The counterintuitive concept actually increases voltage and efficiency, according to the team at University of California, Berkeley, who worked with Alta Devices to produce a prototype.
PV cells produce electricity when photons from the sun hit the semiconductor, knocking electrons loose to flow free.
But this can also generate new photons, in a process called luminescence. The idea behind the new design is that these extra photons — which do not come directly from the sun — should be allowed to escape from the cell as easily as possible.
This has the effect of increasing the voltage that the cell is able to produce, leading to a new prototype with an efficiency of 28.3 per cent, up from the previous record for single-junction cells of 26 per cent.
‘Fundamentally, it’s because there’s a thermodynamic link between absorption and emission,’ said Owen Miller of UC Berkley.