Silver clad copper, the key driving force for cost reduction in HJT batteries

1、 The global photovoltaic market has vast development space

（1） The photovoltaic clean energy market has great potential, and the newly installed capacity continues to grow

1. Green and sustainable development are urgently needed, and the photovoltaic industry has a vast market

The global economic development and environment are under pressure, and the importance of renewable energy is becoming increasingly prominent. With the rapid development of the global economy, the consumption of energy is also increasing, and the global environment is also under tremendous pressure. At the same time, many energy consuming countries are also facing the dilemma of insufficient sustainable supply capacity of conventional fossil fuels. Renewable energy is increasingly valued by countries around the world, and many countries are actively researching and developing the utilization of renewable energy. Green and sustainable development are urgently needed.
The background of accelerating carbon reduction is relatively clear, and the advantages of photovoltaic power generation are obvious. Internationally, since the Paris Agreement came into effect, a new era of climate governance has begun worldwide. As the world's largest energy producer and consumer, China actively shoulders the responsibility of a major power while developing, and proposed the "dual carbon" goal in 2020. In the context of "dual carbon", renewable energy has become an important direction for energy structure reform in various countries. Compared with new power generation technologies such as wind power, biomass power, and hydropower, photovoltaic power generation is the most sustainable and ideal renewable energy generation technology. Photovoltaic power generation, with its advantages of cleanliness, safety, and easy accessibility, has become an important component of global renewable energy development and utilization.

The proportion of photovoltaic power generation is gradually increasing, with great potential for development. At present, the global renewable energy generation accounts for only about 29% of the total global power generation, of which photovoltaic power generation accounts for about 3% of the global total power generation, equivalent to about 10.34% of the renewable energy generation. There is still significant room for improvement in the proportion of photovoltaic power generation.

CPIA predicts that the global installed capacity of photovoltaics will continue to grow rapidly. Photovoltaic power generation has become a clean, low-carbon, and cost-effective form of energy in many countries. In 2021, driven by favorable factors such as the continuous decline in photovoltaic power generation costs and global green recovery, it is predicted that the global photovoltaic market will continue to grow rapidly. Driven by the transition to clean energy in multiple countries, CPIA expects global photovoltaic installed capacity to continue to grow from 2020 to 2025, with an annual increase of approximately 210-260GW. In an optimistic scenario, it is expected that there will be an additional installed capacity of 330GW by 2030.

China leads in both newly added photovoltaic installed capacity and cumulative photovoltaic installed capacity. In 2020, China's newly installed photovoltaic capacity reached 48.2GW, ranking first in the world for eight consecutive years. With the continuous growth of new installed capacity every year, China's cumulative installed capacity reached 253GW in 2020, ranking first in the world for six consecutive years.

The National Energy Administration has clear goals and actively implements safeguard policies.

（2） The introduction of the photovoltaic industry chain and N-type batteries in photovoltaic direct conversion utilizes the photovoltaic effect of semiconductors. When silicon wafers are exposed to light, the charge distribution changes, generating an electromotive force that converts photons into electrons and light energy into electrical energy. The industrial chain that focuses on the application and development of silicon materials, namely the photovoltaic industry.

Solar cells are typical two terminal devices composed of silicon wafers, passivation films, and metal electrodes. As the core material of the photovoltaic industry chain, the quality of silicon wafers directly affects the photovoltaic conversion efficiency, and photovoltaic silver paste is a key material for preparing metal electrodes for solar cells. Solar cell manufacturers use screen printing technology to print photovoltaic silver paste on both sides of silicon wafers, which are then dried and sintered to form the two end electrodes of solar cells.

According to their location and function, photovoltaic silver paste can be divided into two types: front silver paste and back silver paste.

The upstream link of the photovoltaic industry chain is silicon wafers andPhotovoltaic silver pasteThe development of solar cells is closely related to the overall development of the photovoltaic industry, jointly determining the conversion efficiency and cost of solar cells. There are two types of solar cells: P-type cells and N-type cells, with the difference being in the raw material silicon wafer and cell preparation technology. P-type silicon wafers are made by doping boron elements into silicon materials, while N-type silicon wafers are made by doping phosphorus elements into silicon materials. Given the advantages of N-type batteries, scientists and technicians generally believe that they are the next generation of battery technology. Currently, the main technological breakthroughs are to continue improving the photoelectric conversion efficiency and reducing costs.

