The Future of Green: Record-Breaking Solar Cells

**This is the fifth installment of our new blog series: The Future of Green. Every other Friday we will post a blog about a cutting-edge and futuristic innovation in the world of green technology. Technology is one of several barriers that stand between today’s society and a sustainable future. The innovators we highlight through The Future of Green are shattering those barriers. Make sure to tune in every other Friday for a glimpse into the future of energy and sustainability.

Solar technology has long been held back by low conversion efficiency levels. In other words, we can only convert a small amount of the sun’s potential energy into electricity. That’s all beginning to change, though, as conversion efficiency levels have soared in recent years.

A European research team recently set a new solar efficiency record—44.7%. The team—consisting of the Fraunhofer Institute, semiconductor manufacturer Soltec, R&D organization CEA-Leti, and the Helmholtz Center Berlin—utilized multi-junction solar cell technology, intended to capture the widest possible range of the solar spectrum.

The team had previously achieved 43.6% efficiency a few months ago. That record was then broken by Sharp’s 44.4% mark this summer. The current record of 44.7% will likely be surpassed before long.

The technology that allowed them to break the record is a bit complicated. Sunlight is made up of a range of energies from zero to four electron volts. Conventional solar cells have one photovoltaic junction, allowing them to only capture the energy of a small portion of the photon spectrum. The rest of the photons are essentially wasted.

To overcome this inefficiency, researchers have developed “multijunction” solar cells. These cells have multiple layers of materials, which creates multiple junctions that allow them to capture the energy from photons across the entire spectrum. The record-breaking solar cells have four junctions.

“This four-junction solar cell contains our collected expertise in this area over many years. Besides improved materials and optimization of the structure, a new procedure called wafer bonding plays a central role. With this technology, we are able to connect two semiconductor crystals, which otherwise cannot be grown on top of each other with high crystal quality,” said Fraunhofer ISE Department Head Frank Dimroth.

Technology that allowed for multi-junction cells was first developed in the 1980s. The first two-junction cell appeared in 1990, with the first three-junction cell following in 2001. For a more detailed (and scientific) account of this progress, check this out.

Solar cells that allow for close to 50% efficiency are not commercially available, and it will probably be a long time until they are. Most commercially-available PV solar panels have efficiency levels between 15% and 20%. To put that in perspective, wind energy is about 30% efficient, while hydropower is about 90% efficient. Nevertheless, increasing conversion efficiency levels for solar panels is a good sign. Eventually, this increased efficiency will translate into lower prices for consumers.

Keep an eye out for the next edition of The Future of Green, which will be published on October 11th. And revisit some of the previous installments: Automatic Light Switches Reimagined, Smart Windows, The Hyperloop, and Floating Offshore Wind Turbines.