It's a GaAs: Gallium Arsenide Solar Cells

Gallium arsenide (GaAs) solar cells are known for two things: high conversion efficiency and a high price tag. Made from gallium and arsenic, GaAs cells are most famous for their use in outer space and on solar-powered race cars. In the laboratory, GaAs solar cells have reached sunlight conversion efficiencies as high as 29% under concentrated light. In real world conditions, they can average up to 20% efficiency.

According to Sandia National Laboratory, gallium arsenide has several advantages, making it a contender for high-efficiency solar cell production:

• GaAs has a band gap that is virtually ideal for single-junction solar cells.
• Its high absorption rate requires cells of just a few microns thick (compare with 100-micron thickness required for silicon solar cells).
• Insensitive to heat
• Resistant to radiation damage

Single-Junction GaAs

The problem of expense factors in with the creation of the solar cell. GaAs cells are made by growing a series of very thin, single-crystal layers on top of a single-crystal substrate. Each layer is doped differently to form the positive-negative (p-n) junction by which solar electricity is made. The main expense lies in the production of that single-crystal substrate.

It is essential that the substrate and gallium-arsenide have a very similar crystalline structure. So naturally, gallium arsenide is the material of choice for creating the substrate. The problem is that GaAs is not cheap. Costs have been estimated at $10,000 per square meter, although Sandia National Laboratory refutes such claims as misleading.

Regardless, the cells are expensive. They are most competitive in concentrator photovoltaic systems, which use very small cells. Some potential solutions for dropping the price of these otherwise very worthwhile solar cells include creating reusable substrates or finding cheaper substrates. Closest to gallium arsenide in crystalline structure are silicon and germanium, both much cheaper.

Multi-Junction GaAs

Modern gallium arsenide solar cells are multi-junction cells. They hold the world record for conversion efficiency at 40.7% in a concentrator under lab conditions. Multi-junction, or tandem, solar cells are a combination of GaAs and other semiconductors, including germanium (Ge) and gallium-indium-phosphide (GaInP).

Tandem solar cells that use those three semiconductors are growing rapidly in popularity, spawned by the potential for a high efficiency solar cell. The GaAs/Ge/GaInP combination is so popular because together, the three semiconductors absorb a vast range of the solar spectrum. Companies and university researchers continue to focus on ways to reduce cell production costs.

In the meantime, GaAs solar cells continue to have an impact in outer space. For example, GaAs-based cells are currently being used on Mars Rover missions.

Monocrystalline Solar Cells / Amorphous Silicon Solar Cells / Gallium Arsenide Solar Cells / CIGS Solar Cells / Polycrystalline Solar Cells / Copper Indium Selenide Solar Cells