Photovoltaic (PV) systems directly convert sunlight into electricity. The PV effect is the process from which light (photons) is converted into electric current. Different PV technologies have different efficiencies. There are 3 main classes of photovoltaic semiconductor technologies:
- Crystalline silicon cells —Crystalline Silicon semiconductors dominate the world PV market, accounting for nearly 90 percent in 2013. Although single crystalline cells account for the majority of PV panels, there are a few types of silicon PV technologies on the market today — single crystalline silicon (c-Si), multicrystalline (mc-Si), and silicon heterostructures.
- Thin film technologies — Thin film technologies are characterized by one or more thin layers of photovoltaic material (at least 10 times thinner than crystalline silicon technologies) deposited onto glass, plastic, metal, or other surface. As a result, thin film cells are more flexible and weigh less. They can be integrated into buildings, including as photovoltaic material laminated onto windows. Thin film solar panels within panes of glass are used in some of the largest PV power plants. Some thin film cell technologies include:
- amorphous silicon (a-Si) and other thin film (TF-Si)
- cadmium telluride (CdTe);
- copper indium gallium deselenide (CIS or CIGS);
- dye-sensitized solar cells (DSC); and
- single crystalline gallium arsenide (GaAs)
- Multijunction cells— Multijunction cells utilize light at different wavelengths more efficiently than crystalline silicon cells through multiple stacked layers of semiconductors. Although more efficient at converting sunlight into electricity, they are currently less efficient economically due to their complexity and resulting manufacturing costs. This price premium has limited their application mainly to the aerospace industry, which is uniquely willing to pay more for their higher efficiencies.