Solar Photovoltaic Cell Basics
When light shines on a photovoltaic (PV) cell, it may be reflected, absorbed, or pass right through it. The PV cell is composed of semiconductor material, which combines some properties of metals and some properties of insulators. That makes it uniquely capable of converting light into electricity. When light is absorbed by a semiconductor, photons of light can transfer their energy to electrons, allowing the electrons to flow through the material as electrical current. This current flows out of the semiconductor to metal contacts and then makes its way out to power your home and the rest of the electric grid.
There are a variety of different semiconductor materials used in solar cells. Learn more below about the most commonly-used materials.
Silicon is, by far, the most common material used in solar cells, representing approximately 90% of the modules sold today. It is also the second most abundant material on Earth (after oxygen) and the most common semiconductor used in computer chips. Crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice. This lattice provides an organized structure that makes conversion of light into electricity more efficient.
Solar cells made out of silicon currently provide a combination of high efficiency, low cost, and long lifetime. Modules are expected to last for 25 years or more, still producing more than 80% of their original power after this time.
A thin-film solar cell is made by depositing one or more thin layers of PV material on a supporting material such as glass, plastic, or metal. There are two main types of thin-film PV semiconductors on the market today: cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). Both materials can be deposited directly onto either the front or back of the module surface.
CdTe is the second-most common PV material after silicon and enables low-cost manufacturing processes. While this makes them a cost-effective alternative, their efficiencies still aren’t quite as high. CIGS cells have favorable electronic and optical properties, though the complexity involved in combining four elements makes the transition from lab to manufacturing or challenging. Both CdTe and CIGS require more protection than silicon to enable long-lasting operation outdoors.
Organic PV, or OPV, cells are composed of carbon-rich polymers and can be tailored to enhance a specific function of the cell, such as sensitivity to a certain type of light. This technology has the theoretical potential to provide electricity at a lower cost than silicon or thin-film technologies. OPV cells are only about half as efficient as crystalline silicon and have shorter operating lifetimes, but could be less expensive to manufacture in high volumes. They can also be applied to a variety of supporting materials, making OPV able to serve a wide variety of uses.
Concentration PV, also known as CPV, focuses sunlight onto a solar cell by using a mirror or lens. By focusing sunlight onto a small area, less PV material is required. PV materials become more efficient at energy conversion as the light becomes more concentrated, so the highest overall efficiencies are obtained with CPV cells and modules. However, more expensive materials, manufacturing techniques, and tracking are required, so demonstrating the necessary cost advantage over today’s high-volume silicon modules has become challenging.
SOLAR CELL PERFORMANCE AND EFFICIENCY
The efficiency of a cell is simply the amount of electrical power coming out of a cell divided by the energy from sunlight coming in. The amount of electricity produced from PV cells depends on the quality (intensity and wavelengths) of the light available and multiple performance characteristics of the cell. Learn more about conversion efficiency.