Even though sunlight is the most abundant source of energy bathing our planet, converting that light directly into electricity is no small feat.
Photovoltaics (PV) - the technology that absorbs photons, producing free electrons then captured to create an electric current - are a constant work in progress. Although the basic principles have been around for decades, engineers are continuously trying to improve the efficiency, or the amount of light converted.
Now researchers from the University of New South Wales (UNSW) have announced a new record in solar cell efficiency for unfocused sunlight - the kind of light beaming down on the solar cells on your rooftop.
This efficiency record is a milestone 34.5%, and it was achieved by Dr Mark Keevers and Professor Martin Green of UNSW’s Australian Centre for Advanced Photovoltaics. It’s a huge improvement on the previous record-holding unfocused PV cell efficiency of 24%, by Alta Devices in the US.
“This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient,” Keevers said in a statement. “Extracting more energy from every beam of sunlight is critical to reducing the cost of electricity generated by solar cells as it lowers the investment needed, and delivering payback faster.”
In 2014 the UNSW team already set a world record of 40% efficiency when using mirrors to concentrate light, but this new technology uses no concentrators.
Instead, it’s a mini-module embedded in a glass prism - on the one face you have a regular silicon cell, while the other side hosts a triple-junction solar cell which hosts three layers of a different chemical composition, able to extract energy at the most efficient wavelength for each (see diagram).
The theoretical efficiency limit for this device is thought to be 53%, according to UNSW researchers.
The current mini-module - which was tested by US National Renewable Energy Laboratory - is only 28 cm2, however the engineers are confident it will scale, although with some potential efficiency losses.
“There’ll be some marginal loss from interconnection in the scale-up, but we are so far ahead that it’s entirely feasible,” says Keevers.
It might be a while before such devices are found on the rooftops of regular homes, because they’re more complex and more expensive to produce, however it’s a milestone in the quest towards the most efficient solar PV cell possible, and Australia is currently way in the lead when it comes to development.
“We must maintain the pace of photovoltaic research in Australia to ensure that we not only build on such tremendous results, but continue to bring benefits back to Australia,” says Professor Greene.