Currently, more than 90% of photovoltaic cells each year are silicon photovoltaic cells, therefore, silicon is the most commonly used semiconductor for the production of photovoltaic cells.
Silicon is a chemical element, the chemical symbol is Si, the atomic number is 14, and the relative atomic mass is 28.0855. Silicon is a kind of semiconductor, it has two kinds of amorphous and crystalline, it belongs to the IVA group on the periodic table, that is, the carbon group element. The English name of silicon is silicon, which comes from the Latin silex, sili-cis, which means flint (flint).
Silicon has good high temperature resistance, radiation resistance and high reliability, so it is especially suitable for making high-power devices. At present, not only most photovoltaic cells are made of silicon material, but most of integrated circuit semiconductor devices are also made of silicon material. Silicon is the easiest semiconductor material to manufacture, and among the semiconductor materials, single crystal silicon has the largest diameter. At present, the production of single crystal silicon rods with a diameter of 12in ● is a mature technology, and the production of 18in single crystal silicon rods is no longer a problem. The maximum diameter of arsenide single crystal is only 6in.
Silicon crystals have the best integrity. In ingot semiconductor materials, single crystal silicon has the best crystal integrity, and it is now possible to produce dislocation-free single crystals. So far, there have been no successful examples of growing dislocation-free single crystals from other semiconductor materials. Among semiconductor materials, silicon semiconductor materials have the lowest production cost.
Due to the unique properties of silicon material, it has become the foundation of modern electronic industry and information society. Its development is a milestone in the field of materials and electronics in the 20th century. Its development and application directly promoted the rapid development of global technology and industry in the 20th century. , the development of human beings is said to have entered the “Silicon Age”.
Silicon is rich in resources and widely distributed in nature. It is the main element that constitutes minerals and rocks. It is one of the most abundant elements in the earth’s crust, second only to oxygen. Its abundance in the earth’s crust is about 27.72%. But most of them exist in the form of compounds, of which the most exist in the form of silica and silicate, and natural elemental silicon has never been found. The main components of the rocks in the mountains, the sand and gravel on the beach, the bricks and tiles of the houses, the floors of the buildings, the glass of the windows, etc. are all silicon, and even our bodies contain trace amounts of silicon.
Silicon used in industry is usually obtained by reducing silica with carbon in an electric furnace. Silicon is silver-gray, with metallic luster, brittle and brittle, not easy to purify, and has semiconductor properties. The melting point of silicon is 1420°C; the boiling point is 2600°C. Usually silicon participates in the reaction in a tetravalent state and is in an anionic state in the compound. Silicon behaves much like carbon in many compounds. Silicon is easy to combine with halogen to form SiX4 type compound, which reacts with oxygen at red-hot temperature, reacts with sulfur at 600℃, and reacts with nitrogen at 1000℃. Silicon is easily dissolved in molten magnesium (Mg), copper (Cu), iron (Fe) and nickel (Ni) to form silicides. Silicon is soluble in liquid or gaseous hydrofluoric acid (HF) and in aqua regia (HNO3:HC1=1:3), but does not react with any concentration of sulfuric acid, nitric acid and hydrochloric acid. In the red-hot state, silicon slowly interacts with water vapor and releases hydrogen (H2).
Silicon material has special physical and chemical properties and good semiconductor properties. Silicon shrinks in volume when it melts and increases in volume when it solidifies, which is basically the same property as water. Silicon has high hardness, high brittleness, and good semiconductor properties. Its intrinsic carrier concentration is 1.5×1010/cm3, its intrinsic resistivity is 1.5×1010☊∙cm, and its electron mobility is 1350cm2/(V ∙s), and the hole mobility is 480 cm2/(V∙s).
The forbidden bandwidth of silicon (1.1eV), the leakage current is small. Solid-state electronics began to appear with the invention of the bipolar transistor in 1947. The semiconductor material used to make diodes and triodes at the beginning was germanium (Ge). However, due to the narrow band gap (0.66eV) of germanium, there is a considerable leakage current in the reverse phase of the PN junction. This limits germanium devices to work only below 100°C. In addition, integrated circuit planarization requires the ability to create a passivation layer on the semiconductor surface. Germanium oxide can be used as a passivation layer, but it is difficult to form, and it is soluble in water and decomposes at 800 °C. These limitations dwarf that of silicon as a material for making integrated circuits. Silicon has a wider band gap (1.1eV) and less leakage current, so silicon devices with a maximum operating temperature of around 150°C can be produced. In addition, silicon oxide SiO2 is easy to generate, and its chemical properties are very stable.
Read more: What are the main materials used to produce photovoltaic cells?