Solar cell is a device that uses the photoelectric conversion principle to convert the solar radiation into electric energy through semiconductor materials. This photoelectric conversion process is usually called “photovoltaic effect”. Therefore, solar cell is also called “photovoltaic cell”. The semiconductor material used for solar cell is a special material between conductor and insulator.

In order to reduce the manufacturing cost of solar cells, scientists follow two paths: one is to develop novel solar cell materials, and the other is to improve the conversion efficiency of solar cells. To convert the inexhaustible sunlight into electric energy for the benefit of mankind, the core technology is the photoelectric conversion rate of solar cells.

There are more than ten kinds of semiconductor materials known to manufacture solar cells, so there are many kinds of solar cells. At present, silicon solar cells are the most mature solar cells with commercial value and the most widely used in the market.

The manufacturing process flow of silicon solar cell is as follows:

1. Silicon wafer cutting, material preparation:

The monocrystalline silicon material used for industrial production of silicon cells generally adopts the solar grade monocrystalline silicon rod of crucible direct drawing method. The original shape is cylindrical, and then cut into square silicon wafer (or polycrystalline square silicon wafer). The side length of silicon wafer is generally 10 ~ 15cm, the thickness is about 200 ~ 350um, and the resistance is about 1 Ω. Cm.

2. Remove the damaged layer:

There are a lot of surface defects in the cutting process of silicon wafer, which will produce two problems. First, the surface quality is poor, and these surface defects will lead to the increase of debris in the battery manufacturing process. Therefore, alkali or acid corrosion is generally used to remove the cutting damage layer, and the corrosion thickness is about 10um.

3. Cashmere making:

Flocking is to etch the relatively smooth surface of raw material silicon wafer through acid or alkali, make it uneven and rough, form diffuse reflection, and reduce the loss of solar energy directly onto the surface of silicon wafer.

For monocrystalline silicon, the method of NaOH and alcohol is generally used for corrosion. Using the anisotropic corrosion of monocrystalline silicon, countless pyramid structures are formed on the surface. The temperature of alkali solution is about 80 ℃, the concentration is about 1 ~ 2%, and the corrosion time is about 15 minutes. For polycrystals, acid corrosion is generally used.

4. Diffusion bonding:

The purpose of diffusion is to form PN junction. Phosphorus is widely used as n-type doping. Due to the high temperature required for solid-state diffusion, it is very important to clean the silicon wafer surface before diffusion. It is required to clean the silicon wafer after flocking, that is, use acid to neutralize the alkali residue and metal impurities on the silicon wafer surface.

5. Edge etching and cleaning:

In the diffusion process, a diffusion layer is also formed on the peripheral surface of the silicon wafer. The peripheral diffusion layer forms a short circuit ring between the upper and lower electrodes of the battery, which must be removed. Any small local short circuit around the battery will reduce the parallel resistance of the battery and become waste.

At present, plasma dry etching is used in industrial production. Under the condition of glow discharge, fluorine and oxygen alternately act on silicon to remove the periphery containing diffusion layer.

The purpose of post diffusion cleaning is to remove the phosphorus silicon glass formed in the diffusion process.

6. Sedimentary antireflection layer:

The purpose of depositing antireflection layer is to reduce surface reflection and increase refractive index. PECVD deposition of sin is widely used. When PECVD deposition of sin, it not only grows sin as antireflection film, but also generates a large amount of atomic hydrogen. These hydrogen atoms can have the dual effects of surface passivation and bulk passivation on polysilicon wafer, which can be used for mass production.

7. Screen-printed upper and lower electrodes:

The preparation of electrode is a crucial step in the preparation of solar cell. It not only determines the structure of emission region, but also determines the series resistance and the area covered by metal.

Vacuum evaporation or electroless plating technology was first used, but now screen printing is widely used, that is, silver paste aluminum paste (silver aluminum paste) is printed on the front and back of solar cells through special printing machines and templates to form positive and negative electrode leads.

8. Co-firing to form metal contact:

Crystalline silicon solar cells need three times of printing metal slurry. In the traditional process, secondary sintering is required to form good ohmic contact with metal electrodes. In the co sintering process, only one sintering is required to form ohmic contact between upper and lower electrodes at the same time. In the production of screen-printed electrodes for solar cells, chain sintering furnace is usually used for rapid sintering.

9. Solar cell test:

The completed solar cells are classified by test.