What is the manufacturing process of solar cell?
After silicon wafers are produced through the cutting of silicon wafer, they cannot be directly combined to form solar cells. Several technological processes must be passed to produce photovoltaic cells. The manufacturing process of the solar cell is as follows.
(1) Choice of silicon wafer
The choice of silicon wafer is to select silicon wafers with consistent performance. If silicon wafer cells with inconsistent performance are combined to form a single solar cell, the output power will be reduced.
(2) Cleaning of silicon wafer
The cleaning of silicon wafers is to use high-purity water or organic solvents (such as trichloroethylene, acetone, toluene, etc.) to remove the contaminated dust, metal chips, grease, etc. on the silicon wafers.
(3) Surface corrosion of silicidation
In order to make the surface of the silicon wafer bright and flat, the damage layer caused by mechanical cutting must be removed. Commonly used corrosion methods are alkaline corrosion and acid corrosion. Alkaline corrosion is to use alkaline solutions such as sodium hydroxide and potassium hydroxide for corrosion. The biggest advantage of the finished product made by alkaline corrosion is that the performance of the battery is almost the same. Acidic corrosion is to use a mixture of nitric acid and hydrofluoric acid (the ratio is 10:1 to 2:1) for corrosion. The surface of the silicon wafer that has been etched by acid is smooth and bright. Different ratios can be used to control the corrosion rate.
(4) Diffusion production
The key reason why solar cells can emit electricity under the action of sunlight is that there are PN junctions in the solar cells. Therefore, the production of PN junction is the most important process in the production of solar cells. At present, the method suitable for industrial production is to first heat the boron chloride sheet and ventilate oxygen, and the surface will generate diboron trichloride, and then make it chemically react with the silicon crystal, so that the formed borosilicate glass will be deposited on the silicon crystal. surface. Then use nitrogen as a protective atmosphere to diffuse boron nitride under high temperature conditions to form a PN junction.
(5) To remove the back junction
To remove the back junction is to remove the PN junction formed on the surface of the silicon wafer. Commonly used methods include grinding wafer method, chemical etching method, steaming aluminum or screen printing aluminum paste sintering method. The polishing method is to use emery to polish the back side. The chemical etching method uses an etchant to remove the back junction, and at the same time, the diffusion layer around the silicon wafer is also etched away. The sintering method of vaporized aluminum or wire-brushed aluminum paste is to vacuum vaporize or wire-brush a layer of aluminum on the back of the diffused silicon wafer, and heat the silicon wafer to form an aluminum-silicon alloy layer. This process is actually a doping process of silicon crystals.
(6) Making positive and negative electrodes
The conductive material that forms close contact with the PN junction of the battery is called an electrode. In order to convert the energy obtained from the sun into the required energy, positive and negative electrodes must be made on the battery. The electrode made on the light side of the battery is called the upper electrode, and the electrode made on the back of the battery is called the lower electrode or the back electrode. The upper electrode is generally shaped to facilitate light collection. In order to reduce the resistance when the battery is connected in series, the lower electrode should be distributed on the back of the battery. And most or all of the back of the battery should be covered by the lower electrode, which is like the dry battery in a flashlight. Above the dry battery is a copper cap, and under the copper cap is a carbon rod (upper electrode) with a large amount of negative charge. The whole shell (material zinc) is covered by the lower electrode (negative electrode).
Electrodes are made by vacuum evaporation method, chemical evaporation nickel method, silver (aluminum) paste printing and sintering method, etc. The main process of the aluminum paste printing and sintering method is: placing the silicon wafer in a vacuum machine capable of vapor deposition, a layer of aluminum film will condense on the silicon wafer, which can be vaporized into a layer of aluminum under the action of high temperature, and then needle welding A layer of solder composed of tin, aluminum, and silver alloys. This method is the main method for commercial production of solar silicon cells.
(7) Corrosion surrounding
The diffusion layer around the silicon wafer will short-circuit the upper and lower electrodes, so it must be removed. Generally, the silicon wafer is corroded in an etching solution composed of nitric acid and hydrofluoric acid
(8) Evaporated film
This method is to vapor-deposit one or more layers of silicon dioxide film on the front of the battery, which not only protects the battery, but also has the effect of reducing light reflection. With this layer of film, the incident light can be reduced to about 10%. If some corrosive agents are used to treat the velvet surface of the silicon battery, as shown in Figure, it can be seen that the surface of the battery is corroded to form a velvet surface like a continuous mountain range, so that the surface of the silicon battery can not only Receiving the energy of the incident light, it can also receive the energy of refraction.
(9) Inspection and testing
After testing the open-circuit voltage, short-circuit current, maximum output power and other values of the battery, it is easy to know the quality of the solar cell.
The above is the specific manufacturing process of solar cell.
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