19 Apr 2020

Solar Cell Technology Has Smashed Three Big Records

19 Apr 2020  by CARLY CASSELLA   
the world is grappling with more than just the climate crisis, and yet even now, in the face of a global pandemic, scientists are marching on with renewable solutions.

Just this month, no less than three records have been broken in solar panel efficiency. The first and the second were achieved by scientists in the United States at the National Renewable Energy Laboratory (NREL).

Their unique "six-junction" solar cell has unprecedented energy conversion, turning intensified light into electricity at 47.1 percent efficiency - the most efficient in the world under concentrated light conditions. This record beat the previous contender established just a couple of years ago by one percent.

"This device really demonstrates the extraordinary potential of multijunction solar cells," says John Geisz who works at NREL.

The achievement was helped by concentrating sunlight until it was a sizzling 143 times more intense. But even under the illumination of a single Sun, the solar cell is better than any other.

This is the second record broken - the team tested another version of their six-junction cell without concentrating the light, and achieved an unprecedented 39.2 percent efficiency.

Essentially this means that even more of the Sun's energy can now be converted into electricity.

Each of the cell's six junctions is specialised to capture a particular range of light from somewhere on the solar spectrum. Combined, the device contains 140 layers of light-absorbing material, and yet it is three times thinner than a hair off your head.

"One way to reduce cost is to reduce the required area," explains Ryan France, a materials scientist at NREL, "and you can do that by using a mirror to capture the light and focus the light down to a point."

By honing the light in this way, you not only spend a hundredth or even a thousandth of the material cost, the cell itself also becomes more efficient.

It's impossible to ever reach 100 percent efficiency because of the laws of thermodynamics, but reaching the halfway point would be quite the achievement, and France says that's "actually very achievable".

As we inch closer and closer to that goal, records like this one are constantly being broken across all types of solar cells.

The third record broken this month, for instance, was achieved by something called a tandem cell. This is a device, only a few micrometres thick, that combines two different semiconductors, one for the visible parts of the light spectrum and the other for infrared light.

Engineers from the German research centre Helmholtz-Zentrum Berlin created a new kind of tandem cell made from stacked silicon and perovskite with a certified efficiency of 24.16 percent.

"This combination is also extremely lightweight and stable against irradiation, and could be suitable for applications in satellite technology in space," says Steve Albrecht at Helmholtz-Zentrum Berlin.

The NREL has been charting the rise of efficiency levels in all types of solar cells since 1976. and compounds like the ones used in tandem cells have only been included in the past few years. Nevertheless, this light-absorbing material has increased in efficiency more than any other material since then.

It's only a matter of time before this tandem cell is succeeded by another, and for once at least, that's a global energy record we actually want to hit.

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