2、 The transformation of the photovoltaic industry triggered by HJT

（1） PERC technology is approaching the ceiling, and HJT conversion efficiency continues to make new breakthroughs

The photovoltaic industry is experiencing rapid technological iteration, and HJT is expected to become the third-generation technology. Photovoltaic cells have undergone multiple iterations: from conventional aluminum backplate BSF cells (1st generation) to PERC cells (2nd generation), PERC TOPCon cells (2.5th generation), HJT cells (3rd generation), HBC cells (4th generation), and so on. With each iteration of new technologies, the photovoltaic cell industry will usher in a new round of expansion cycle, which in turn will drive the demand for battery equipment representing new technologies. At present, solar cells are in the transition stage from Generation 2.5 to Generation 3, and heterojunction (HJT) is regarded as the next mainstream technology after PERC, which is currently a hot topic of concern. The essence of battery cell technology iteration is to replace the original battery cells with a new generation of battery cells with better cost-effectiveness, which is reflected in conversion efficiency and manufacturing and usage costs. At present, PERC cells are mainly popular, but PERC has become very mature and the conversion efficiency of cells is close to the ceiling. At this time, developing the next generation of cell technology has become a top priority for scientific research and development. HJT batteries have gained widespread attention and sustained investment in the industry due to their high photoelectric conversion efficiency and cost reduction potential, and are expected to become the mainstream technology of the third generation.

The photoelectric conversion efficiency of HJT is astonishing, and in recent years, many enterprises have continuously made new breakthroughs. In 2020, Maiwei, Zhongwei, Junshi, and Dongfang Risheng all had HJT conversion efficiency certification records. Maiwei Corporation used its independently developed HJT heterojunction high-efficiency battery production equipment and SunDrive's electroplating process to achieve a photoelectric conversion efficiency of 25.54% on full-size single-crystal HJT cells, setting a new world record! HJT efficiency continues to make new breakthroughs, but its cost is much higher than PERC cells. According to CPIA, the cost per watt excluding tax for PERC cells is 0.72 yuan, while for HJT cells it reaches 0.9 yuan. In addition to production equipment, from the perspective of raw materials, the cost difference is mainly reflected in the silver paste consumption. The silver paste consumption of M6 cells is 90mg/piece for PERC cells, while the double-sided silver paste consumption of HJT cells is 202mg/piece, which is twice that of PERC cells. At the same time, the silicon wafer cost and depreciation cost of HJT cells are slightly higher than those of PERC cells, and they also require a certain amount of target material, while PERC cells do not. In terms of equipment cost, although the price of HJT equipment has significantly decreased, the total price of GW level is still more than twice that of PERC. The high equipment price has also increased the manufacturing cost of corresponding machine materials and spare parts.

In terms of overall efficiency and cost, we believe that HJT has great potential in the future. At present, while continuously breaking through the efficiency of photoelectric conversion, the cost is also constantly decreasing. In addition, with government support, the dual carbon national policy, and the continued favorable future of new energy, these will promote the development of HJT, and the trend is relatively clear. The team led by Shen Honglie from China Southern Airlines predicts that the development of heterojunction battery technology in China will enter a rapid stage from 2020 to 2023. Domestic equipment will gradually take shape, leading to a reduction in overall equipment investment, a certain scale of raw materials will gradually form, resulting in a decrease in prices, and the process will gradually become mastered and mature. The production line scale will be increased to the GW level. In 2023 and beyond, China's heterojunction batteries will enter a mature and explosive period. With the cooperation of equipment manufacturers, the localization of equipment will lead to a significant decrease in production line investment; Auxiliary materials（Low temperature silver pasteThe localization of materials such as target materials and the formation of economies of scale can significantly reduce non silicon costs and continue to solve the problem of cost reduction and efficiency improvement.

（2） HJTVsTOPCon, the battle for leading N-type battery manufacturers

TOPCon and HJT are two different directions of the new generation battery, both with excellent performance, but there are certain differences in many aspects. TOPCon and HJT are both N-type cells. While HJT continues to break through the photoelectric conversion efficiency, TOPCon has also achieved conversion efficiency far higher than PERC cells and has a cost advantage.

