一、 Overview
Photovoltaic silver paste is mainly composed of high-purity silver powder, glass oxides, and organic carriers, and is mainly used to estimate the current generated by the front and back electrodes of photovoltaic cells and silicon-based photovoltaics.
Photovoltaic silver paste is located in the middle of the entire industry chain, with silver powder, glass oxide, and organic carrier enterprises upstream and photovoltaic cell manufacturers downstream. Among them, silver powder is a conductive phase, mainly used for conductivity. The quality of silver powder directly affects the body resistance and contact resistance of electrode materials; Glass oxide is a bonding phase that serves as a conductive film layer medium, connecting the conductive phase and substrate. If its composition ratio and overall content in the silver paste are too high, it will lead to a decrease in the conductivity of the silver paste. If it is too low, it will not penetrate into the passivation layer and silicon substrate to form conductive contact; Organic carriers are composed of organic matter and some liquids, mainly used as conductive and adhesive carriers to control the fluidity of the slurry. The supply of photovoltaic silver paste is mainly influenced by the production of midstream enterprises and the supply of upstream silver powder, while the demand is influenced by the production of downstream silicon-based photovoltaic cells.
Photovoltaic silver paste can be divided into front silver paste and back silver paste according to different positions. Among them, the functionality of the back silver paste is weak, and the technical threshold is relatively low. The main demand in the industry is cost reduction, and it is now basically possible to achieve localization; The preparation of positive silver paste is difficult and an important component of photovoltaic cells, mainly used for collecting current.
According to the technical route and process flow classification, photovoltaic silver paste can be divided into high-temperature silver paste and low-temperature silver paste. High temperature silver paste is made by sintering silver powder, glass oxide, and other solvents in an environment above 500 ℃, while low-temperature silver paste is made by mixing silver powder, resin, and other solvents in a relatively low temperature environment of 200-250 ℃. Currently, P-type batteries and N-type TOPCon batteries mainly use high-temperature silver paste. Due to the high hydrogen content of amorphous silicon films in HJT batteries, the production process temperature is required to not exceed 250 ℃, which promotes the research and industrialization of low-temperature silver paste technology.
二、 Production process
Positive silver paste is a key material for preparing metal electrodes for solar cells, which directly affects the photovoltaic conversion efficiency of solar cells.
Positive silver paste belongs to formula products. Due to the wide variety and rapid changes in solar cell technology categories, different manufacturers choose different technical paths and production processes, so the performance requirements for the suitable positive silver paste are also different. Therefore, any parameter adjustment on the positive silver paste formula will affect the compatibility with the production process of the battery cell manufacturer and the photoelectric conversion efficiency of the battery cell.
The production process of positive silver paste is to mix silver powder, glass powder (or resin), organic and other substances, then put them into mechanical equipment for mixing, stirring, grinding, controlling the stirring and grinding process parameters, filtering out the silver paste, inspecting product performance, packaging, and warehousing.
1.Ingredients
Ingredients refer to the precise weighing of various raw materials required for the final product based on the product formula produced in that batch.
2. Mixing and stirring
Mixing and stirring refers to mixing qualified glass oxides, silver powder, and organic raw materials according to the proportion in the formula, and then using a mixer to stir the mixture. By setting the speed, time, and stability parameters of the mixer, the slurry is fully and uniformly mixed.
3. Grinding
The grinding process uses a three roll grinder to grind the stirred slurry. The specific working principle is as follows: by adjusting the gap between the rollers and the rotation speed of different rollers, the slurry particles passing through are subjected to rolling pressure, shearing, and dispersion, thereby opening up the agglomeration of slurry particles, allowing the slurry to be fully mixed, and achieving the requirements of uniform slurry organization, consistent composition, and standard fineness.
The grinding process is the core process, and the quality of the product is closely related to it. Different products present different states on the equipment, and correspondingly, the grinding process parameter settings for different products are also different. The roller clearance, roller speed, and grinding time during the grinding process are usually key parameter settings for this process.
4. Filtering
The filtration process mainly involves using a negative pressure filtration system to screen the ground material according to the process requirements, in order to intercept materials with particle sizes larger than the standard requirements, ensuring consistent product fineness, and ensuring the performance requirements of the finished slurry during client printing use.
5. Testing
Test and verify the product according to the product standards. Product testing includes testing the physical parameters of the slurry itself, such as fineness, solid content, viscosity, etc. At the same time, the application performance of the slurry can be tested according to batch requirements, such as resistivity, printability, other electrical performance indicators, etc. Products can only be packaged and stored after passing the inspection, and those that fail the inspection need to be reworked.
三、 Cost and Investment
1. Cost composition
In the production cost of photovoltaic silver paste, direct materials (silver powder, glass phase, organic phase, etc.) account for 99.41% (including 4.65% of material sales cost), labor cost accounts for 0.24%, manufacturing cost accounts for 0.28%, and logistics related expenses account for 0.07%. It can be seen that the material cost in the production process of silver slurry accounts for the largest proportion, while the labor and manufacturing fuel and power costs account for a relatively small proportion. Among the material costs, the cost of silver powder accounts for more than 90%.
Taking Juhe Materials, a listed company, as an example, from 2019 to 2022, the company's silver powder accounted for over 97% of the raw material procurement cost, and the total proportion of the three main materials was about 99.64%.
As can be seen from the above, silver powder is the most important raw material for producing photovoltaic slurries, and its morphology, particle size, dispersibility, and compacted density all have a significant impact on its electrical performance, contact, and flowability. According to the different appearance of silver powder, it can be divided into spherical silver powder, sheet-like silver powder, and branched structure silver powder. Different shapes of silver powder will cause differences in the sintered thick film structure of silver paste, thereby affecting the performance of battery cells.
