Abstract: Taking the high-efficiency heterojunction battery as the starting point, the development status of heterojunction battery technology is expounded. Three different battery metallization technologies of screen printing technology, electroplating technology and inkjet printing technology are introduced, and the different methods are analyzed. The advantages and disadvantages of the preparation of junction electrodes, and the prospects for the future low-cost, high-efficiency heterojunction battery electrode metallization technology. 0 Preface The sustainable development of energy and environment has become a hot issue of global concern. Photovoltaic power generation has advantages that are unmatched by traditional energy sources. It realizes the direct conversion of solar energy into electrical energy and is the most ideal and sustainable development of green energy. So how to make full use of solar energy, improve the photoelectric conversion efficiency of solar cells, and reduce the cost of solar cells, has become the ultimate goal of scientific researchers. In the process of technological innovation of high-efficiency solar cells, heterojunction batteries are hailed as the most likely high-efficiency N-type batteries for large-scale industrial applications in the future, and it is expected to achieve parity Internet access around 2020. However, the current high cost has also kept many companies on the sidelines. How to reduce the manufacturing cost of solar cells while ensuring high efficiency has become a key research topic carried out by research institutions and enterprises in the industry. In the process of preparing a heterojunction battery, the battery metallization process is one of the key steps to determine the battery efficiency and battery cost. The metal electrode must have a high bonding strength and low contact resistance with the silicon interface, and also Provides a high-conductance path for current output. At present, most of the preparation of metal electrodes for commercial crystalline silicon batteries use screen printing technology. However, whether screen printing technology can meet the future market demand for high efficiency and low cost development of heterojunction batteries is questioned. Exploring the metallization technology that matches the heterojunction battery is one of the effective ways to reduce the cost of the battery and improve the photoelectric conversion efficiency of the battery. At present, many research institutions and enterprises have carried out related research and practice, which has laid a technical foundation for the industrial application of high-efficiency heterojunction batteries. 1 Development status of heterojunction battery technology The photovoltaic market at home and abroad is developing rapidly. High-efficiency and low-cost solar cells have become an inevitable direction of the photovoltaic market demand. Heterojunction solar cells have emerged under the guidance of the market environment. The development of heterojunction cells started in the 1960s. In 1968, heterojunction devices combining crystalline silicon and amorphous silicon were realized. In 1974, hydrogenated amorphous silicon was first realized to reduce the defects of amorphous silicon. The junction battery was successfully fabricated for the first time, with an efficiency of 12.3% and an area of ​​only 0.25%. In 1991, Sanyo Corporation of Japan introduced intrinsic amorphous silicon into the heterojunction cell structure for the first time, achieving excellent interface passivation, preparing a battery with an efficiency of 18.1%, and named the battery of this structure as a heterojunction battery. After decades of development of heterojunction battery technology, battery conversion efficiency has been greatly improved. After Panasonic acquired Sanyo in 2013, the announced laboratory efficiency reached 24.7%, and then combined with back-contact technology, the battery efficiency reached 25.6%. According to the latest report in 2016, Japan ’s NEDO R & D organization and Japan ’s Kaneko Company used heterojunction and back contact coupling technology to increase the conversion efficiency of the battery to 26.33%, setting a new world record. At present, 90% of the commercial crystalline silicon batteries on the market use the screen printing process for the preparation of metal electrodes. However, the preparation process of high-efficiency heterojunction batteries is special. The low temperature process is used throughout, which determines that the electrode preparation process is different from traditional . It is an important way to explore the photoelectric conversion efficiency of high-efficiency heterojunction cells by exploring metallization technologies and process design parameters that match with heterojunction cells, and obtaining high-height ratio and low contact resistance metal gates. In addition, in the cost structure of single-sided batteries, silver paste accounts for 10% to 15% of the total battery cost, and heterojunction batteries are double-sided batteries, and the consumption of silver paste is almost twice that of traditional single-sided batteries. Therefore, Finding low-cost alternative metallization materials that match heterojunction batteries, and exploring easy-to-operate metallization technologies have become another important way to reduce the cost of highly efficient heterojunction batteries. 2 Heterojunction battery metallization method The production process of heterojunction batteries mainly includes amorphous silicon layer deposition, conductive film deposition, surface metallization, low temperature sintering and other processes. Surface metallization is one of the most critical links in the manufacturing process of heterojunction batteries. Not only must it ensure a high bond strength and low contact resistance with the silicon interface, but also provide a high conductivity path for current output. The link is one of the main influencing factors of battery photoelectric conversion efficiency and battery cost. With the continuous improvement and innovation of battery manufacturing technology and slurry preparation technology in the photovoltaic industry, new progress has also been made in battery metallization processes. Common crystalline silicon battery metallization technologies include screen printing, electroplating, and inkjet printing. In the traditional screen printing technology and paste performance improvement and application process, other metallization technologies have been improved and developed to varying degrees. 