Principle of classification detection
①Category detection design. The solar cell is to receive sunlight irradiation of specific irradiance at a certain temperature, while changing the load of the external circuit, measuring the current I of the load and the voltage U at the cell end, drawing the relationship curve between the two, and then calculating various electrical performance parameters by the computer software system according to the data and curve, and strictly controlling the temperature of the test environment during the measurement process, because when the temperature changes, the carriers in the silicon cell will be When the temperature changes, the current carriers in the wafer will be affected, so that the open-circuit voltage and short-circuit current of the test will be inaccurate. Therefore, the machine should be calibrated from time to time to prevent machine errors from affecting product performance.
②The classification process, the classification and testing machine in operation will transfer the cells to the dark room in the machine, above the dark room there will be simulated sunlight lamps for irradiation, the equipment will simulate the load and test the system for testing, and then the computer will process and analyze the data according to the test and generate the I-U curve in order to visually reflect the performance of the cells.
③ Classification, using the classification inspection machine to classify the specifications of the cells, mainly based on the power generation efficiency of the cells into multiple blocks, the same conversion efficiency of the cells will be placed together, because when the cells are made into modules to ensure that all cells have the same efficiency, which will reduce the energy loss of the modules due to the different efficiency of the cells. The cells with different conversion efficiency are sorted and placed by mechanical arm.
Classification testing technical parameters
① Battery test standard: irradiance is 1000W/m2, temperature is 25℃2℃.
② Main electrical performance parameters.
a. Short-circuit current (Isc): Under the test standard, the output current of the solar cell in the short-circuit state.
b. Open-circuit voltage (UOC): Under the test standard, the terminal voltage of the solar cell in the open-circuit state without load.
c. Maximum output power (Pmax): the power expressed at the point on the I-U curve where the product of current and voltage is maximum.
d. Series resistance (RS): the equivalent resistance of the solar cell when it is connected from the front to the back.
e. Parallel resistance (Rsh): refers to the equivalent resistance inside the solar cell as well as across all the ends of the cell.
f. Conversion efficiency (Ncell): The ratio of output power to incident light power is the conversion efficiency.
g. Filling factor (FF): reflects the variation of the output power of the cell with the load. The fill factor is closely related to the intensity of the incident spectrum, short-circuit current, open-circuit voltage, series resistance and parallel resistance.
3 The effect of temperature on the battery. In the test, the change of temperature has little effect on the short-circuit current, but has a greater effect on the open-circuit voltage. Generally, for every 1°C increase in temperature, the UOC decreases by about 0.4%; the filling factor FF decreases with the rise of temperature due to the relationship of UOC: the output power decreases with the increase of temperature.
④ The effect of light intensity on the cell: ISC and UOC decrease with the decrease of light intensity, among which the change of ISC is especially significant.
Generally speaking, the surface of solar cells made of polycrystalline silicon has crystalline grains; the surface of solar cells made of monocrystalline silicon is uniform.
Crystalline silicon solar cell production line equipment
1 The equipment of crystalline silicon solar cell production line includes cleaning and linting machine, diffusion furnace, plasma etching machine, secondary cleaning machine, shaking dryer, plasma chemical vapor deposition equipment (PECVD), screen printing machine, sintering furnace, quartz tube cleaning machine, tester, heat shrink packaging machine, graphite electrode cleaning machine, graphite electrode drying machine, etc.
2 The peripheral equipment of the production line includes pure water station, air compressor, negative pressure station, acid mist treatment tower, silane combustion tower, purification and fresh air system, cooling water station, nitrogen tank, oxygen tank, acid and alkali and waste water treatment facilities, special gas (silane, ammonia and carbon tetrafluoride) and independent ground line, etc.
3 The main auxiliary facilities are quartz tube cleaning machine, shaking dryer, metallographic microscope, insertion table, film box, electronic scale, trolley, three-tube diffusion furnace, purification loading table, trolley, purification cabinet, source bottle cabinet, four probes, operation table, hot and cold probes, test table, purification loading table, film pick-up table, electrode storage cabinet, trolley, stencil, slurry mixer, slurry rolling machine, storage cabinet, waste film box, workbench, manual sorting table, packaging mesh belt furnace, trolley, visual cabinet, gas mask, mask cartridge, debris box, hand hydraulic cart, other auxiliary tools, etc.