The silver powder used in the production of photovoltaic silver paste in China is currently mainly imported, among which DOWA from Japan is the main supplier of silver powder imported from China. DOWA silver powder has smaller particle size, better dispersibility, better organic coating effect, and more stable quality.
The high investment in research and development of silver powder and the high technical barriers it faces are important factors restricting the marketization of domestic silver powder in China. The main domestic silver powder enterprises include Suzhou Simete and Ningbo Jingxin.
2. Silver slurry consumption per unit
According to research feedback from experts on Knowledge Planet, the current mainstream batteries 182 and 210 in the market have different unit consumption from different manufacturers. Longi has its own components and the unit consumption is relatively low. Tongwei has higher quality requirements and higher unit consumption. 182PERC, with a consumption of over 50 milligrams per unit, 210PERC, with a consumption of over 60 milligrams per unit, can reach up to 70 milligrams for high consumption. TOPCon also uses silver paste on the back, which is 1/3182 of the front TOPCon. Overall, not including the back, only the front is considered, around 105 milliliters
Grams, 210TOPCon, about 180 milligrams. 210HJT, the front and back low-temperature silver paste added together is about 200 milligrams.
Converted to single watt consumption, the consumption of PERC silver slurry is 6-8mg/w, TOPCon silver slurry is 10-13mg/w, and HJT silver slurry is about 16mg/w.
In terms of processing fees: The current processing fee for PERC silver is about 500 yuan/kg, and the TOPCon processing fee is 300+yuan/kg higher than that for PERC silver. The processing fee for HJT low-temperature silver paste is 1000-1500 yuan/kg higher than that for PERC positive silver paste.
3. Investment scale
According to the relevant announcements released by Suzhou Guzheng, Dike Co., Ltd., and Juju Co., Ltd., due to different factors such as production technology, process, site, and market of each company, the required investment scale for investing 500-1700 tons of photovoltaic silver paste production capacity is between 150 million and 270 million yuan, corresponding to a single ton of photovoltaic silver paste investment cost of about 160000-530000 yuan.
Among them, land and construction projects, equipment procurement and installation projects account for the highest proportion, accounting for about 32.9-56.5% of the overall investment in production line construction, and equipment procurement amounts account for about 24.1-36.3% of the overall investment. The main equipment is metalization printing production lines, three roll machines, etc.
Glass powder: an indispensable key element in the manufacturing of solar cells
Crystal silicon solar cells are currently the most widely used photovoltaic power generation technology, and silver paste is one of the essential materials in the manufacturing of solar cells. Silver paste is usually coated on the positive electrode surface of solar cells to provide electronic transmission, reflection, and protection functions.
Crystal silicon solar panels
Silver paste
In silver paste, glass powder is an important additive, whose main function is to increase the adhesion of silver paste and enhance its conductivity. At the same time, glass powder can also improve the fluidity of silver paste, promote its uniform distribution on the surface of solar cells, and thus improve the photovoltaic conversion efficiency of solar cells.
Silver paste
Silver paste is composed of silver powder, glass powder, and organic carriers, with a glass powder content typically ranging from 2% to 5%. Although glass powder has a low content, it plays a crucial role in silver paste, playing functions such as corroding silicon nitride layers, forming electrodes, and bridging electronic transport. In the manufacturing of solar cells, it is very important to choose high-quality silver paste on the front side, as it directly affects the performance and lifespan of solar cells.
Glass powder
Performance of glass powder and silver paste
Glass powder needs to be balanced and adjusted under different conditions, with important functions such as bonding silver powder, reducing sintering temperature, corroding the anti reflective layer on the upper part of the silicon substrate, and forming Ohmic contact. Especially in the manufacturing of solar cells, the front glass powder system of silver paste needs to have appropriate softening temperature and corrosion ability to ensure good adhesion between silver paste and silicon substrate, as well as excellent performance in electrical performance and photoelectric conversion efficiency.
Silver paste
As an inorganic bonding phase in the positive silver paste, glass powder needs to meet the following requirements:
1. Suitable softening temperature: Glass powder needs to have a suitable softening temperature to melt and form a good bond with silver powder and silicon substrate during the sintering process.
2. Able to corrode the anti reflective layer: Glass powder needs to have a certain corrosion ability to melt and corrode the anti reflective layer on the upper part of the silicon substrate, in order to achieve good contact between silver powder and the silicon substrate.
3. Can reduce sintering temperature: Glass powder can be used as a sintering aid to lower sintering temperature and improve product manufacturing efficiency.
4. Uniform particle size distribution: The particle size distribution of glass powder needs to be uniform to ensure uniform dispersion in the preparation of silver paste.
Solar cells
Lead-free glass powder
At present, lead-free has become a trend in the development of modern glass powder. Among them, the sol-gel method is a common method to prepare lead-free glass powder for solar cells.
Glass powder
Compared with the traditional leaded glass powder, the lead-free doped glass powder prepared by the sol-gel method shows advantages in many aspects. First, the sol gel method can fully mix the raw materials and form a stable transparent sol system, thus realizing the preparation process of uniform composition and high purity. Secondly, in the doping process, the sol gel method can reduce the content of dopant to a very low level, so as to achieve the goal of easy doping. In addition, the lead-free doped glass powder prepared by the sol-gel method is easy to refine, which is conducive to improving the material performance. At the same time, the particle size of the powder is smaller, which is more conducive to processing and application.
