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.
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 (a-Si:H) thin films are currently widely used as passivation layers for crystalline silicon solar cells, leading, thus, to heterojunction cells (HJT cells), as described in Chap. 7, next-up. HJT cells work with passivated contacts on both sides.
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.
Hydrogenated amorphous silicon (a-Si:H) based thin film solar cells are designed successfully by using finite-difference time-domain method. Three optical models are developed for comparative studies to optimize the performance of the solar cell.
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.