α-Si, also known as noncrystalline silicon, is a from of monatomic silicon. It is a brown-black or dark-grey micro crystal. Compare with crystalline silicon, amorphous silicon is a material which has more active chemical properties. At heating condition, use silicon tetraauragen to interact with active metal (such as sodium, potassium, etc), or use reducing agents such as carbon to interact with silicon dioxide, it can be obtained. This kind of α-Si, its structural characteristic is a lack of long-range order. In addition, the presence of the large number of dangling bonds cause a high defect density and the pure α-Si is not very useful. Use the Glow Discharge Vapor Deposition method to produce hydrogenated amorphous silicon films, in which hydrogen compensates the so-called “dangling” bonds, and dope it and create a pn junction. Around the solar radiation peak, the absorption coefficient of a-Si is much higher than that of crystalline silicon, about one magnitude higher. The band gap ranges from 1.7 eV to 1.8 eV, and its mobility and minority carrier lifetime is far lower than that of the crystalline silicon.