the development of amorphous silicon thin film batteries, but research on flexible substrates is still in its infancy, and the gap with foreign countries is large.

　　Preparation of four flexible substrate thin film 18650 2000mah batterys

　　The following is a brief introduction to the roll-to-roll (rolltoroll) production process, taking the stainless steel flexible substrate three-junction amorphous silicon 18650 2000mah battery of the American Uni-Solar Company as an example.

　　Load the rolled stainless steel belt (magnetic) into a special cleaning machine, use the roll-to-roll method to transport the steel belt, and clean and dry both surfaces of the steel belt at the same time. First, metal and metal oxide layers are deposited by magnetron sputtering to enhance the reflectivity of the substrate. Plasma chemical vapor deposition (pECVD) is then used to deposit an amorphous silicon layer to form a stacked 18650 2000mah battery structure, which is the most critical process step in the entire manufacturing process. For triple-junction amorphous silicon 18650 2000mah batterys, 9 layers of silicon-based films need to be continuously deposited on the surface of the prepared back reflector, including 3 p-I-N junction sub-cells. Unique atmosphere isolation needs to be designed between each separate reaction chamber. chamber to prevent gas cross-contamination between adjacent reaction chambers. After the deposition of the silicon-based film is completed, indium tin oxide (ITO), a transparent conductive oxide layer, needs to be deposited on the top of the battery as an anti-reflective layer for incident light. Then the grid lines need to be arranged on the light incident side, and according to the size and shape of the final battery, cutting, electrode joining, battery cutting and battery interconnection are performed to form a battery component with certain parameters. The production line has an annual output of 30MW and a cost of US$60 million. It is 90 meters long and 3 meters high, with a stainless steel substrate of 127μm thickness (2.6km long and 36cm wide).

　　Using rolltoroll technology to prepare large-area flexible substrate amorphous silicon 18650 2000mah batterys, there are the following key technical issues that need to be solved: high-speed deposition of amorphous silicon thin films; uniformity during large-area thin film growth; development of gas isolation devices between reaction chambers ;Real-time monitoring and diagnosis, etc. The development of the entire rolltoroll production line is a reflection of a country's comprehensive industrial strength and foundation.

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