Grain size and structure engineering during Al-induced crystallization for Si thin-film solar cells

In this study the Al-induced crystallization of a-Si on glass at temperatures below 550 degreesC is studied as an alternative process to solid phase and laser crystallization. The process of an AI and Si layer exchange during isothermal annealing is exploited for the formation of a continuous polycrystalline Si film. This Si layer consists of grains of several pm in diameter and can be formed in less than 1 hour. The temperature as one of the most important parameters is studied to deliberately influence the grain size. It is shown that the lower the temperature the larger is the grain size but the slower is the overall crystallization process. For the use of the poly-Si in subsequent solar cell processing, various structures of the layered Al/Si system after crystallization are discussed. Their different feasibilities for Si thin-film solar cells are compared in terms of layer sequence and surface roughness.