Black silicon photodetector breaks the 100% efficiency limit | Hacker News Reader

Black silicon photodetector breaks the 100% efficiency limit

phys.org

20 pointsMalic8 comments

When they say that the photodetector achieves 130% efficiency, red flags pop up for anyone trained in science. Is this device creating energy ex nihilo -- like a perpetual motion machine only more so?

It turns out what they mean is that each photon impinging on the device produces, on average, 1.3 electrons. So there is not an explicit claim from an energy perspective that the device is more than 100% efficient.

But it does raise the question: Could this technology be used to significantly boost the efficiency of solar cells? The article does not address that.

You're thinking about the energy conversion efficiency. They are claiming 130% quantum efficiency, i.e. the efficiency at which a photon can produce a free electron.

It is just another photomultiplier. These devices in various forms have been in existence since 1934.

I don't think multiple exciton generation (which is what you find searching for EQE > 100%) is exactly the same as the photoelectric effect. However, your point more or less stands.

It seems that these sort of devices are for sensors not generators. Higher QE leads to higher sensitivity according to the article. I would imagine that manufacturing costs would prevent any interest in making solar cells out of such devices.

> Aalto University researchers have developed a black silicon photodetector that has reached above 130% efficiency. Thus, for the first time, a photovoltaic device has exceeded the 100% limit, which has earlier been considered as the theoretical maximum for external quantum efficiency.

130% seems really interesting. Is it really just the color change?

> earlier been considered as the theoretical maximum

So... Was the theory (quantum electrodynamics) wrong?

No, the theory describes it (well mostly): https://en.wikipedia.org/wiki/Multiple_exciton_generation

Someone please inform me if I'm missing a subtlety, but this seems like news for this specific kind of photodetector not physics in general.

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