1. Amorphous silicon (a-Si) is the non-crystalline form of silicon used for solar cells and thin-film transistors in LCD displays.
2. Amorphous silicon (a-Si), silicon in which some atoms in the structure remain unbonded, lacks long-range order, but can be produced, in principle, even more cheaply than multicrystalline silicon.
https://en.wikipedia.org/wiki/Amorphous_silicon (1.); http://pvcdrom.pveducation.org/MANUFACT/A-SI.HTM (2.)