With the improvement of industrial automation, both solar cell production workshops and photovoltaic module production workshops are gradually introducing semi-automatic or fully automated production lines. The production lines require fewer and fewer employees, but the quality requirements for technical personnel are increasing. The higher, they need to understand each equipment and be able to ensure the stable and reliable operation of the equipment, so as to ensure the yield and quality of component products. The key production equipment commonly used in the production of photovoltaic modules includes cutting equipment, glass washing machines, welding equipment, vacuum lamination equipment, etc.
During the production process of photovoltaic modules, inspection is usually required at key nodes, and only after passing the test can they flow into the next process in order to improve the yield. The main testing instruments are solar simulation tester and crack tester. The solar simulation tester is used to test the electrical performance parameters of the components, so as to perform power evaluation and classification of the components. Crack testers are used to detect battery defects inside modules.
The cutting equipment used in the photovoltaic industry mainly includes diamond cutting equipment and laser dicing machines. Due to the higher efficiency of laser cutting, many factories now use laser dicing machines to cut solar cells and silicon wafers.
- Principle of laser scribing
The laser has the characteristics of high brightness, high directivity, high monochromaticity and high coherence. After the laser beam is focused, it can generate a high temperature of thousands of degrees Celsius at the focus, and it can process almost all materials. Laser scribing is to focus the laser beam on the surface of silicon, tin, arsenic and other materials, and through high temperature, the surface of the material is melted and evaporated to form a groove, because stress concentration will be formed at the groove, so it is easy to remove the material along the groove. Disconnect neatly. Laser scribing is a non-contact process, so scribing crystalline silicon solar cells with lasers can better prevent damage and pollution, and improve the yield of scribing.
- Equipment introduction
Laser dicing machine is generally composed of laser crystal, power supply system, cooling system, optical scanning system, focusing system, vacuum pump, control system, workbench, computer, etc. There are power supply, vacuum pump, cooling water switch button and current adjustment button on the console And so on, there are air holes on the worktable, and the air holes are connected with the vacuum pump. After the vacuum pump is turned on, the solar cells are adsorbed and fixed on the console, and it is not easy to produce displacement during the cutting process.
When using the dicing machine to cut the battery, first turn on the laser dicing machine and its matching computer, put the solar cell to be cut face down on the cutting table, and put it in a good position, then open the relevant software in the computer, according to the required battery After designing the line according to the size, input the travel distance between the X-axis and the Y-axis direction. After previewing and determining the line, adjust the current to the appropriate current for cutting.
- Cutting key process control points
In order to ensure the least loss of the battery during the cutting process and ensure that the yield of subsequent components is not affected, the following key process control points need to be grasped during the cutting process:
(1) The slicing direction is usually cut from the back of the battery to avoid cutting through the p-n junction on the front side, resulting in a short circuit between the positive and negative electrodes of the battery;
(2) The alignment accuracy is determined according to the size of the battery to be cut. Usually, the alignment accuracy of a 156mm×156mm battery half-cut needs to be less than 0.2mm;
(3) Cutting depth The cutting depth is usually controlled at about 60% of the battery thickness, and the cutting depth is mainly controlled by adjusting the laser power and laser scribing speed parameters on the equipment;
(4) The flatness of the cutting edge should ensure that the battery is close to the working panel, and the laser head should be well focused to ensure the flatness of the cutting edge, avoid defects such as V-shaped missing corners, and reduce the occurrence of cracks and fragments;
(5) The slicing fragmentation rate is from feeding, dicing, breaking to blanking, each operation may cause fragmentation, so it is necessary to control the yield rate of each step;
(6) Capacity Under the premise of ensuring the quality of slicing, the slicing capacity is controlled by adjusting the laser power and scribing speed.
In addition, when operating the cutting machine, you need to pay attention to the following issues:
(1) When slicing, it is necessary to select the appropriate scribing parameters according to the size, thickness, warpage and capacity requirements of the cut battery, especially the settings of laser power and scribing speed. The output power of the laser is large and the energy of the laser beam is strong, which can directly cut the battery, but it is easy to cause a short circuit between the positive and negative electrodes of the battery. On the contrary, if the power output is small, the cutting depth is not enough, and when the battery is broken along the scratch, it is easy to break the battery. When the laser power is constant, the laser slicing speed is too slow, the cutting depth will increase, and long-term high temperature will cause great damage to the battery; but if the cutting speed is too fast, the scratches will be shallow, and the battery will be easily broken;
(2) The travel route of the laser beam is determined by the computer setting. When setting the coordinates, a slight error will completely change the laser beam route. Therefore, before cutting the battery, you can use a low-power beam to walk along the set route, and after confirming that the route is correct, increase the laser power for slicing;
(3) Generally speaking, the laser dicing machine can only cut along the X axis and the Y axis direction, and it is more convenient to cut the square battery. When it is required to cut the solar cell into a triangle or other shape, the angle must be calculated before cutting, and by changing the orientation of the battery placement, the line that needs to be cut is in the X or Y direction;
(4) When cutting different solar cells, if the thickness of the two cells is quite different, when adjusting the laser power, it is necessary to adjust the focal length of the laser beam;
(5) When cutting, the vacuum pump should be turned on, so that the battery is tightly fixed on the work panel, otherwise it will cause uneven cutting;
(6) After cutting, the equipment should be cleaned regularly, especially the laser head, negative pressure nozzle passage and suction cup passage. Otherwise, the presence of dust or uneven adsorption of the battery will easily cause the laser head to lose focus, resulting in different depths of scratches and cuts. Jagged.
Using picosecond laser can effectively improve the yield and incision quality of laser scribing. In order to reduce the damage of the laser to the solar cell as much as possible, some devices now upgrade the pulse width of the laser from nanosecond to picosecond. At present, the industry has begun to use picosecond laser for back slotting of PERC cells and laser drilling of MWT cells. hole.
Read more: The evolution of solar photovoltaics