Totally counter-intuitively, solar cells that emit light as well as absorbing it could actually mr much more efficient.
“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,” says Eli Yablonovitch, UC Berkeley professor of electrical engineering.
It’s long been known that there’s a limit to the amount of electrical energy that can be harvested from sunlight hitting a typical solar cell – theoretically, about 33.5 percent.
But current technologies struggle to get anywhere close – and, now, the scientists think they know why.
“Fundamentally, it’s because there’s a thermodynamic link between absorption and emission,” says graduate student Owen Miller.
Designing solar cells to emit light, so that photons don’t get ‘lost’ within a cell, automatically increases the voltage produced by the cell.
A solar cell that is a good emitter of light also produces a higher voltage, in turn increasing the amount of electrical energy that can be harvested from the cell for each unit of sunlight.
The theory that luminescent emission and voltage go hand in hand is not new. But the idea had never been considered for the design of solar cells before now, Miller continues.
A start-up co-founded by Yablonovitch, Alta Devices, has used the new concept to create a prototype solar cell made of gallium arsenide (GaAs) which has set a new record of 28.3 percent efficiency. He says he hopes to push this closer to 30 percent in the coming years.
