While solar cell efficiency is theoretically able to reach 33.5 percent efficiency, so far solar cells have only been able to reach 26 percent until now. Eli Yablonovitch, principal researcher and UC Berkeley professor of electrical engineering has developed a new solar cell that will achieve 28.3 percent efficiency and it does so by emitting light.
“A great solar cell also needs to be a great Light Emitting Diode,” says Eli Yablonovitch, the Berkeley Lab electrical engineer who led this research. “This is counter-intuitive. Why should a solar cell be emitting photons? What we demonstrated is that the better a solar cell is at emitting photons, the higher its voltage and the greater the efficiency it can produce.”
Eli Yablonovitch and Owen Miller of UC Berkeley worked out the theory for the new solar cell efficiency. The monitor in the picture illustrates the new physics concept where increased light emission yields higher efficiency. (Image: Eli Yablonovitch)
“Fundamentally, it’s because there’s a thermodynamic link between absorption and emission,” said Owen Miller, a graduate student at UC Berkeley and a member of Yablonovitch’s group.
Designing solar cells to emit light, so that photons do not become “lost” within a cell, has the natural effect of increasing the voltage produced.
“If you have a solar cell that is a good emitter of light, it also makes it produce a higher voltage,” which would increase the amount of electrical energy that can be harvested from the cell for each unit of sunlight, Miller said.
co-founded by Yablonovitch, used the new concept to create a prototype
solar cell made of gallium arsenide (GaAs), a material often used to
make solar cells in satellites. The prototype broke the record, jumping
from 26% to 28.3% efficiency.
The company achieved this
milestone, in part, by designing the cell to allow light to escape as
easily as possible from the cell – using techniques that include, for
example, increasing the reflectivity of the rear mirror, which sends
incoming photons back out through the front of the device.