Classification and manufacturing process of solar cells

Classification of solar cells

Solar cells are mainly divided into crystalline silicon solar cells and thin-film solar cells. Crystalline silicon solar cells are further divided into monocrystalline silicon solar cells and polycrystalline silicon solar cells. There are many types of thin-film solar cells, mainly amorphous silicon solar cells.

The monocrystalline silicon solar cell material has complete crystallization and high conversion efficiency, about 14% to 17%, up to 24%, the color is mostly black, and the four corners are arc-shaped. Its production technology is mature, and it is widely used in aerospace and high-tech products. However, the manufacturing process of monocrystalline silicon solar cells is complicated, the manufacturing energy consumption is high, and the cost is high.

Compared with monocrystalline silicon solar cells, polycrystalline silicon solar cells have lower cost and shorter production time, and have an important position in the market. It is a collection of many single crystal particles, the conversion efficiency is about 13% to 15%, up to 20%, the color is mostly blue, and the surface shows a pattern.

Classification and manufacturing process of solar cells
Figure 1 – Solar cell

Amorphous silicon solar cells are made of amorphous silicon materials and are basically made into thin-film batteries (about 1mm thick). The silicon material consumes very little, and it can be directly deposited on a large area of glass, stainless steel, plastic plates and other materials. The manufacturing process and equipment are simple, the manufacturing time is short, and the energy consumption is low, which is suitable for mass production. Its conversion efficiency is about 5%~8%, up to 13%, and it can generate electricity even under low light. Its main disadvantage is that the stability is slightly poor, but the price is low and the low-light performance is good, and it is widely used in civilian products. In addition, because the thin film battery is flexible, in addition to being made into a plane, it can be made into a non-planar structure, which can be combined with a building or become a part of a building, and it is widely used.

Solar cell manufacturing process

Generally, the size of a single solar cell mainly has two specifications: 156mm×156mm and 125mm×125mm, and the working voltage is about 0.48~0.5V. Because the voltage, current and power of the cells are very small, it is necessary to connect several solar cell cells in series to reach the available voltage, and then output large current in parallel to achieve a larger power output. A large-area solar cell module, also known as a solar cell panel, can be formed by encapsulating and protecting multiple cells in series and parallel. Solar cell module is the basic unit of solar power generation system.

Figure 2 shows a schematic diagram of battery slices in series. The upper electrode wire (negative electrode) of one battery piece and the lower electrode wire (positive electrode) of the next battery piece can be welded together through the bus belt, and then multiple battery pieces can be connected in series to form a battery string, and then lead out the welding leads of the positive and negative poles of the entire battery string. Generally, a solar cell module is composed of 36, 72, 54, 60, etc. in series, regardless of the power. The common arrangement methods are 4×9 slices, 6×6 slices, 6×12 slices, 6×9 slices, 6×10 slices and so on. Taking 36 pieces in series as an example, the working voltage is about 17~17.5V. The battery string is then packaged. Different types of solar cell modules have different packaging processes. Here we introduce the common packaging methods for ordinary silicon solar cells. First, use tempered glass (also called white glass) to encapsulate the battery string. Tempered glass has high strength and good light transmittance, which can effectively protect the cells; the bottom of the cell is made of thermoplastic polyvinyl chloride composite film (TPT) as the back, which has good insulation properties and can resist ultraviolet rays and environmental corrosion. The three are bonded by hot-melt adhesive film (EVA). EVA has good adhesion after melting and solidification under hot pressure, and has high light transmittance, flexibility, impact resistance and corrosion resistance. The encapsulation level is shown in Figure 3.

Classification and manufacturing process of solar cells
Figure 2 – Schematic diagram of cell series connection
Classification and manufacturing process of solar cells
Figure 3- Solar cell encapsulation

Lay the above materials in layers and put them into the laminator, draw out the air and heat to melt and bond the EVA, and finally cool and take out the modules, install the aluminum frame and seal them, so as to increase the strength of the modules and prolong the service life of the battery. A junction box is glued to the lead on the back of the battery assembly to facilitate the connection between the battery and other devices or batteries.

Figure 4 shows the front and back sides of the packaged monocrystalline silicon and polycrystalline silicon solar cell modules. The battery junction box can be seen on the reverse side.

Classification and manufacturing process of solar cells
Figure 4 – The front and back of monocrystalline silicon and polycrystalline silicon solar cell modules

At present, there are many types of solar panels, generally 1.5m long and 0.8m wide. The large ones can be up to 2m long and 1m wide, and can also be made into different sizes, different voltages, and different shapes according to needs, as shown in Figure 5.

Classification and manufacturing process of solar cells
Figure 5 – Various sizes of solar cell modules