Why do we need tandem solar cells?

[derlin]

I have a general question about tandem solar cells.

So tandem solar cells are solar cells with multiple p-n junctions in them.

However, why can't we have a single junction solar cell with multiple wavelength absorbers in them? That is to say, why do tandem solar cells need to be split into two separate subcells? To be clear, I'm talking about this from the viewpoint of organic solar cells. So I'm imagining a bulk heterojunction solar cell, where the absorbing section is a blend of two different wavelength absorbers.

I have a suspicion that it has to do with the relative LUMO energy levels between the high and low wavelength absorbers and the charge-transfer process that transfers an electron from the donor's LUMO to the acceptor's LUMO. But I can't quite reason it out to my satisfaction.

Any ideas?

 

[Greg Bernhardt]

I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?

 

[derlin]

Ah its ok. I was just curious, so I didn't need a super concrete answer. I think my suspicion was correct in that if you had multiple donors, you would need multiple acceptors with matched LUMO levels to undergo the charge transfer process so that you wouldn't lose all of the energy from your high-energy absorbing donor molecule.