# Homework Help: What is the valance and conduction band?

1. Apr 20, 2013

### Levi Tate

Hello,

I am writing a technical essay on solar cells and I am having trouble finding out exactly what the valance and conduction band actually are. It's a bit elusive, the textbooks I am using simply state the two bands without explaining what they are.

If anybody could provide any references or explain this it would help me a great deal.

Thank you,
justin

2. Apr 20, 2013

### ShreyasR

Valence band and conduction bands are purely theoretical. It is how the working of semiconductors are explained. It is a part of "Energy band theory".
Instead of considering quantized energy levels(orbitals/shells), in this theory electrons of atoms in a crystal are distributed in terms of "energy bands". They say first band has n1 electrons, 2nd band has n2 electrons... and similarly the valence band and conduction band. "Valence band" can be considered as the all electrons of the valence shells of all the atoms in a crystal. Conduction band is the band of electrons which have acquired sufficient energy and left the atom (now free to move and can act as charge carriers)...

In text books, they simply state the two bands. I have given you a vague idea of what they are. If you want to understand better, you can search for "energy band theory" on google... But anyway, remember all these explanations are completely theoretical... You can predict what happens using a certain theory. If your prediction comes true, the theory is valid. If i say "According to energy band theory, for a photosensitive material, the energy gap between Valence band and conduction band is 'x' J/gram or whatever, if u supply that much amount of energy and the photosensitive material starts conducting, Then you can say that the theory explains it well!

3. Apr 21, 2013

### Levi Tate

Alright thank you. I realized that I do not have enough background in solid state physics to do this paper correctly, so I am basically just reading various sources and then regurgitating what I read, and referencing it. My teacher said this is fine though. He does research on semiconductors and superconductors in his lab so i will probably seem really dumb.