4 General requirements of the plant (take 25MV solar cell production line as an example).
a. The effective height of the plant is not less than 3.5m, the ground load-bearing is not less than 2500kg/m2, the total area is about 2000m2 (excluding peripheral equipment), of which the purification plant is about 1800m2
b. The ground of the plant is painted with epoxy resin (light green or light gray) with a thickness of not less than 2mm.
c. The cleanliness of the diffusion room of the plant is 10000 level, the rest is 100000 level, the relative humidity is less than 60%, and the ambient temperature is 18~25℃.
d. With independent ground interface, the plant layout meets the fire protection requirements, and the first and second cleaning rooms have emergency showering devices.
e. Reasonable arrangement of sockets in each room, including primary cleaning, diffusion, secondary cleaning, plasma etching, PECVD room: 10A, 220V without grounding 2, 10A, 220V with grounding 2, 20A three-phase four-wire power sockets 2; screen printing, sintering and sorting function hall: 10A, 220V without grounding 6, 10A, 220V with grounding 6, 20A three-phase four-wire power sockets 20A three-phase four-wire power sockets 6.
Crystalline silicon solar cell production line equipment
(1) N-type polysilicon as solar cell wafers
In theory, both boron-doped P-type silicon and phosphorus-doped N-type silicon can be used as raw materials for solar cells, but nowadays, most industries use P-type silicon wafers to produce solar cells because the process is relatively simple and easy to control when using P-type silicon as raw materials for diffusion: while the open-circuit voltage and filling factor of solar cells prepared with N-type silicon are relatively low, and the performance of solar cells produced with N-type silicon as raw materials will gradually degrade as time increases. The advantages of N-type silicon are: compared with P-type silicon, there are more minority carriers at the same resistivity and the conversion efficiency is higher, and N-type silicon has a stronger resistance to pollution.
(2) Use of low-pressure diffusion process
The current industrial production of polycrystalline silicon solar cells in the diffusion process are used in the high temperature, high pressure method, however, the high pressure airflow in the tube is not easy to be controlled, which makes the silicon wafer in the tube can not be uniform diffusion, after into a wafer in different locations on the square resistance differences, that is, the diffusion of phosphorus concentration and junction depth on the surface of the wafer is different, which will cause the reduction of the cell filling factor: and low pressure diffusion process not only can well solve the uneven air flow in the tube to get a more stable square Yang value, but also can reduce the time of the diffusion process and reduce the energy consumption of diffusion, which can play a good role in energy saving in industrial mass production.
(3) Ozone oxidation of silicon wafers
Ozone oxidized silicon wafers are used to enhance the resistance to PID effect. Potential Induced Degrada tion (PID) refers to the phenomenon of power degradation of solar cell modules when subjected to a certain external voltage for a long time, which is a polarization effect. Polycrystalline silicon solar cell modules are grounded with aluminum bezel, and generally the cell modules are connected to form a negative voltage of 1000V, and the cells are subjected to negative voltage which can easily trigger the PID effect. It was found that sodium ions exist in the PV glass of PV modules, and when the modules are subjected to negative voltage, the sodium ions migrate from the glass to the silicon nitride film, thus triggering the PID effect. Under high temperature and humidity, the PID effect is more obvious, so the anti-PID effect becomes one of the important factors to improve the module life.
Research shows that a high refractive index has a better anti-PID effect. The double-layer silicon nitride film in the PECVD process already plays a good role, but in order to make the anti-PID effect more stable, a layer of silicon oxide film can be added on the front side of the wafer before coating, because the silicon chloride film is more chemically stable, has good denseness, and has a certain barrier effect on metal ions. Therefore, it has the effect of enhancing the resistance to PID. Ozone can oxidize silicon wafers at room temperature, so the use of ozone seal process can be done at low energy consumption and the process is relatively simple: rest oxygen can be prepared with hydrogen through the rest oxygen generator equipment, so the raw material is relatively easy to prepare.
(4) Buried grid cell
Buried grid cell is a technology to engrave a slot in a crystalline silicon solar cell by laser and bury the electrode below the surface of the silicon wafer. Due to the good contact of the metal grid line in the silicon wafer, the contact resistance with the heavily doped silicon in the slot is smaller, so the filling factor of the silicon wafer is higher; because the cell grid line is buried in the silicon, it increases the light receiving area of the cell, which not only improves the conversion efficiency of the cell, but also improves the short circuit current.
Of course, there are other technologies as well. With the application of these new technologies, the conversion efficiency of solar cells has been has been greatly improved.