5 ms·

Carbon can be anything from an electrical insulator (diamond) to a pseudo-superconductor (nanotubes). So it's "just" a matter of getting the correct structure t

by ph0rque 14y ago

Carbon can be anything from an electrical insulator (diamond) to a pseudo-superconductor (nanotubes). So it's "just" a matter of getting the correct structure to tailor the bandgap to the light we want to absorb. Also, I can think of an excellent use of IR solar cells: turning heat into electricity. Wouldn't it be cool if you could always keep the heat in your house less than 75 degrees F, and produce electricity in the process, because your whole floor is a huge IR solar cell?

Retric 14y ago
What? If your room and floor are the same temperature you can't extract energy from that system.
- ph0rque 14y ago
  I mean your ground floor (or basement floor, if you have a basement).
- mercuryrising 14y ago
  You can capture photons from the black body spectrum. You can't extract much energy, but you could get some.
  - Retric 14y ago
    Sure you 'capture' a few, but if everything is the same temperature your losing just as photons back up. It's a lot like the tiny paddlewheel attached to a ratchet Richard Feynman analyzed, you end up with an even dice roll 4/5 times you win but that 1/5 makes up for all those gains. PS: Don't forget solar cells work because the sun is hot, and there is plenty of black body radiation to go around.
  - ars 14y ago
    No, not unless the device is colder than whatever is shining on it. To make electricity the captured photons have to fall to a lower state - but if the solar cell is the same temperature the photons can't do that.
mercuryrising 14y ago
I was pretty giddy and had a lot of mental momentum before. It's a little more complicated than just tailoring the band gaps. Ideally, we would be able to push the band gap anywhere we want, and we might be able to with specialized doping and electric fields, but at the moment we haven't been able to get outside of the IR spectrum (at least in Graphene, which I know a bit more about). There may be some fundamental material property limits that we are unable to get around (I don't think this is the case, but it could happen). Because Silicon is similar to carbon, Silicon can do many of the things Carbon can. We know Silicon extremely, extremely well. We have been working out the kinks in it for 30 years, Intel has put billions of dollars into researching the material. We know how it works. Other materials fall off very quickly in our level of knowledge, we are still at the point in some of them that we know they work, but we don't know why. Carbon is getting a lot of attention, maybe because it's the next best step, or maybe because understanding Carbon will let us continue to push Silicon forward until years in the future when we have a better understanding of the material when we can transition nicely. As for making heat -> You could, but the peak wavelength from the black body spectrum of the room would be about 10 microns. These solar cells are significantly shorter wavelength than that (they're absorbing ~1 micron radiation). Also, the longer the wavelength the less energy you get per photon, which wouldn't fare very well. For heat to electricity, you need a TEG (thermoelectric generators, peltiers, something that uses the Seebeck effect) or a sterling engine of some kind. These work off temperature differentials. Unfortunately, thermodynamics is not nice about recouping energy, and they need high temperature differentials to function efficiently. Even then, the efficiency maxes at about 30% (Carnot efficiency for heat engines).
juiceandjuice 14y ago
Near infrared is effectively just light, and there's not a whole lot of it. It's not infrared from heat, like you are assuming. Near IR is generally up to 1400nm wavelength, where the infrared from heat isn't really a factor til you hit 4000nm. The intensities of NIR are too low to be worthwhile. The scientists made something that could see your remote control's LED, not your body heat.

by ph0rque 14y ago

Retric 14y ago

What? If your room and floor are the same temperature you can't extract energy from that system.

ph0rque 14y ago
I mean your ground floor (or basement floor, if you have a basement).
mercuryrising 14y ago
You can capture photons from the black body spectrum. You can't extract much energy, but you could get some.
- Retric 14y ago
  Sure you 'capture' a few, but if everything is the same temperature your losing just as photons back up. It's a lot like the tiny paddlewheel attached to a ratchet Richard Feynman analyzed, you end up with an even dice roll 4/5 times you win but that 1/5 makes up for all those gains. PS: Don't forget solar cells work because the sun is hot, and there is plenty of black body radiation to go around.
- ars 14y ago
  No, not unless the device is colder than whatever is shining on it. To make electricity the captured photons have to fall to a lower state - but if the solar cell is the same temperature the photons can't do that.

mercuryrising 14y ago

I was pretty giddy and had a lot of mental momentum before. It's a little more complicated than just tailoring the band gaps. Ideally, we would be able to push the band gap anywhere we want, and we might be able to with specialized doping and electric fields, but at the moment we haven't been able to get outside of the IR spectrum (at least in Graphene, which I know a bit more about). There may be some fundamental material property limits that we are unable to get around (I don't think this is the case, but it could happen). Because Silicon is similar to carbon, Silicon can do many of the things Carbon can. We know Silicon extremely, extremely well. We have been working out the kinks in it for 30 years, Intel has put billions of dollars into researching the material. We know how it works. Other materials fall off very quickly in our level of knowledge, we are still at the point in some of them that we know they work, but we don't know why. Carbon is getting a lot of attention, maybe because it's the next best step, or maybe because understanding Carbon will let us continue to push Silicon forward until years in the future when we have a better understanding of the material when we can transition nicely. As for making heat -> You could, but the peak wavelength from the black body spectrum of the room would be about 10 microns. These solar cells are significantly shorter wavelength than that (they're absorbing ~1 micron radiation). Also, the longer the wavelength the less energy you get per photon, which wouldn't fare very well. For heat to electricity, you need a TEG (thermoelectric generators, peltiers, something that uses the Seebeck effect) or a sterling engine of some kind. These work off temperature differentials. Unfortunately, thermodynamics is not nice about recouping energy, and they need high temperature differentials to function efficiently. Even then, the efficiency maxes at about 30% (Carnot efficiency for heat engines).

juiceandjuice 14y ago

Near infrared is effectively just light, and there's not a whole lot of it. It's not infrared from heat, like you are assuming. Near IR is generally up to 1400nm wavelength, where the infrared from heat isn't really a factor til you hit 4000nm. The intensities of NIR are too low to be worthwhile. The scientists made something that could see your remote control's LED, not your body heat.