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.