In the manufacturing process of photovoltaic cells, temperature control is a key factor affecting the efficiency and stability of the cells.
The following are the temperature control methods and key points of each main production link:
1. Diffusion bonding
- Function: Formation of PN junction on the surface of the silicon wafer by high-temperature diffusion.
- Temperature range: usually between 800~1000°C, depending on the diffusion source (e.g. phosphorus diffusion or boron diffusion).
- Control Method:
- Tubular diffusion furnace with high-precision temperature control system (e.g. PID control) to keep temperature fluctuations within ±1°C.
- Silicon wafers are loaded through quartz boats and heated evenly to avoid local temperature differences.
- Real-time monitoring of the furnace temperature and regulation of the reaction rate by gas flow (e.g., oxygen, nitrogen).
2. Etching process
- Function: Remove excess material from edges or surfaces and optimize the cell structure.
- Temperature range:
- Wet etching: The temperature of the solution is usually controlled at 20~30°C to avoid overly violent reactions.
- Dry etching (such as plasma etching): The temperature of the equipment cavity should be stable at 50~150°C to prevent damage to the silicon wafer.
- Control Method:
- Wet etching uses a thermostatic water bath or heat exchanger to maintain the temperature of the solution.
- Dry etching regulates the temperature of the chamber through the machine's built-in temperature control system, such as water cooling or resistance heating.
3. Thin film deposition (e.g. PECVD)
- Function: Deposition of anti-reflective coatings or passivation layers (e.g., SiNx) on the surface of silicon wafers.
- Temperature range: low temperature process (200~400°C) to avoid secondary damage to silicon wafers due to high temperature.
- Control Method:
- Use a plasma-enhanced chemical vapor deposition (PECVD) device to control the reaction temperature by RF power and gas flow.
- Infrared temperature measurement is used in the cavity to monitor the temperature of the silicon wafer in real time to ensure uniformity.
4. Screen printing and sintering
- Function: Printing electrode slurry and forming conductive contact by sintering.
- Temperature range:
- Drying stage: 100~150°C to remove solvents.
- Sintering stage: The peak temperature is about 750~850°C to ensure the fusion of slurry and silicon wafer.
- Control Method:
- Use a chain sintering furnace with sectional temperature control (e.g. preheating, sintering, cooling zone).
- Uniform heating by infrared heating or hot air circulation to avoid electrode detachment or wafer warping.
5. Ambient temperature control
- Clean room requirements: The production workshop needs to maintain constant temperature and humidity (such as temperature 22±2°C, humidity 40~60%) to prevent silicon wafer oxidation or equipment accuracy degradation.
- Equipment cooling: High-power equipment (e.g., diffusion furnaces, PECVD) needs to be equipped with a cooling water system to avoid overheating.
6. Monitoring and Feedback
- Sensors: Use thermocouples, infrared thermometers, or fiber optic sensors to monitor critical node temperatures in real time.
- Automation system: Closed-loop control is achieved by dynamically adjusting heating/cooling parameters through PLC or DCS systems.
Key challenges and solutions
- Uniformity issues: independent temperature control in multiple temperature zones and optimized gas flow design (e.g. gas distribution in diffusion furnaces).
- Rapid ramp and temperature: Use high-efficiency thermally conductive materials such as graphite boats, or optimize the furnace structure to reduce thermal inertia.
- Different process compatibility: For example, the tunneling oxide layer of TOPCon cells needs to be prepared at low temperature (about 300°C), which needs to match the temperature control capacity of the equipment.
Through the above refined temperature control strategies, the conversion efficiency and yield of photovoltaic cells can be significantly improved. In actual production, the temperature parameters need to be adjusted according to the specific process (such as PERC, HJT, TOPCon).