We are often asked why we use gallium arsenide (GaAs) to build our solar cells. It’s because GaAs naturally performs better at converting the sun’s energy into electricity than other materials under normal conditions. Further, GaAs solar cells deliver more energy in high heat or low light, two of the most common real-world conditions for solar cells! At Alta, we’ve developed a way to manufacture thin, flexible layers of GaAs that utilize only tiny amounts of material but retain all of the performance benefits of a traditional GaAs solar cell. This allows the solar cells to be cost-effectively incorporated into a wide variety of end products, bringing our vision of “Solar Everywhere” even closer to reality.
While the “layman” may not be familiar with GaAs, it’s been used to build solar cells for over four decades. That’s because the chemical and physical properties of GaAs make it the undisputed choice for high efficiency solar cells. For this reason, the space program has used GaAs solar cells for over 25 years, starting with the Mir space station and continuing to this day, with virtually every space bound vehicle incorporating GaAs solar cells. These types of cells are also used in terrestrial solar concentrating systems because of their ability to efficiently convert the sun’s energy into electricity.
At Alta, we use GaAs for our solar cells because this material has the ability to deliver the highest energy conversion efficiencies, which is a measure of how much of the sun’s energy is converted to electricity. In fact, all of the world records for high efficiency solar cells are held by some form of a GaAs solar cell. The unique properties of GaAs that lead to high efficiency include a direct band gap for efficient conversion of photons to electron-hole pairs. In turns out that the best GaAs solar cells operate very much like an LED, being almost equally capable of converting electricity to light as they are of converting light to electricity. As one of our founders is fond of saying, “The best solar cells also make great LEDs!”
The high efficiency of GaAs is not an artifact of the artificial conditions established under standard test conditions (STC). Under real world conditions, where changing levels of illumination and temperature are common, GaAs is a true standout compared to other materials. In fact, GaAs operates near its full efficiency at levels of illumination that are only one tenth of a sun, a level where most semiconductor materials have long since stopped operating as efficient solar cells. GaAs also has a temperature coefficient that is a mere one fifth of silicon and only one third of CIGS or CdTe. That means that at high temperature, GaAs continues to deliver energy at near its rated output, while the energy output of a silicon cell declines by 30% or more.
The only problem with GaAs is that the material itself is expensive. But another unique capability of the material comes to the rescue. It’s possible to grow extremely thin layers of GaAs that use just miniscule amounts of material, keeping the cost down. At the same time, these thin layers of semiconductor material actually get more efficient as they get thinner. The opposite is true for most other solar cell technologies. And a side benefit of these thin cells is that they are completely flexible and can be incorporated into any of today’s commercially available encapsulating materials. Even better, the flexible nature of these cells opens up the potential for a whole new generation of innovation in solar cell form factors that can dramatically reduce the cost of solar electricity.
We’ve recently released a pair of videos that describe the advantages of GaAs solar cells. Please watch them below: