The photovoltaic cell plate is a photoelectric conversion element made of a semiconductor material. At present, there are many materials and methods for making photovoltaic cells, and the work efficiency is also different. According to different semiconductor materials, photovoltaic cells can be divided into selenium photovoltaic cells, gallium arsenide photovoltaic cells, silicon photovoltaic cells, and so on. At present, the most widely used and promising development is silicon photovoltaic cells. Silicon photovoltaic cells are cheap, high conversion efficiency, long life, and suitable for receiving infrared light. Selenium photocells have low photoelectric conversion efficiency and short life span, are suitable for receiving visible light, and are most suitable for manufacturing illuminance meters. The conversion efficiency of gallium arsenide photovoltaic cells is slightly higher than that of silicon photovoltaic cells, the spectral response characteristics are most consistent with the solar spectrum, and the operating temperature is the highest, and it is more resistant to cosmic ray radiation. Therefore, its application in power sources such as cosmic spacecraft, satellites, and space probes is promising.
At present, there are three kinds of silicon photovoltaic cells that have been commercialized in the world: monocrystalline silicon photovoltaic cells, polycrystalline silicon photovoltaic cells and amorphous silicon photovoltaic cells. The single crystal silicon photovoltaic cell has the same quality as the single crystal silicon material used in the semiconductor industry, which makes the cost of the material relatively expensive. Monocrystalline silicon photovoltaic cells have the highest manufacturing cost, but they also have the highest photoelectric conversion efficiency. The irregularity of the crystal orientation of polycrystalline silicon photovoltaic cells means that the positive and negative charge pairs cannot be completely separated by the PN junction electric field. Because the charge on the boundary between the crystal and the crystal may be lost due to the irregularity of the crystal, the efficiency of polycrystalline silicon photovoltaic cells is slightly lower than that of ordinary single crystal silicon. However, polycrystalline silicon photovoltaic cells can be produced by casting, so its cost is lower than that of monocrystalline silicon photovoltaic cells. Amorphous silicon photovoltaic cells are thin-film batteries with low cost, but their photoelectric conversion efficiency is relatively low, and they decay under light. Currently, they are mostly used for low-light power sources, such as watches and calculators.
The spectral characteristics of photovoltaic cells are determined by the material. The selenium photovoltaic cell has a high sensitivity in the visible spectrum, and the peak wavelength is around 540nm, which is suitable for measuring visible light. The application range of silicon photovoltaic cells is 400~1100nm, and the peak wavelength is around 850nm, so silicon photovoltaic cells can be used in a wide range.
Crystalline silicon photovoltaic cells are expensive to make and are the most important part of the cost of photovoltaic systems. In the international market, the current price of photovoltaic cells is about US$3.15/W. A 1m² photovoltaic cell can only receive 1㎡ of sunlight, and the average photoelectric conversion efficiency is about 15%, because this photovoltaic power generation method is always restricted by the price of 1:1 wafers. The incident angle of the sun’s rays will change with time, and this cosine effect also reduces the photoelectric conversion efficiency. For a long time, these limiting factors have made the cost of photovoltaic cell power generation 2 to 3 yuan/kWh. In fact, the cost of existing photovoltaic cells is about 5 to 8 times the cost of coal power.