1. HJT preparation process is simple

From the preparation process, HJT only requires 6 steps (4 steps before the core steps), with a simple industrial structure and low labor costs. The cleaning and velvet making process requires high cleanliness and is also relatively complex; More PECVD equipment is required for amorphous silicon deposition, and the coating speed is low; Double sided PVD coated TCO film is the focus of the process, which directly determines the final conversion efficiency; Double sided silver wire printing and sintering use low-temperature silver paste, which has lower activity and therefore requires a larger amount than high-temperature silver paste; Light regeneration and testing are essential steps. HJT's production line is not compatible with traditional PERC and requires higher investment costs. The total steps of TOPCon are 12-13, and the industrial structure is relatively complex. TOPCon has added some steps on the basis of PERC, and the overall process and equipment are not significantly different from PERC. The most obvious difference is that TOPCon uses double-sided high-temperature silver paste, which has a slightly higher conversion efficiency than PERC.

The biggest advantage of TOPCon technology compared to HJT technology is its good compatibility with PERC cell production lines. HJT cells require the use of brand new equipment due to their unique cell structure. Compared to PERC, TOPCon has undergone three major changes and added three new equipment components: boron diffusion, tunneling oxidation, and amorphous silicon (LPCVD or PECVD), as well as de plating and cleaning. According to SOLARZOOM, the current PERC cell production capacity in the industry is over 250GW, and some newer production lines have reserved space for upgrading TOPCon cells. 2. HJT conversion efficiency is higher than TOPCon

The conversion efficiency of traditional PERC cells is approaching the ceiling, but HJT and TOPCon are constantly making new breakthroughs. According to CPIA, by the end of 2020, the average conversion efficiency of TOPCon reached 23.5%, while the average conversion efficiency of HJT reached 23.8%, both of which showed significant improvement compared to 2019. It is expected that after 2020, there will be new breakthroughs in the average and highest conversion efficiency between HJT and TOPCon each year, with HJT's average conversion efficiency slightly higher than TOPCon's. By 2030, HJT's average conversion efficiency will reach 25.9%, and TOPCon's will reach 25.7%. It is expected that the average conversion efficiency of HJT will remain slightly higher than TOPCon, which is also one of HJT's main advantages. In the future, with the reduction of production costs and the improvement of yield, N-type batteries will be one of the main development directions of battery technology.

3. HJT market penetration rate is expected to surpass TOPCon

Compared to traditional PERC, the relative cost of HJT and TOPCon is higher, and the scale of mass production is still relatively small. CPIA predicts that their market share will gradually increase. According to CPIA, the combined market share of HJT and TOPCon in 2020 was approximately 3.5%, a slight increase from 2019. But both HJT and TOPCon have entered a rapid development stage. With the resolution of efficiency and cost issues, production capacity will continue to increase and enter a mature explosive period, gradually replacing traditional PERC. CPIA predicts that by 2030, HJT's market share will reach about 32%, TOPCon's market share will reach about 24%, and the market share of both types of batteries will continue to rise. Before 2026, it is expected that TOPCon's market share will be slightly higher than HJT's, but HJT's growth rate will be higher than TOPCon's. By 2026, the market share of the two types of batteries will be equal, and then HJT's market share will be higher than TOPCon, gradually becoming the mainstream of the market. 4. Summary of battery technology characteristics

HJT batteries have been developed for about 30 years, but it is not until recent years that there has been a qualitative leap in conversion efficiency. In comparison, The technological development period of TOPCon is relatively short, and both HJT batteries and TOPCon batteries have certain technical advantages and technical difficulties to be overcome.

Overall, both types of N-type batteries have their own advantages and disadvantages, but with the progress of scientific research, the conversion efficiency of the two batteries will continue to improve and the cost will continue to decrease. In the short term, the production cost of HJT is higher than TOPCon, and it is expected that in the next 2-3 years, there will be a situation where TOPCon and HJT technology routes will develop together. In the long run, the conversion efficiency of HJT will improve even more. As costs decrease and technology becomes more mature, HJT may become the mainstream in the market. According to Global Photovoltaic, Chairman Zhou Jian of Maiwei is more optimistic about the expansion and advantages of heterojunction production capacity. It is expected that by 2022, due to the introduction of microcrystals, there will be a significant gap between heterojunction and TOPCon.

