Thin film photovoltaic cells use layers of semiconductor materials only a few micrometers thick, attached to an inexpensive backing such as glass, flexible plastic, or stainless steel. Semiconductor materials for use in thin films include amorphous silicon (a-Si), copper indium diselenide (CIS), and cadmium telluride (CdTe). Amorphous silicon has no crystal structure and is gradually degraded by exposure to light through the Staebler-Wronski Effect. Hydrogen passivation can reduce this effect. Because the quantity of semiconductor material required for thin films is far smaller than for traditional PV cells, the cost of thin film manufacturing is far less than for crystalline silicon solar cells.
Group III-V Technologies
These photovoltaic technologies, based on Group III and V elements in the Periodic Table, show very high conversion efficiencies under either normal sunlight or sunlight that is concentrated (see “Concentrating Collectors” below). Single-crystal cells of this type are usually made of gallium arsenide (GaAs). Gallium arsenide can be alloyed with elements such as indium, phosphorus, and aluminum to create semiconductors that respond to different energies of sunlight.