US Team Builds Solar Cell With 44.5 Percent Efficiency

Scientists at George Washington University and the US Naval Research Laboratory and the University of Illinois Urbana-Champaign have built a prototype for a new solar cell that is capable of capturing nearly all of the energy in the solar spectrum, resulting in 44.5 percent conversion efficiency.

The new device, which is based on GaSb, integrates multiple cells stacked into a single device and uses lenses to concentrate sunlight onto the tiny, micro-scale solar cells.

“Around 99 percent of the power contained in direct sunlight reaching the surface of Earth falls between wavelengths of 250 nm and 2500 nm, but conventional materials for high-efficiency multi-junction solar cells cannot capture this entire spectral range,” said Matthew Lumb, lead author of the study and a research scientist at the GW School of Engineering and Applied Science.

“Our new device is able to unlock the energy stored in the long-wavelength photons, which are lost in conventional solar cells, and therefore provides a pathway to realising the ultimate multi-junction solar cell.”
While scientists have worked towards more efficient solar cells for years, this approach has two novel aspects. First, it uses a family of materials based on GaSb substrates, which are usually found in applications for infra-red lasers and photodetectors. The novel GaSb-based solar cells are assembled into a stacked structure along with high efficiency solar cells grown on conventional substrates that capture shorter wavelength solar photons. In addition, the stacking procedure uses transfer-printing, which enables 3D assembly of the devices with a high degree of precision.
This particular solar cell is very expensive, however researchers believe it was important to show the upper limit of what is possible in terms of efficiency and they think the technique used to create the cells shows much promise. The research builds off of the advancements made by the MOSAIC Program, a $24 million research project funded by the Advanced Research Projects Agency-Energy (ARPA-E).’GaSb-based Solar Cells for Full Solar Spectrum Energy Harvesting’ was published in Advanced Energy Materials.