Energy

Black silicon photodetector hits record-breaking 132% efficiency

Black silicon photodetector hi...
An artist's illustration of UV light triggering electron multiplication in nanostructured black silicon
An artist's illustration of UV light triggering electron multiplication in nanostructured black silicon
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An artist's illustration of UV light triggering electron multiplication in nanostructured black silicon
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An artist's illustration of UV light triggering electron multiplication in nanostructured black silicon

Researchers at Aalto University have developed a photovoltaic device that has an external quantum efficiency of 132 percent. This impossible-sounding feat was achieved using nanostructured black silicon, and could represent a major breakthrough for solar cells and other photodetectors.

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

This new device 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.

It goes without saying that tapping into that phenomenon could be extremely helpful for 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 130-percent external quantum efficiency. The team even had these results independently verified by the German National Metrology Institute, Physikalisch-Technische Bundesanstalt (PTB).

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

26 comments
Grunchy
HOLY COW
MattII
Sounds impressive, but let's see if it can be scaled up first.
anthony88
It's the end of the coal as we know it, and I feel fine....
El Greco
Nice. They should probably stop calling it efficiency though. Conversion ratio or gain.
Worzel
This could be bad news, for a UK company recently set up, claiming a 'massive' 27% efficiency.
Bodger
"This could be bad news, for a UK company recently set up, claiming a 'massive' 27% efficiency."

Not necessarily. It all depends on the costs involved when you get to commercial-scale power production. The number to watch there is power per cost. A cheap product that is "good enough" in mass production is sometimes far better than a super-expensive product even if the latter is more efficient in theory.
Chris Coles
My own belief is that we do not "strip" electrons; instead, that the electron is a part of the electromagnetic force field structure of the proton, which is formed around a dipole which acts as a source of both a positive and a negative sink to which the Electromagnetic Force filed is attached. As such the structure has to conform to Maxwell's law, that all positive fields must seek the closest negative sink, or extend to infinity. Thus we have an positive field that forms what is a near infinite spring surrounding that attachment; which has to also conform to a simple fact, that all positive fields repulse each other, and as such where that positive field attaches to the negative pole of the dipole, it must form a minute tube of repulsion all the way from the exterior of the proton, down to the negative face of the dipole. That that tube of repulsion forms a classic capillary tube, which is in fact, the electron we observe seemingly orbiting the proton. Now as all such protons are in constant rotating motion, the distance between each proton's electron, and the adjacent proton's electron must constantly change, and again, must obey Maxwell's law, so as the external electromagnetic force field of each proton must extend beyond the orbit of each proton's electron; then as they rotate, the come under the influence of that capillary tube and connect by being drawn down into the capillary. But that must only be for as long as the distance between them allows such a contact, for as rotation continues, the attachment must conform to Maxwell and move to the closest negative; in that way we observe the constant flow of photon's, relative to temperature of the mass under observation. Now, we have to understand that as these attachments constantly change, they must pass each other, but must repulse. It is my belief that all such electrons are generated by the attachments sliding past each other; under normal electromagnetic interaction laws. That all observed electrons supposedly "stripped" are in fact generated by the interaction of the external positive fields of each proton sliding past each other. When you rub a piece of amber with a cloth of wool, you do not strip electrons; you generate new ones by the interaction of the external electromagnetic force fields of the protons passing each other. Oh! for the record; my theories have been completely dismissed as fake. Food for thought?
Worzel
Second thoughts; most likely to be used for space machinery first, as the budgets are bigger.
Home use? Probably not for a long time yet.
sidmehta
Agree with Nestor. Impressive, but efficiency is the wrong word. If you are over 100% efficient you have a perpetual free energy machine. Which is obviously impossible.

vince
132% would be a 5 fold increase from the typical 27% efficiency of solar panels today. If they really could do this it would be phenomenal and solar would be so much cheaper than natural gas that the entire oil industry would shut down in just a few years.