Amorphous silicon solar cells were first introduced commercially by Sanyo in 1980 for use in solar-powered calculators, and shipments increased rapidly to 3.5 MWp by 1985 (representing about 19% of the total PV market that year). Shipments of a-Si PV modules reached ~40 MWp in 2001, but this represented only about 11% of the total PV market.
The efficiency of amorphous silicon solar cells has a theoretical limit of about 15% and realized efficiencies are now up around 6 or 7%. If efficiencies of 10% can be reached on large area thin film amorphous silicon cells on inexpensive substrates, then this would be the best approach to produce low cost electricity.
Amorphous silicon solar cells are commercially available and can be produced on a variety of substrates ranging from glass to flexible thin foils. Cells are built in p-i-n or n-i-p configurations, where p and n represent thin doped (amorphous or nanocrystalline) layers, and the absorber layer is an intrinsic undoped layer.
US Department of EnergylO it is essential to develop thin film solar cells with efficiencies of at least 8%, and amorphous silicon, based as it is on an accepted semiconductor, is there fore very attractive.
WHY AMORPHOUS SILICON? The first reports of amorphous silicon photovoltaic diodes appeared in 19761 , and si~c3 ShSn several other device applica tions have been suggested ' , , , but it is the promise of cheap solar cells with efficiencies greater than the present 5-6% which excites most attention.
The manufacture of amorphous silicon photovoltaic cells is based on plasma-enhanced chemical vapor deposition (PECVD), which can be used to produce silicon thin film. Substrate can be made of the flexible and inexpensive material in larger sizes, for example stainless steel or plastic materials. The process is the roll-to-roll method.