A team at Australia’s UNSW, led by Dr. Mark Keevers and Professor Martin Green, have developed a solar cell design capable of converting unfocused solar energy into electricity at a ground-breaking 34.5% efficiency.
Dr. Mark Keevers and the prototype. Image courtesy of UNSW.
What’s truly exceptional about this level of efficiency is that it’s being achieved when converting unfocused light. This means that the cell can attain 34.5% efficiency when converting light that’s naturally occurring. In the past, efficiency levels have been measured when taking only focused light into account, light that had been concentrated with the use of mirrors.
This cell is markedly more efficient, even when left to absorb light from a rooftop with no light concentration.
The key to the cells’ hyper-efficiency is the use of prisms. By using a prism, the module is capable of trapping light and bouncing it around. This allows more opportunity for light energy to be absorbed before it can escape by reflecting away. It splits the incoming light into four bands that are then caught by a four-junction solar cell system.
On one side of the prism is a silicon cell. On the other side is a triple-junction cell. The triple-junction cell has three layers: germanium, indium-gallium-phosphide, and indium-gallium-arsenide. Each of these targets a specific wavelength of sunlight, essentially catching as much energy as possible via a multi-tiered filtering system. Much of the energy that the triple-junction cell does not catch, i.e. infrared light, ends up caught by the silicon cell.
Illustration of the four-junction system. Image courtesy of UNSW.
In addition to its extraordinary efficiency, the new solar cell design is also remarkably compact. The module in its entirety easily fits in the palm of one hand.
Photograph by Christopher Pearce. Image courtesy of the Sydney Morning Herald.
UNSW’s work with the Australian Centre for Advanced Photovoltaics (of which Professor Green is director and Dr. Keever is a Senior Fellow) has been producing large strides in solar technology for over 40 years. In 1989, it was UNSW researchers that first achieved 20% conversion efficiency with a photovoltaic cell.
In 2014, Keevers and his team at UNSW made news for breaking the world record for the highest solar energy conversion rate achieved for concentrated light— 40%. They accomplished this high efficiency by using commercially-available solar cells with a custom-made optical bandpass filter. The filter was able to capture and convert concentrated solar energy that was unavailable to the solar cells on their own, thus boosting overall efficiency to unprecedented levels.
The next step, according to Keevers, is to scale up the module so that it can be used outside of academia. Additionally, he says that the four-junction system could theoretically yield as much as 53% efficiency in the future.
Down the line, the team will aim to design a version of the module that’s capable of being manufactured for everyday use. Unfortunately, the new cell prototype is currently too expensive for mass commercial production. It could be several years before the modules become cheap enough to put on our roofs.