Staggering solar cell breakthrough converts light to electricity with 132 percent efficiency

WHY THIS MATTERS IN BRIEF

The world needs to decarbonise the atmosphere and dramatically reduce carbon emissions, and innovations are coming thick and fast.

 

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Today’s solar panels are a measly 17 percent efficient on average, but recently researchers in the US developed a world record breaking prototype that was almost 50 percent efficient, and we have a clear roadmap to achieving a staggering 80 percent, as well as creating spray on solar panels, as well as solar panels that generate electricity from rain and snow, as well as at night and in cloudy conditions.

 

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Now though even those achievements look measly in comparison to what researchers at Aalto University in Finland have achieved after they announced the development of a photovoltaic device that has an external quantum efficiency of an amazing 132 percent.

This impossible sounding feat was achieved using nanostructured black silicon, and needless to say could represent a major breakthrough for solar cells.

Walking you through this, if a hypothetical photovoltaic device has an external quantum efficiency of 100 percent then that means that every photon of light that strikes it generates one electron, which exits through the circuit and is harvested as electricity.

 

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This new device though is the first to not only reach 100 percent efficiency, but exceed it. At 132 percent, that means you get on average 1.32 electrons for every photon. It was made using black silicon as the active material, with nanostructures shaped like cones and columns, absorbing UV light.

Obviously, you can’t have 0.32 of an electron, but put another way you have a 32 percent chance of generating two electrons from a single photon. On the surface it might sound impossible – after all, physics dictates that energy can’t be created from nothing. So where are these extra electrons coming from?

It all comes down to how photovoltaic materials work in general. When a photon of incoming light strikes the active material – usually silicon – it knocks an electron out of one of its atoms. But under certain circumstances, one high-energy photon could bump two electrons out, without violating any laws of physics.

 

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It goes without saying that tapping into that phenomenon could be extremely helpful for dramatically improving the design of solar cells. In many photovoltaic materials efficiency is lost in several ways, including photons being reflected away from the device, or electrons recombining with the “hole” they left in the atom before they can be collected by the circuit.

But the Aalto team says it’s largely removed these barriers. Black silicon absorbs far more photons than other materials, and the cone and column nanostructures reduce electron recombination at the surface of the material.

Together, these advances made for a device with over 130 percent external quantum efficiency. The team even had these results independently verified by the German National Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB).

 

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The researchers say that this record efficiency could improve the performance of basically any photodetector, including solar cells and other light sensors, and that the new detectors are already being manufactured for commercial use.

The research has been accepted for publication in the journal Physical Review Letters.

Source: Aalto University

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