While the spectrum-splitting high-efficiency four junction modules may be too expensive for homes, they could work with solar towers that concentrate sunlight, such as this one in Spain.

CULTURA RM EXCLUSIVE/RUSS ROHDE

Australian engineers have chalked up a world record for electricity conversion efficiency by solar cells of 34.5%.

The previous record, set by US company Alta Devices, was 24%. The result was verified by the US National Renewable Energy Laboratory.

Mark Keevers and Martin Green of the University of New South Wales in Sydney, used a 28 square centimetre module, embedded in a prism, to split incoming sunlight into four bands, and a hybrid four-junction receiver to maximise the amount of electricity generated from each beam.

The Alta record was achieved using an 800 square centimetre module.

This record is for unfocused sunlight. The same men already hold another record (at 40% efficiency) for focused sunlight, in a n experiment using mirrors to concentrate the light before splitting out various wavelengths.

“This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient,” said Keevers.

Mark Keevers with one of the spectrum splitting, four-junction mini-modules.

UNSW

Green said this level of efficiency had not been expected for many years.

“A recent study by Germany’s Agora Energiewende think tank set an aggressive target of 35% efficiency by 2050 for a module that uses unconcentrated sunlight, such as the standard ones on family homes,” he said.

The record-setting UNSW mini-module combines a silicon cell on one face of a glass prism, with a triple-junction solar cell on the other.

The triple-junction cell targets discrete bands of the incoming sunlight, using a combination of three layers – indium-gallium-phosphide, indium-gallium-arsenide, and germanium.

A diagram of the spectrum-splitting, four-junction mini-module.

UNSW

As sunlight passes through each layer, energy is extracted by each junction at its most efficient wavelength, while the unused part of the light passes through to the next layer, and so on.

However, Multi-junction solar cells of this type are unlikely to find their way onto the rooftops of homes and offices soon, UNSW cautioned in a press release, as they cost more to manufacture than standard crystalline silicon cells with a single junction.

Nevertheless, the spectrum-splitting approach is perfect for solar towers which use mirrors to concentrate sunlight which is then converted directly into electricity, the university said.