（3） HJT's production capacity is gradually being invested, and the production scale is expanding day by day

Since 2020, domestic high-capacity heterojunction production lines have been gradually built, and the production scale is also expanding day by day. At present, the domestically built production capacity is 2950MW, and the waiting capacity is 51.95GW. It is expected that another 5GW production line will be put into construction before the end of this year, namely Huasheng 2GW, Jingang Glass 1.2GW, and Aikang 2GW. Looking at the HJT battery construction plan, in addition to some old manufacturers, there are also many new enterprises that see strong demand for photovoltaics in the future and hope to enter the photovoltaic track with HJT. With the continuous investment and construction of production capacity, this year will also be a crucial year for realizing the cost reduction of heterojunctions.

3、 Low temperature silver paste for HJT core auxiliary materials

（1） Raw materials and preparation of photovoltaic silver paste

Photovoltaic silver paste is a basic material mainly made of silver powder, which is a viscous paste composed of high-purity silver powder, glass oxide, organic materials, and other mechanical mixtures. It is generally divided into conductive silver paste, resistance silver paste, and electric melting silver paste, of which more than 90% is used for conductivity. Therefore, photovoltaic silver paste is also known as conductive silver paste. The requirements for raw materials in photovoltaic silver paste are very strict. The purity, particle size, and shape of silver powder, as well as the selection and ratio of glass oxide and organic raw materials, are all preparation difficulties. Each part of the raw material has different effects on the performance, but they will jointly affect the conductivity. In terms of cost, silver powder accounts for 98.2%, while the sum of glass oxide and organic raw materials is less than 2%. The high cost of silver powder is partly due to the high price of metallic silver, and partly due to the high process requirements of silver powder. Over 50% of the global market is monopolized by Japan's DOWA, and reducing the cost of silver powder is also the key to HJT's cost reduction. The main production process of photovoltaic silver paste includes: batching, mixing and stirring, grinding, filtering, testing, etc. Photovoltaic silver paste is a formula based product, and any parameter changes in the formula will affect the performance of the silver paste. Therefore, precise ingredients are the basis for subsequent steps. Mixing and stirring ensure that the raw materials are in full contact, while grinding is the core process to achieve sufficient mixing of the slurry, thereby achieving the requirements of uniform structure, consistent composition, and standard fineness of the slurry. Filtering is used to control the range of product fineness, while finished product testing and rework are guarantees of performance.

1. Production requirements

At present, photovoltaic silver paste is divided into two types: high-temperature silver paste and low-temperature silver paste, with the main difference being the process temperature. Traditional P-type cells and N-type TOPCon useHigh-temperature silver paste， HJT can only use low-temperature silver paste. HJT battery is a new battery process technology that uses thin film technology to produce PN nodes, anti reflection layers, and conductive layers on crystalline silicon substrates. The process temperature of the entire battery manufacturing process does not exceed 400 ℃. High temperature silver paste forming requires a high temperature of over 700 ℃. If high-temperature silver paste is used as the positive and negative electrodes of HJT batteries, it will cause significant damage to their thin film structure. Low temperature silver paste not only requires a different curing temperature from high-temperature silver paste, but also has other requirements. According to Moore's Photovoltaic, the requirements for low-temperature silver paste are: ① electrode forming temperature below 200 ℃; ② The resistivity of the electrode body is below 10-5 Ω cm; ③ The electrode does not need to form ohmic contact with silicon, but the contact with the TCO conductive layer needs to be sufficiently low; ④ Can withstand the brazing temperature impact of 200-350 ℃ during battery string welding, and the welding tension should be greater than 1N/mm; ⑤ Under long-term illumination conditions, maintain the stability of electrode resistance and ensure chemical stability with component packaging materials. Based on the above technical requirements, the HJT industry currently uses resin cured low-temperature silver paste to make the positive/negative electrodes of batteries. 2. Market share and supply situation

Given that only HJT cells use low-temperature silver paste in photovoltaic cells, the market share of HJT cells also reflects the proportion of low-temperature silver paste.

