The Global View

Solar world record goes to NREL and back

Greenbang has just seen possibly the most efficient thing ever – not Mary Poppins tidying up the bedrooms of parentless kids using magic, but the US Department of Energy’s National Renewable Energy Laboratory or NREL, if you will, has busted the record for photovoltaic solar cell efficiency wide open, topping out at 40.8 per cent.

Greenbang didn’t realise that 41 per cent efficiency was such a cause for celebration. As soon as her boss disables Facebook at work, she aims to get her own efficiency rate up to the mid-30s. Maybe even higher once she’s had a cup of tea and a Hob Nob.

For the NREL though, the 41 per cent efficiency rate means how much of the light that falls on a cell can be converted into electricity.

The clever types over at the NREL reckon the cell they invented could be used in space satellites or terrestrial concentrated solar arrays.

More on how it all works from the horse’s mouth:

The new solar cell differs significantly from the previous record holder – also based on a NREL design. Instead of using a germanium wafer as the bottom junction of the device, the new design uses compositions of gallium indium phosphide and gallium indium arsenide to split the solar spectrum into three equal parts that are absorbed by each of the cell’s three junctions for higher potential efficiencies. This is accomplished by growing the solar cell on a gallium arsenide wafer, flipping it over, then removing the wafer. The resulting device is extremely thin and light and represents a new class of solar cells with advantages in performance, design, operation and cost.

NREL’s Mark Wanlass invented the original inverted cell, which recently won a R&D 100 award. His design was modified by a team led by John Geisz that further optimized the junction energies by making the middle junction metamorphic as well as the bottom junction. Metamorphic junctions are lattice mismatched – their atoms don’t line up. The material properties of the mismatched semiconductors allows for greater potential conversion of sunlight.