Photovoltaic Cell

The least expensive type of solar cell is made of a disordered type of silicon mixed with hydrogen. This hydrogenated amorphous silicon is used in photovoltaic cells for calculators and wristwatches. Amorphous silicon is deposited on a substrate as a coating.

In 1974, David Carlson at RCA's David Sarnoff Laboratory first made an amorphous silicon photovoltaic cell. By 1988, amorphous cells with about 13% efficiency were made using a stacked-junction PIN device.

Because large areas can be coated, the cost-per-device is relatively low. Its bandgap is 1.7 eV, which means that it absorbs light at shorter wavelengths than the crystalline silicon and that it works well under fluorescent lights. Because it absorbs light efficiently, the cells can be made very thin, which uses less material and also helps make the cells less expensive. These devices, however, degrade in direct sunlight and have a shorter lifetime than crystalline cells.