Compared to high-temperature silver paste, low-temperature silver paste has insufficient production capacity and stronger monopoly. According to Moore Photovoltaic, KE Group in Japan has a market share of over 90% in the international market for low-temperature silver paste. KE focuses on developing low-temperature silver paste, especially the high conductivity low-temperature silver paste used in HJT batteries. Among KE's shareholders are the organic resin giant Daiichi Kogyo and the world's largest manufacturer of silver powder, DOWA. They have significant advantages in raw materials, resulting in excellent low-temperature silver paste performance. Nanotech from Japan, DuPont, Helix, and Henkel from the United States have all developed HJT low-temperature silver paste products, but currently face the problem of a relatively small market share and unclear technical characteristics of related products.

Low temperature silver paste is regarded as the last link in the photovoltaic industry chain to achieve localization, and some silver paste giants in the domestic market are also constantly making new breakthroughs.

Dike Corporation has launched the DK61 series low-temperature silver paste, continuously increasing research and development investment, and actively laying out the development and industrialization of HJT battery low-temperature conductive silver paste products.

Suzhou Gude: Significant progress has been made in the research and development of low-temperature silver paste, and a new generation of efficient, low volume, and fast printing low-temperature silver paste has been developed. The test results on the client side show that the new product can maintain the advantage of conversion efficiency while reducing consumption by nearly 30% and printing speed by 20%. At present, the product has entered the reliability testing phase.

Juhe Corporation: According to Moore Photovoltaic, HJT low-temperature silver paste products have been evaluated and recognized by multiple domestic HJT battery customers, and have entered mass production and supply. Juhe Corporation is also continuously developing new HJT low-temperature silver paste products with narrow line width, high-speed printing, low-temperature rapid curing, low body resistivity, and low cost.

3. Trend of consumption of low-temperature silver paste in HJT batteries

HJT batteries are double-sidedLow temperature silver pasteThe consumption of silver paste is huge and the price is expensive, which is also one of the reasons for the high cost of HJT. According to CPIA, the consumption of double-sided low-temperature silver paste for HJT batteries in 2020 was approximately 223.3mg/sheet, a year-on-year decrease of 25.6%. Although the consumption of silver paste is still high, there has been a significant increase and improvement in 2020 compared to 2019. At present, various technological upgrades are being carried out to reduce the consumption of low-temperature silver paste in order to lower the production cost of HJT batteries. It is expected that by 2030, the consumption of low-temperature silver paste in HJT will decrease to 135mg/sheet, a decrease of 39.5% compared to 2020. 4、 HJT cost reduction: Non silicon link cost reduction becomes key

Silicon wafers are the core material of HJT batteries, accounting for approximately 45% of the cost structure of HJT. Excluding the cost of silicon wafers, silver paste is the core auxiliary material in non silicon materials, accounting for about 59%. HJT silicon wafer substrates use N-type silicon wafers, which are slightly more expensive than P-type silicon wafers. The cost reduction space for silicon wafers in the photovoltaic industry is limited, and we hope to achieve silicon wafer thinning. However, non silicon materials have great potential for cost reduction, and the cost of silver paste is the top priority in reducing non silicon costs. The high cost of silver paste is due to its large usage and high price, so there are two main directions for cost reduction. One is to reduce the amount of low-temperature silver paste, with the idea of reducing the gate line area without affecting the conversion efficiency. Specific methods include multi main gate technology (MBB), transfer printing, etc. The second is to reduce the use of precious metal silver. The idea is to reduce the amount of silver powder without affecting the conversion efficiency, and replace a part of the silver powder with base metals. Specific methods include electroplating copper and silver coated copper.

（1） Reduce the amount of silver paste used

1. Mainstream technology: multi main gate

Multi main gate technology (MBB) usually refers to the use of six or more main gate lines, with an increase in the number and thinness of main gate lines, which can reduce the shading area and reduce resistance losses, improve battery efficiency, and enhance the optical utilization of the solder strip area, further improving the power output of the component. As the width of the main and fine gate lines decreases, the silver paste consumption can be significantly reduced. Therefore, multi main gate batteries also have the advantages of low silver paste consumption and less susceptibility to hidden cracks. The metallization process of multi main gate batteries and the interconnection process between battery cells are the technical keys of multi main gate components.

