Photovoltaic, Thin Film, Silicon
Amorphous silicon is less expensive to produce than either mono or poly-crystalline silicon. It is non-crystalline, meaning that the atomic structure is more randomized. While it operates at a lower efficiency than crystalline structures (about half the efficiency of monocrystalline Si), it can be placed in much thinner applications which can lead to a lower cost per watt capacity of the solar cell design. Its conversion efficiency is around 12%.
Other types of thin film silicon are Protocrystalline and Nanocrystalline (aka Microcrystalline). Some variations that combine layers of different types of thin film silicon have been referred to as Micromorph (a combination of the terms MICROcrystalline and aMORPHous).