A semiconductor is a substance with an electrical conductivity between that of a conductor and an insulator — the conductivity of a semiconductor increases as temperature increases. Adding appropriate impurities also increases conductivity.
An amorphous semiconductor also called “thin film” is a non-crystalline semiconductor material that has no long-range order. Although easier and cheaper to make than a crystalline semiconductor, it is less efficient and slowly degrades over time.
A layer of an amorphous semiconductor, such as copper indium diselenide, cadmium telluride, gallium arsenide, or amorphous silicon, a few microns or less in thickness, is used to make solar cells.