# Photovoltaic cell - relationship between wavelength and intensity of Light

1. Oct 3, 2007

### techguy

Hi all, i am relative new here and i have an enquiry which i really wish to see if anyone can help me out with this.

From my understanding, photovoltaic cell works by using photons from light to generate eletricity. From what i know is that the lower the wavelength of light, the higher is the photon energy.

So does it mean that with intensity remaining constant, lower wavelength will generate a higher amount of voltage and current using the photovoltaic cell?

In other words, to have the same amount of voltage and current from the photovoltaic cell i can either use a high wavelength light with high intensity or a lower wavelength light with lower intensity. Am i right to say that?

Thank you so much peeps!

2. Oct 3, 2007

### cesiumfrog

No. If you were considering individual photons shone onto an ideal steam generator, sure the power output increases with the rate of photons and decreases with the wavelength of those photons.

But since you're not counting one photon at a time, then the photons composing your classical wave are irrelevent, and the energy of this is completely determined by the intensity. Perhaps it would help to think of colour (ie. the energy of the individual photon) as merely a measure of how many photons per unit of energy (rather than assuming that the photon rate would stay proportional to intensity, which was incorrect).

And for a typical photovoltaic cell I highly suspect that only a certain portion of energy can be taken from each photon, so for cell is only really efficient for a particular range of wavelengths.

3. Oct 8, 2007

### techguy

Lower wavelength i will get higher photon energy and the higher intensity i get more photons in the light right? if this is right, then doesn't that mean that high intensity with low wavelength of light will generate more voltage and current in the photovoltaic cell?

Thank you!

4. Oct 8, 2007

### Loren Booda

Do photons with an energy hf, less than the work function, convert their quantum energy primarily into thermal energy of the target?

5. Aug 26, 2010

### ACPower

Most photovoltaics have a single optimal photon wavelength whose energy corresponds to the 'band gap' of the material. The band gap is the voltage between the free electrons in the conduction layer and the bound electrons in the material. Photons with energy less than this band gap cannot be absorbed, photons with greater energy will presumably heat the cell, but will not change the output energy, which is due only to the fixed voltage of the band gap and the number of electrons knocked free. More advanced materials can alter the band gap with doping, or use multiple layers to capture more levels of photons.