2.1 Screen printing technology In screen printing, the paste is printed on the surface of the battery through a screen printing device. Under high temperature conditions, the metal particles in the paste are melted and connected to each other and the silicon plate is etched to form a reliable bond and electrical contact. At present, the industry generally uses screen printing technology to print battery grid lines or metal electrodes on the battery base material. Compared with other technologies, screen printing technology firstly has relatively simple equipment structure, low cost and easy operation; secondly, the printing process is mature, the production efficiency is high, and it is easy to realize large-scale automated production, which can save time and cost to a certain extent. However, there are several shortcomings in screen printing: one is that the screen is in contact with the substrate (silicon wafer) during the printing process, which is easy to cause damage to the silicon wafer and secondary pollution; the second is that screen printing often causes waste of paste; the third is At present, it is difficult to increase the printing accuracy and the aspect ratio of the printed fine grid, but the high aspect ratio metal gate is the key link to improve the photoelectric conversion efficiency of the battery. In the continuous development of printing technology, the screen printing process has undergone a transition from one printing to many printings. Although the aspect ratio of the grid line has been improved, the efficiency improvement is difficult to control the printing accuracy and grid extension. The quality problem makes little contribution. In the screen printing process, silver paste is the key material used in the metallization process. Traditional crystalline silicon batteries usually use high-temperature sintering to burn out the organic phase of the silver paste, and the surface of the silver powder is melted and sintered with each other to form a very good conductive path. However, the metallization process of the heterojunction battery adopts a low-temperature process, and the process temperature is generally lower than 250 ° C. Low-temperature conductive silver paste must be used. The surface of the silver powder is covered with a protective agent, and the protective agent is connected to the outer layer of the resin. One silver powder unit is transferred to another silver powder unit, which is an important reason why the electrical conductivity of low-temperature solidified silver paste is usually lower than that of sintered silver paste. At present, the low-temperature paste for the production of heterojunction batteries is completely dependent on imports, such as silver paste produced by companies such as DuPont, Henkel, Heraeus, etc. The domestic research work on low-temperature paste is still basically at the experimental exploration stage, low-temperature paste technology Being monopolized by foreign countries, the price is higher, which makes it difficult to reduce the production cost of heterojunction. On the one hand, there are silver electrodes on both sides of the heterojunction battery, which increases the amount of precious metal silver, and the cost is high; on the other hand, the use of screen printing and sintering processes limits the use of thinner silicon wafer substrates and more The design and application of high-efficiency batteries; secondly, the large series resistance loss is an important factor limiting the improvement of the photoelectric conversion efficiency of heterojunction batteries. Therefore, constantly improving screen printing technology, accelerating the development and application of low-temperature pastes in China, and improving the rheology of silver paste have become the direction of screen printing grid technology innovation for a period of time in the future, and also to improve the quality of heterojunction battery products and photoelectric conversion. An effective way of efficiency. 2.2 Electroplating technology Electroplating technology is the process of depositing a thin layer of metal, alloy or composite material on the surface of conductive solid by electrochemical method, which is a special electrolysis process. After the electroplating solution is energized, the metal cations are moved to the surface of the battery by the potential difference and deposited to form a metal plating layer, which is the electrode. In order to ensure low shading area and low conduction resistance, it is required to prepare narrow and thick metal electrodes. Some research experts have proposed a two-layer electrode technology, which is to first prepare a narrow and thin seed layer grid line, and then thicken the seed layer to prepare a conductive layer by electroplating, light induced plating and other methods. This seed layer plus light-induced electroplating can produce high-quality conductive layers, which can not only increase the aspect ratio of the fine grid lines, reduce the resistivity of the fine grid lines, reduce the width of the fine grid lines, increase the light-receiving area of ​​the battery, but also reduce the silver. The amount of pulp used to achieve the purpose of reducing battery costs. The cost of silver electrodes accounts for a large part of battery costs, and it is easy to fluctuate with the price of precious metals. Replacing silver electrodes with copper electrodes can greatly reduce battery costs. The electroplating technology is used to prepare the metal grid line electrode, only the silver-containing plating solution is used, and the nickel / copper / silver three plating layer is selected, or the nickel / copper plating layer is used to make the battery cost competitive by reducing the silver content. The electroplated copper electrode has the advantages of conductivity equivalent to silver and better contact resistance than silver glue, and the use of low temperature process technology has further reduced the electrode line width and increased the light area, which is expected to increase