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Black Silicon-Powered Photovoltaic Device Offers 132% Efficiency

Don't worry, we're still complying with the laws of the universe.

Researchers at Aalto University in Finland have come up with a photovoltaic device design that has a quantum efficiency of 132%.

This impressive and seemingly improbable exploit was made possible thanks to nanostructured black silicon, a semiconductor material accidentally discovered in the 80s that has very low reflectivity and high light absorption. This achievement could prove to be a major leap in solar cell technology.

Hypothetically, if a device has a 100% quantum efficiency, every photon that hits the device will generate one electron, which will be carried through the circuitry to be generated into electricity.

This device, however, presents itself with a whopping 132% efficiency. What this means in actuality is that each photon will generate an electron with a roughly 1/3 chance that an additional electron will be knocked off its orbit and join the circuit.

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I can hear you all raising your voices "Bu... but what about the laws of physics? We can't just create electricity from nothing!"

To understand how this is possible, we first have to understand how photovoltaic materials work. When a photon hits the surface of a photovoltaic device, an electron gets knocked off its orbit. In certain circumstances, a high energy photon can bump two electrons off their orbit. So we're still complying with the laws of our universe here. 

In many solar cells, certain factors lead to a loss of efficiency. Sometimes photons get reflected off the surface of the device without interacting with its electrons or knocked off electrons fill the hole left on another atom before joining the circuitry.

So with their recent development, the Aalto team state that they have largely moved past these barriers. Black silicon absorbs photons far more efficiently than other materials and its nanostructure with cones and columns largely prevents the recombination of electrons on the surface.

The team states that this record-breaking efficiency could be used to improve any kind of photodetector, be it solar cells or light sensors for other purposes.

 The research has been accepted for publication on Physical Review Letters on July 28, 2020.

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