Single crystal silicon has two isomorphous, crystalline and amorphous forms. Crystalline silicon is further divided into single crystal silicon and polycrystalline silicon, both of which have a diamond lattice. The crystal is hard and brittle, has a metallic luster, and is electrically conductive, but less electrically conductive than metal, and increases with temperature and has semiconducting properties.
Monocrystalline silicon is an indispensable basic material in modern science and technology, such as electronic computers and automatic control systems in daily life. Televisions, computers, refrigerators, telephones, watches and cars are all inseparable from monocrystalline silicon materials. As one of the popular materials for technical applications, monocrystalline silicon has penetrated into every corner of people’s lives.
Polycrystalline silicon polysilicon is a form of elemental silicon. When the molten elemental silicon is cured under supercooled conditions, the silicon atoms are arranged in a diamond lattice form into a plurality of crystal nuclei. If the crystal nucleus grows into crystal grains having different crystal orientations, the crystal grains combine and crystallize into polycrystalline silicon.
Polycrystalline silicon can be used as a raw material for drawing single crystal silicon, and the difference between polycrystalline silicon and single crystal silicon is mainly manifested in physical properties.
For example, in terms of mechanical properties, optical properties and thermal properties anisotropy, it is less noticeable than single crystal silicon; in terms of electrical properties, polycrystalline silicon crystals have much lower conductivity than single crystal silicon, and even electrical conductivity is very high. difference.
In terms of chemical activity, the difference between the two is very small. Polycrystalline silicon and single crystal silicon can be distinguished from each other in appearance, but true identification must be determined by analyzing the crystal plane orientation, conductivity type, and resistivity.
Monocrystalline silicon cells have high cell conversion efficiency and good stability, but are costly. As early as 20 years ago, monocrystalline silicon cells broke through the technical barrier of more than 20% photoelectric conversion efficiency.
The cost of polycrystalline silicon cells is low and the conversion efficiency is slightly lower than that of Czochralski silicon solar cells. Various defects in the material, such as grain boundaries, dislocations, micro-defects and impurities in the material, such as carbon and oxygen, and contamination in the process. Transition metals are considered to be the gateway for polycrystalline silicon cells with a photoelectric conversion rate of no more than 20%. Researchers at the Fraunhofer Institute in Germany have adopted this new technology and are the first in the world to achieve a photoelectric conversion rate of 20.3% for polycrystalline silicon solar cells.