What is photovoltaic silver paste?

What is photovoltaic silver paste?

Photovoltaic silver paste belongs to a type of electronic conductive paste. The so-called electronic conductive paste is mainly composed of conductive phase, bonding phase, and liquid carrier, and then made into a viscous paste after stirring and rolling. In addition, silver is the most conductive metal and has stable chemical properties. Therefore, about 80% of electronic pastes on the market currently use silver powder as the conductive phase.

Photovoltaic silver paste is mainly a mixture of high-purity silver powder (conductive phase), glass oxide (bonding phase), and organic resin organic solvent (organic carrier), which is formed as a uniform paste after stirring and three roll rolling; In terms of cost composition, silver powder accounts for over 95% of the cost, so the price of silver paste is highly correlated with silver powder.

Structure of Photovoltaic Silver Paste Industry

The photovoltaic silver paste industry is a part of the photovoltaic industry chain, with its upstream consisting of raw materials such as silver powder, glass oxide, and organic materials, and downstream consisting of photovoltaic cell enterprises.

Classification of Photovoltaic Silver Paste

According to the position of silver paste on the battery cell, it is divided into front silver paste and back silver paste. The front silver paste mainly collects and exports photo generated charge carriers, while the back silver paste mainly has a bonding effect (with lower conductivity requirements), so the front silver paste is the main one. According to the temperature at which silver paste is sintered to form conductivity on the substrate, it is divided into high-temperature silver paste (sintering temperature above 500 ℃) and low-temperature silver paste (sintering temperature below 250 ℃). High temperature silver paste is currently the mainstream used on PERC and Topcon, while low-temperature silver paste is mainly used on HJT.

Photovoltaic silver paste process

The main production process of positive silver paste includes: batching, mixing and stirring, grinding, filtering, testing, etc.

1. Batching: Refers to the precise weighing of various raw materials required for the final product based on the formula of the batch produced. Positive silver paste is a formula based product, and any parameter changes in the formula may affect product performance. Therefore, precise ingredients are the foundation for subsequent stages.

2. Mixing and stirring: refers to mixing qualified glass oxides, silver powders, and organic raw materials according to the proportions in the formula, and then using a mixer to stir the mixture. By setting the process parameters such as the speed, time, and stability of the mixer, the slurry is fully and uniformly mixed.

3. Grinding: It is the use of a three roll grinder to grind the mixed slurry. The specific working principle is as follows: by adjusting the gap between the rollers and the speed of different rollers, the particles flowing through the slurry are subjected to rolling, shearing, and dispersion, thereby opening up the agglomeration of slurry particles, allowing the slurry to be fully mixed, and achieving the requirements of uniform structure, consistent composition, and standard fineness of the slurry. 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 parameter settings for the grinding process of different products are also different. The roller gap, roller speed, and grinding time during the grinding process are usually the key parameters set for this process.

4. Filtering: Mainly through the company's independently developed negative pressure filtration system, the ground material is sieved according to process requirements to intercept materials with particle sizes larger than the standard requirements, ensuring consistent fineness of the product and meeting the performance requirements of the finished slurry when used for client-side printing.

5. Testing: Conduct testing and verification of the product according to product standards. Product testing includes physical parameter testing 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. The products can only be packaged and stored after passing the inspection, and those that fail the inspection need to be reworked.