It wasn't until 1974 that researchers began to realize that amorphous silicon could be used in PV devices by properly controlling the conditions under which it was deposited and by carefully modifying its composition. Today, amorphous silicon is commonly used for solar-powered consumer devices that have low power requirements (e.g., wrist watches and calculators).
Amorphous silicon absorbs solar radiation 40 times more efficiently than does single-crystal silicon, so a film only about 1 micron (one one-millionth of a meter) thick can absorb 90% of the usable solar energy. This is one of the most important factors affecting its potential for low cost. Other principal economic advantages are that amorphous silicon can be produced at a lower temperature and can be deposited on low-cost substrates. These characteristics make amorphous silicon the leading thin-film PV material.
The versatility of amorphous silicon is shown in this flexible roof-shingle module developed under a DOE project called Photovoltaics Building Opportunities in the United States (PV:BONUS). The shingle can be built right into new homes where covenants would prohibit more conventional PV modules.