Polycrystalline silicon, also known as polysilicon or poly-Si, is a type of silicon crystal made up of many small silicon crystals. It is used in the manufacture of semiconductor devices such as transistors, solar cells, and integrated circuits. Polycrystalline silicon is produced by melting and recrystallizing high-purity silicon. It is a key material in the production of microelectronic devices and is used in a variety of applications, including photovoltaics, electronics, and optoelectronics.