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Solar Cells That Emit Light Break Efficiency Record
benfrog writes "Researchers at the University of California-Berkeley say they have come up with a counter-intuitive way of making solar cells more efficient — making them emit light. In a press release the scientists claim to be the first to demonstrate that the better solar cells are at emitting photons (the more LED-like they are), the more efficient they are at generating electricity. However, 'unlike an LED, the electrons in a solar cell are absorbing photons from an exterior source as well as emitting their own.'"
If you've taken sophomore college physics, it's not counter-intuitive at all that an efficient absorber is also an efficient emitter.
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Ideally, you would want all of your electron-hole pairs to never recombine (which would keep them from emitting photons). Since that's obviously not possible, this would be the best possible outcome of internal recombination.
Because the light will be of lower energy (and therefore of a different wavelength) than that which the solar cells absorbed.
Basically, instead of heating up, these cells emit the energy in a controlled manner, in semi-directed infrared (probably) radiation. No laws of thermodynamics are being bent: The waste product is just closer to the type of the input than in other solar cells.
You could similarly say that a water turbine is more efficient if it lets water flow out: It is. The water will just have less flow strength than it did when it went in. The difference is what the turbine is collecting as energy. In this case, instead of letting the light 'back up' in the solar cells (as heat), it's released.
'Sensible' is a curse word.
Well, Physicists from MIT beat 100% efficiency a month ago. (of sorts).
The MIT team called it a LED that functions much like a heat pump. It emitted more optical power than the electrical power it consumed. Apparently the trick is that it results in a lower entropy state, and only works on extremely small scales, so it will never lead to a practical device.
This story, however, doesn't seem to say at all that they have broken 100% efficiency. They are trying to get the total efficiency up above 30%. The amount of light given out by the cell and the electrical energy given out add up to less than 100%. The slashdot headline leads you to believe that they broke 100%, but that is not what "efficiency record" means in this case.
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Just like how a speaker can be used as a microphone. It make noise when you run signal-carrying voltage through it, but also makes electricity when you scream into it.
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You still have to convert the energy from DC to AC so your DC appliances with AC2DC converters can plug into the wall. Damn you Tesla!
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Go read the article, maybe? The entire LED world is abuzz right now with that news. The only issue is that it requires a HOT ENVIRONMENT, where the LED seems to utilize by converting some of that energy into visible-wavelength emissions, beating the power input/optical power output ratio of 1:1.
Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
No, they fluoresce in near-UV (unless you're watching with an IR scope when using 680-700nm light.) Light conversion always works DOWN from higher energy potential to lower energy potential when there's no amplifier or booster present. We can take one blue photon and emit 7 or 8 red photons, roughly. This is why plants have this odd purple/red glow with certain near-uv wavelengths. They absorb blue, emit yellow/red photons as a result.
Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.