the absolute efficiency of the battery by more than 0.2%. As early as 2009, Suntech Wuxi used Pluto technology to vacuum-evaporate grid lines and then electroplated them to improve the uniformity and aspect ratio of the grid line coatings, and achieved a photoelectric conversion efficiency of 19% for cells, and mass production. Compared with the traditional screen printing technology, the front electrode of the battery using Pluto technology is narrower, which can reduce the light shielding and reduce the contact area with the silicon wafer, reduce the electronic recombination rate of the metal electrode and silicon bonding interface, increase by about 12% Battery output power. In 2013, IMEC used Meco's nickel / copper plating process to achieve a PERC cell conversion efficiency of 20.7%. In July 2014, IMEC applied Meco's nickel / copper / silver coating (three main grid lines) technology to N-type PERT batteries, making the battery conversion efficiency reach a record 21.5%. In March 2015, MacDermid produced narrow copper mesh conductors instead of silver paste by laser etching, coating, thermal annealing and other processes. Among them, the plating layer was 1μm nickel layer, 10-15μm copper layer and 0.2μm silver layer. This process can achieve a gate line width of 30μm and a pull force of 4N, which can reduce the cost of a single cell by 6 cents. In addition, the low temperature operation makes this process applicable to the development of high-efficiency batteries, such as PERC, silicon-based heterojunction, and double-sided batteries. In September 2015, RENA launched the InCellPlateCu platform, which can perform nickel / copper / silver direct plating on silicon substrates, replacing the traditional screen printing process on the front surface of the battery, thereby reducing the unit cost of battery production by 6 cents. RENA has successfully implemented the application of this technology, achieving a conversion rate of 20.8% on Cz-PERC batteries. In November 2015, Kaneka Corporation of Japan announced that the double-sided heterocrystalline silicon solar cell with copper contact metallization achieved a record efficiency of 25.1%, which was verified by the FraunhoferISE (German FraunhoferISE) and plans to Use this technology to build a trial production line. Copper electroplating technology has excellent characteristics such as simple device, low production cost, uniform and dense plating, and good conductivity. In the preparation process of the battery electrode, the width and height of the grid line can be controlled, which can effectively increase the aspect ratio of the grid line, reduce the shadow loss of the grid line, and effectively reduce the contact resistance between the electrode and the PN junction, and the body of the electrode itself. The resistance and the series resistance of the battery improve the photoelectric conversion efficiency of the battery. The electroplating technology has a low process temperature and can be used not only for the production of traditional battery electrodes, but also for the production of heterojunction batteries, N-type double-sided batteries, PERC batteries, and IBC battery electrodes. Among them, the preparation process of the heterojunction battery requires low temperature throughout. The use of electroplating technology in the preparation process of the battery electrode metalization can not only improve the photoelectric conversion efficiency of the battery, but also overcome the shortcomings of the high cost of the heterojunction battery. At present, a technology platform for electroplated copper electrode solar cells has been established in China, and trial production has begun. Modi, Yuanjing, Yujing and other enterprises have also started small-scale production, but the stability and reliability have not reached the mass production standard, and the electroplating metal electrode process is more complicated, the adhesion is poor, and there is a risk of waste liquid pollution to the environment , So the current market share is still very small. However, according to ITRPV's photovoltaic development in 2016, the demand for electroplating technology will increase in the future. By 2025, the market share of electroplating technology will reach 30%, and the market demand is considerable. 2.3 Inkjet printing technology Inkjet printing technology is a non-contact deposition technology with high grid line resolution. Metal nanoparticles or composite metal particle paste is printed on the surface of the battery substrate by an inkjet printer to form a patterned grid line shape to realize the battery. Metallization of gate lines. The principle is that after the metal liquid is sprayed from the spray gun, the metal ions are charged through a charging electrode plate to charge the metal ions with a certain amount of charge. After the metal ions pass through the high-pressure deflection plate, the charged metal ions are deflected and printed to On the cell substrate, crystalline silicon solar cell electrodes are formed, and ions deflected in the opposite direction are collected and reused. In 1988, inkjet printing technology was first applied to the production of crystalline silicon solar cell electrodes. After years of technological development, inkjet printing technology was used to prepare the front grid electrode of crystalline silicon solar cells. The photoelectric conversion efficiency of the battery reached 18.2%. Inkjet printing grid technology can maximize the cost of electrode materials, control the width of metal grid lines, reduce shadow loss and other advantages, and is very popular among researchers around the world. Liu Jining and other studies found that the electrode structure printed by inkjet technology is finer and the aspect ratio is more superior than the traditional screen printed electrode. EbongA and other studies have found that inkjet printing can control the amount of ink required for the grid lines, which can reduce the cost of solar cell grid metallization. However, the inkjet printing technology also has the problem of grid line expansion in practical applications. GizachewYT and others use multiple equal ink volume inkjet printing methods to improve the grid line aspect ratio of silicon solar cells. However, the inkjet printing within 5 times will produce