I was doing a bit of thinking recently, when I stumbled on an interesting idea. In a simplified sense, solar cells function by absorbing light and converting it into electrical energy. Since visible light is just electromagnetic radiation, would it be possible to build a "solar" cell that absorbs different wavelengths of electromagnetic radiation?

This question actually has two parts: The first is whether such a construction is actually possible. The second is whether such a construction is actually useful. Most of the electromagnetic spectrum is absorbed by the atmosphere, so I get the feeling targeting any of these absorbed frequencies wouldn't be useful on Earth, because there wouldn't be much energy left to absorb. However, they might be useful outside of Earth's atmosphere.

Here's a diagram of which electromagnetic frequencies are absorbed by the atmosphere, for reference: http://upload.wikimedia.org/wikipedia/commons/3/34/Atmospheric_electromagnetic_opacity.svg

I did a bit of thinking/research about what these alternate "solar" cells might look like. I would imagine that infrared/ultraviolet solar cells would be fairly similar to normal solar cells, and sure enough, some Googling revealed infrared/ultraviolet solar cells are actually something that's being worked on right now.

Below infrared light are radio waves. A "radio" solar cell is a much more interesting idea. I know that "capturing" an electromagnetic wave has a lot to do with the wave's wavelength. But of course, we already have tools to capture radio waves: antennas. So is a "radio wave solar cell" just an antenna? Does this mean that the units of a normal solar cell are basically just tiny antennas for light? If so, it bodes poorly for the idea of x-ray or gamma-ray solar cells, due to the small wavelengths involved.

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    $\begingroup$ So a couple points are probably worth mentioning. First, while solar cells only use the visible portion, which is about 1/10th of the EM range depicted, that does not necessarily mean that you will gain 10 times as much power by making use of the unused parts of the spectrum, primarily because the majority of the energy emitted by the sun is concentrated in the visible region. So the only useful portion would be to find a way to use the infrared portion (the UV, X-ray, gamma ray portion has almost no energy). $\endgroup$ – DumpsterDoofus May 15 '14 at 23:41
  • $\begingroup$ Second, you bring up an interesting analogy: "Does this mean that the units of a normal solar cell are basically just tiny antennas for light?" The answer is yes, and in fact, the analogy can be extended to more than just solar cells. For example, the reason things such as carrots and tomatoes are colored orange and red is due to light being absorbed by tiny antennas which are embedded in the vegetable's flesh; these antennas are called molecules. In the case of a solar cell, it's more complicated (band gap of the material etc), but the idea is somewhat similar. $\endgroup$ – DumpsterDoofus May 15 '14 at 23:45
  • $\begingroup$ @DumpsterDoofus Yeah, I figured a large portion of the spectrum would suffer from that problem. (a lack of energy at that frequency.) The color comment is quite interesting! I had never thought of it that way, but that makes perfect sense. I knew that the color of an object had to do with the wavelengths the molecules of that object absorb, but I had never considered them to be "tiny antennas". Quite enlightening. $\endgroup$ – jpfx1342 May 15 '14 at 23:59
  • $\begingroup$ Yeah, it's fairly similar. In an antenna, radio waves force electrons to sort of slosh back and forth in the metal rod, and the resonance frequency of this sloshing is in roughly the same region as the radio waves. Similarly, in molecules, visible light causes electron density to slosh back and forth in the molecule, and the sloshing resonant frequency is usually in the visible range. $\endgroup$ – DumpsterDoofus May 16 '14 at 0:05
  • $\begingroup$ That said, radio antennas are not very energy efficient. At least, not in the way of power generation. I think I read somewhere when I used to work on solar cells that below NIR, the energy one would acquire is just too low to be of significant use. $\endgroup$ – Jim May 16 '14 at 13:52

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