The development process of multi main grid technology is intuitively reflected in the increase in the number of main grids. Before 2010, the initial solar cells were mainly 2BB, and since 2010, the basic pace has been technological progress every 2-3 years. Starting from 2010, manufacturers gradually entered 3BB; At the beginning of 2013, the manufacturer gradually switched from 3BB to 4BB; Around 2015, the manufacturer gradually switched from 4BB to 5BB; In 2017, some major manufacturers began to launch multi gate battery cells, and multi gate soon became the mainstream in the market.

The multi gate technology has a wide range of applications, including traditional P-type batteries and N-type batteries. The upgrade of multi main grid technology is mainly reflected in the replacement of component string welding equipment. For battery equipment, the changes are not significant, mainly requiring the replacement and adjustment of screen printing equipment and the improvement of the accuracy of sorting equipment. The multi gate technology is widely used in HJT, reducing the consumption of low-temperature silver paste from 350mg/piece at 4BB to 200-250mg/piece. At present, 9BB and 12BB have become mainstream technologies in metallization processes, which are expected to further reduce the amount of silver paste used.

With the gradual maturity of multi gate technology, based on it, Maiwei and Huasheng jointly launched SMBB (Super MBB), which is expected to reduce the consumption of HJT silver paste to 120mg/piece.

On the basis of multiple main gates, in addition to optimized SMBB, we have also developed new gate line designs from Junshi and masterless gate (SMWT) technology from Meyerberg. The common feature of the above technologies is contact metallization technology, which adopts screen printing process and optimizes the design of the main gate and fine gate. Non contact metallization technology is no longer limited to screen printing process, and further optimization of silver paste consumption and gate line morphology is achieved through various innovative electrode production methods. Although it is not a mainstream technology at present, it is still under research and development.

2. New Technology: Transfer Printing

Laser transfer printing is a type of paste printing technology, not only for silver paste, but also for other pastes. There are over 100 fine grids on the front of the battery cell, and laser transfer printing does not require contact with the battery surface during processing, which can reduce the fragmentation rate, achieve finer grids, reduce silver consumption costs, and improve efficiency.

Di'er Laser's solar cell laser process equipment has the highest global market share, and its laser transfer technology is at the forefront of the international market. Before laser transfer printing, it was mainly demonstrated for a long time on PERC, and there were also experiments on TOPCON with significant results. There are also HJT layouts in the company laboratory, all of which are undergoing research and development. Laser transfer technology has been experimentally demonstrated in the customer segment and is currently being intensively imported into engineering. We look forward to delivering the entire line to the customer next year. The research and development technology of the company's high-speed PTP laser printing technology aims to achieve better aspect ratio and finer grid line printing through laser transfer printing technology, improve the conversion efficiency of solar cells, save the consumption of printing paste, and meet the production needs of different sizes of 166-220mm solar cells. It is expected to achieve results in June next year.

As a leading traditional screen printing equipment, Maiwei is also actively developing transfer printing technology, with transfer printing, secondary printing, and inkjet printing all in the layout. Maiwei is developing a special transfer printing equipment that uses a transfer printing method instead of screen printing, which can achieve finer grid lines and better morphology. Simultaneously develop a thin film that can transfer silver paste from solar cells. The film is made of special materials and processes, and uses a special transfer process, combined with a high-precision CCD system, to accurately transfer silver paste from the film to the solar cell.

It is expected that the multi main grid technology of screen printing will remain mainstream in the next five years, while transfer printing is also constantly achieving new results, which is expected to save more silver paste for HJT batteries. （2） Reduce the use of precious metal silver

1. Copper electroplating technology

HJT electroplating copper technology is a new electrode preparation technology that uses the principle of electrolysis to deposit copper on the surface of a conductive layer. It is mainly based on the seed layer grid line method instead of screen printing to produce electrodes. Generally, silver containing electroplating solution is used, followed by copper coating to reduce the amount of silver paste used, or copper coating is used completely to replace silver paste, making the cost more competitive. On the basis of the silver electrode process, electroplating copper replaces double-sided silver wire printing with a series of steps such as PVD seed layer plating, and then sintering to form a copper electrode. Overall, the process flow is more complex than before and requires more equipment.

