A better solar cell?

[[Tycho?]]

This is just something I thought up when reading about carbon nano-tubes.

 

It boils down to this: could carbon nano-tubes or other super tiny structures be used to create an "antenna" for light?

 

We use lengths of conductors to absorb radio waves, which generates a current in the conductor which is then amplified and converted to sound. Radio waves and microwaves can also be absorbed by a mesh of conducting material. The kicker for both these methods is that they must be around the size of the wavelength of the absorbed wave. I know for a faraday cage (the conducting mesh) the spaces in the mesh must be smaller than the wavelength they are going to absorb. I know an antenna has an optimal size for a given wavelenght, but I dont know what that is.

 

So, if one construced a conducting mesh with holes say 50 nm in diameter (or whatever), could a current be induced in the mesh if light struck it? If they could be absorbed like radio waves a solar cell made this way should be vastly more efficient than current solar cells. ...and like a million times more expensive.

 

Thoughts?

[mmalluck]

You'd have one of the same fundamental problems here as the do with solar cells: Light is made of several different wavelengths. It's for this reason solar cells will never have an efficency above 30% or so.

[mezarashi]

If you are referring to conventional solar cells, the main problem is not actually the current generated after the photon hits the atom, but rather, getting the photon to hit the atom in the first place !!!

 

Solar cells work by applying a reverse bias across a p-n junction to create a depletion region. Any photon that gets absorbed in the P and N region will indeed create an electron-hole pair, but will quickly be recombined thus not contributing to the current. The objective is to get the absorption to occur at the depletion zone where it will contribute to current. The problem is that this region is created BETWEEN the P and N layers... so how exactly do we get a reasonable amount of light to pass through and make contact? Much of the research in the field focuses on this concept... getting as high a ratio as possible of photons passing through the initial surface to create hopefully current contributing electron-hole carriers. This seeks to improve quantum efficiency.

 

You can probably see now why solar cells as we know them today are rather limited in their energy output. It's not only about getting photons to knock out electrons, but getting electrons to start "drifting" in a controlled and consequently meaningful way.