Jul 10, 2021 Solar panels

Do you know the working principle and production process of solar panels?

Understand the role of solar panels in photovoltaic power generation systems and different application areas

Solar panels are the core component of photovoltaic power generation systems. Whether it is an independent photovoltaic power generation system or a grid-connected photovoltaic power generation system, solar panels must provide electrical energy, as shown in Figure 1 and Figure 2.
Different types of solar panels have different applications. Epoxy resin sealed polysilicon solar cell solar panels have low power, usually only a few watts. In addition, epoxy resin has poor environmental weather resistance, so it is mainly used for solar lawn lights, gift toys, etc. The power of laminated encapsulated solar panels is mostly around 240W, and the environmental weather resistance of EVA is better, so laminated solar panels are mostly used in large-scale ground photovoltaic power stations. Vacuum glass encapsulated solar panels or amorphous silicon thin-film solar cell solar panels have a certain degree of light transmission, and are mostly used in the curtain walls, doors and windows of photovoltaic buildings (photovoltaic buildings-integrated, BIPV).

Figure 1 Independent photovoltaic power generation system
Figure 2 Grid-connected photovoltaic power generation system

Knowledge about solar panels
Solar panels are a combination of solar cells, so it is necessary to have a clear understanding of the production process and working principles of solar cells.
①The working principle of solar cells
As mentioned earlier, a solar panel is a combination of solar cells. What is a solar cell? A solar cell is a semiconductor device that converts light energy into electrical energy. Its working principle is based on the photovoltaic effect of the semiconductor PN junction.
Conductive carriers in semiconductors are electrons or holes, and related concepts can be found in any textbook on semiconductor physics. In a pure silicon semiconductor crystal, the number of free electrons and holes are equal. If the silicon crystal is doped with impurity elements such as boron, aluminum, gallium, or indium that can capture electrons, it constitutes a P-type semiconductor; if the silicon crystal is doped with impurity elements such as phosphorus, arsenic, or antimony that can release electrons, it will It constitutes an N-type semiconductor. If these two semiconductors are combined together, electrons or holes will move from the high-concentration area to the low-concentration area, thereby forming a PN junction at the interface and forming a barrier electric field on both sides of the junction, making the electrons Or the diffusion movement of the holes reaches a state of equilibrium. When sunlight irradiates the PN junction, the atoms in the semiconductor release electrons due to light energy, generating electron-hole pairs. Under the action of the barrier electric field, the electrons are driven to the N-type region, and the holes are driven to the P In this way, a photo-generated electric field opposite to the direction of the barrier electric field is formed near the PN junction. A part of the photo-generated electric field cancels the barrier electric field, and the rest makes the thin layer between the N-type region and the P-type region generate electromotive force, that is, photovoltaic electromotive force. When the external circuit is connected, electrical energy is output. This is the basic principle of PN junction contact monocrystalline silicon solar cell power generation. If dozens or hundreds of solar battery cells are connected in series and parallel to form a solar cell solar panel, under the sunlight, a considerable output power can be obtained.
The relevant schematic diagrams are shown in Figure 5 to Figure 8.

Figure 5 Physical image formed by PN junction
Figure 6 Energy band diagram of a semiconductor
Figure 7 Band diagram of PN junction in open circuit
Figure 8 Energy band diagram of PN junction in the case of short circuit

②The production process of crystalline silicon solar cells
The preparation method of crystalline silicon solar cell includes the following steps: texturing-diffusion-edge cutting-impurity removal glass layer-plating anti-reflective film-partial removal of anti-reflective film-cleaning-printing-sintering, then the crystalline silicon can be obtained Solar cells, in order to better understand the entire production process of solar cells, here is an example of crystalline silicon solar cells, as shown in Figure 3.

Figure 3 Manufacturing and inspection process of crystalline silicon solar cells

③The production process of thin-film solar cells
For thin film solar cells, the production process is very different from crystalline silicon solar cells. People usually use various thin film deposition techniques to prepare solar cells, such as PECVD (plasma enhanced chemical vapor deposition), RTCVD (rapid thermal chemical vapor deposition) ), magnetron sputtering, thermal evaporation, etc. Figure 4 shows the production flow chart of GIGS thin-film solar cells. The thin-film deposition uses co-evaporation technology, the substrate is glass, and the sputtering deposition of electrode materials and laser grooves are used to achieve contact, interconnection and integration.

Figure 4 GIGS thin film solar cell production process