gridline expansion each time, and even the final gridline width reaches a single inkjet printing Double the width, the problem of grid line expansion is prominent. Inkjet printing technology can control the pattern of printed battery electrodes through a computer program to achieve non-contact printing. It has the characteristics of high printing efficiency and low cost, and is suitable for the deposition of flexible substrates. Inkjet printing has higher grid line resolution. Compared with the traditional screen printing process, the gate width formed is less than or equal to 40μm, the aspect ratio is less than or equal to 0.6, and the printing accuracy error is less than 5μm, which ensures good conductivity. At the same time, it has lower contact resistance, can form a finer electrode structure and a higher aspect ratio than traditional screen printing technology, while saving raw material costs, it can further reduce the recombination loss of minority carriers inside the battery , Increase the square resistance, which is also an effective way to improve the photoelectric conversion efficiency of the battery. Inkjet printing belongs to non-contact printing, the chip breaking rate is less than 0.1%, the choice of substrate materials is large, and it is very suitable for thin-film heterojunction batteries The preparation of the grid line can reduce the fragmentation rate of the heterojunction battery printing process, and compared with the traditional screen printing technology, it can eject ink on demand and accurately control the amount of ink, saving the consumption of silver paste and solving the difference Double the silver consumption of the double-sided electrode of the junction battery leads to the problem of excessively high battery material consumption cost. Therefore, the metallization process of preparing the grid of the heterojunction battery by inkjet printing has a good industrialization promotion prospect. At present, the printing electrode grid lines of inkjet printing technology are still in the laboratory research stage. There are few studies on the metallization of photovoltaic cells using inkjet printing technology in the photovoltaic field at home and abroad. There is no industrial application of traditional batteries. The electrode preparation of the battery is being researched and developed by Meyer Burger. 3 High-efficiency N-type heterojunction battery metallization technology application trends At present, many large enterprises and research institutions in the industry believe that heterojunction batteries are the most likely high-efficiency N-type batteries for industrialization in the next few years. They have simple production processes, low process temperature, good stability, high battery efficiency, and low light response. The selected silicon substrate is thin and other excellent features. However, compared with traditional P-type crystalline silicon batteries, the cost of heterojunction batteries is relatively high. At present, Panasonic Corporation of Japan has begun mass production of heterojunction batteries, and some domestic companies have already had the ability to mass produce heterojunction batteries. Some companies are even preparing to build a 1GW heterojunction battery mass production line. The industrialization trend of high-efficiency heterojunction battery is obvious, but its high equipment input and material cost have caused many companies to wander around. How to further reduce the cost of heterojunction batteries and improve the photoelectric conversion efficiency of batteries is worthy of investigation by enterprises and research institutions. The heterojunction battery is a double-sided symmetrical battery, and the consumption of silver paste is twice that of the single-sided battery. Finding low-cost metal grid materials has become an effective way to reduce the cost of heterojunction batteries. Copper metal has good conductivity and low price, and is an ideal material for the metallization of heterojunction battery grid lines. Using electroplating technology, the metal material is replaced by the silver grid line through the photo-induced plating method to realize the metallization preparation of the heterojunction battery grid line, while maintaining high efficiency and reducing the cost of battery material consumption, this technology has become a highly efficient One of the mainstream technologies of junction metallization technology. At the same time, for the heterojunction battery, the inkjet printing metal electrode technology also has obvious advantages, and is considered to be one of the new technologies to replace the traditional screen printing: first of all, its production equipment is simple, fewer masks, high resolution, and low The characteristics of cost and high yield; secondly, the inkjet printing technology can achieve selective deposition of metal electrode materials to reduce the waste of materials, and the battery metallization process is fired at a low temperature process to prevent the degradation of the p-n junction It meets the requirements of low-temperature preparation technology of heterojunction batteries and is suitable for large-area production. In addition, inkjet printing belongs to non-contact printing, computer-controlled, and accurate printing. It can control the gate line finer and the gate line aspect ratio is more superior. Therefore, it is suitable for the preparation of gate line metallization on fragile thin substrates. With the improvement of the efficiency of heterojunction cells, the substrate is gradually becoming thinner. It is very suitable for this technology to complete the preparation of the gate line metallization, which can reduce the production debris rate while ensuring high conversion efficiency and low resistivity. In addition, the printed ink can be silver ink or low-cost copper ink, which can effectively reduce the material cost of the metal electrode of the heterojunction double-sided battery, further reduce the price of the heterojunction battery product, and make the heterojunction in the next few years The large-scale mass production is more competitive in the market. Simple Plastic Faucet,Plastic Bottle Tap,Plastic Beer Faucet,PP Plastic Tap Faucet Cixi Ruisheng Electric Appliance Factory , https://www.rswatertap.com