Cell screen printing is a technique that utilizes a stencil to repeatedly reproduce the same print on a surface. In the context of photovoltaic (PV) solar cells, screen printing is commonly used for metallization, a process that applies conductive metal pastes to the silicon cell to form electrical contacts.
The Process in Solar Cell Manufacturing
Screen printing for solar cells typically involves the application of three different types of metallization pastes onto the silicon (c-Si) cell:
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Front Side Metallization: This usually involves printing silver (Ag) paste to form the front electrical contacts. The paste is designed to fire through the anti-reflection coating (ARC) during a subsequent high-temperature process.
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Back Side Metallization (Aluminum): An aluminum (Al) paste is printed on the back surface of the cell. During firing, the aluminum diffuses into the silicon, forming a back surface field (BSF) that enhances the cell's efficiency.
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Back Side Metallization (Silver/Aluminum): A silver/aluminum (Ag/Al) paste is also printed on the back, typically in specific regions, to provide good solderability for interconnection between cells in a solar panel.
Key Aspects of Screen Printing
- Stencil Creation: A mesh screen is coated with a photosensitive emulsion. A stencil with the desired pattern is placed on the screen and exposed to UV light. The unexposed areas of the emulsion are washed away, creating the stencil.
- Paste Application: The screen is placed on the solar cell, and metallization paste is spread across the screen. A squeegee is then used to force the paste through the open areas of the stencil onto the cell surface.
- Firing: After printing, the cells undergo a high-temperature firing process. This process allows the metal to make ohmic contact with the silicon, forming the electrical contacts. It also allows the aluminum to diffuse into the silicon, forming the BSF.
Advantages of Screen Printing in Solar Cell Manufacturing
- High Throughput: Screen printing is a relatively fast process, making it suitable for mass production of solar cells.
- Cost-Effective: The equipment and materials required for screen printing are relatively inexpensive compared to other metallization techniques.
- Simple Process: The process is relatively simple and easy to control.
- Versatile: Screen printing can be used to apply a variety of different metallization pastes.
In summary, cell screen printing is a stencil-based printing method widely used in the solar cell industry to apply metal contacts onto silicon wafers, crucial for electricity generation.