The advantages and disadvantages of electroplating copper technology are very obvious, with the biggest advantage being the use of copper instead of some or all of the metallic silver. The material cost is low, and double-sided metallization can be completed simultaneously. The disadvantage is that the process flow is longer than traditional screen printing technology, requiring more equipment and labor costs. In addition, copper is prone to oxidation at high temperatures, and its chemical properties are difficult to control. There are many harmful chemicals in the plating solution, making it difficult to handle and resulting in higher environmental costs. With the tightening of environmental protection policies, the approval of plating projects will become more difficult. In terms of efficiency, SunDrive's electroplating process collaborated with Maiwei's equipment to achieve a photoelectric conversion efficiency of 25.54% on full-size single-crystal HJT cells, setting a new world record. Overall, compared to other technologies, electroplated copper currently has limited competitiveness.

2. Silver coated copper technology

The above cost reduction techniques are an optimization and upgrade of the metallization process, and are also of great significance for the cost reduction and optimization of silver paste materials themselves. After optimizing the silver paste material and combining it with the metallization process, the cost of silver paste can be further reduced, thereby achieving sustained cost reduction for HJT. On the one hand, the cost reduction of silver paste materials lies in achieving production scale and localization. Domestic silver paste giants such as Dike Corporation, Suzhou Gude, and Juhe Corporation are actively expanding their production scale; On the other hand, it lies in optimizing material composition, reducing material costs, and developing new slurries. Silver coated copper is a representative technology in this regard.

Silver powder accounts for over 98% of the total cost of low-temperature silver paste, so the key to cost reduction in low-temperature silver paste is to reduce the amount of silver powder used. DOWA's copper powder production technology has certain advantages. Inorganic coatings, organic coatings, and thin film processing can meet various needs. Copper powder is mainly used for external electrode applications of multi-layer ceramic capacitors. However, copper as a substitute material for silver is receiving increasing attention in the industry. DOWA is also actively developing silver coated copper powder on the basis of its silver powder and copper powder to replace silver powder and achieve cost reduction. KE and DOWA's silver coated copper technology are at the forefront of the international market.

Copper has good conductivity and thermal conductivity, and is inexpensive. Compared with silver, it has a huge price advantage. However, the main disadvantage of copper is that its chemical properties are not stable enough, and its antioxidant capacity is poor, especially in humid and high-temperature environments, which cannot meet the requirements of photovoltaic pastes. The purpose of developing silver coated copper ultrafine powder is to replace silver powder: it can meet the requirements of photovoltaic paste and has a huge price competitive advantage. The essence of silver coated copper cost reduction lies in replacing a portion of silver in the silver paste with base metal copper, covering copper with silver, and continuously adjusting the doping ratio of silver and copper through experiments to improve the photoelectric conversion efficiency, while ensuring a certain efficiency and reducing the cost of silver paste. Silver coated copper powder is prepared based on ultrafine copper powder products, and the quality of ultrafine copper powder directly affects the performance of the final silver coated copper. In terms of technical parameters, the resistance and density of silver coated copper powder are between silver powder and copper powder, and the resistance decreases with increasing pressure, while the specific surface area of silver coated copper powder is higher than that of silver powder and copper powder. The particle size of silver coated copper powder ranges from 2 microns to 4 microns, and the shape of silver coated copper particles can be spherical or flaky. According to SMM, the morphology of copper particles has a significant impact on coating. The more nano and atomically arranged the coating particles, the denser the coating layer, which can provide higher temperature resistance. The finer the coating layer, the closer the particles are to the color of copper, which can be used to determine the quality of the coating. And the higher the sintering temperature, the thicker the coating layer needs to be, that is, the higher the silver content is required. Silver coated copper is prone to oxidation and failure in traditional PERC high-temperature processes, while HJT's low-temperature process can suppress copper oxidation. Therefore, silver coated copper has great potential for promotion and application in HJT.

Based on the above HJT cost reduction technologies, we believe that multi gate technology and transfer printing technology have good application prospects in reducing silver paste consumption, and domestic equipment is constantly making optimization breakthroughs; In terms of reducing the use of precious metal silver, we believe that silver in copper technology has broad prospects and is relatively easy to achieve mass production.