Photovoltaic cell - relationship between wavelength and intensity of Light

In summary, the conversation discusses the working principle of photovoltaic cells and the relationship between photon energy, intensity, and voltage/current output. It is mentioned that while the individual photon energy is important, the overall energy of a classical wave is determined by its intensity. It is also noted that photovoltaic cells have an optimal photon wavelength and can only absorb photons with energy equal to or greater than the band gap. More advanced materials can alter the band gap to capture more levels of photons.
  • #1
techguy
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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!
 
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  • #2
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
Thank you for your reply but i don;t really get your concept.

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
Do photons with an energy hf, less than the work function, convert their quantum energy primarily into thermal energy of the target?
 
  • #5
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.
 

1. How does the wavelength of light affect the efficiency of a photovoltaic cell?

The efficiency of a photovoltaic cell is directly related to the wavelength of light that it absorbs. Generally, shorter wavelengths, such as ultraviolet light, have higher energy and therefore are more efficient in generating electricity in a photovoltaic cell. However, most photovoltaic cells are designed to absorb a broader range of wavelengths, including visible and infrared light, to maximize their efficiency.

2. Can a photovoltaic cell produce electricity with low light intensity?

Yes, a photovoltaic cell can still produce electricity with low light intensity. However, the amount of electricity generated will be lower compared to when the cell is exposed to higher light intensity. This is because the number of photons (light particles) that reach the cell and are converted into electricity decreases with lower light intensity.

3. Is there a specific wavelength range that is most efficient for a photovoltaic cell?

Different types of photovoltaic cells have different optimal wavelength ranges. However, in general, the visible light spectrum (400-700 nanometers) is the most efficient range for most photovoltaic cells. This is because it is the range where the sun's radiation is strongest and most consistent.

4. How does the intensity of light affect the voltage output of a photovoltaic cell?

The intensity of light has a direct impact on the voltage output of a photovoltaic cell. As the intensity of light increases, the voltage output also increases. This is because more photons are being absorbed by the cell, producing a larger flow of electrons and therefore a higher voltage output. However, there is a limit to this relationship, as too much intensity can damage the cell.

5. Can a photovoltaic cell absorb all wavelengths of light?

No, a photovoltaic cell cannot absorb all wavelengths of light. Different types of cells are designed to absorb different ranges of wavelengths, and no single cell can absorb the entire spectrum of light. Additionally, some wavelengths, such as infrared and ultraviolet, are more difficult to capture and convert into electricity, so they may not be as efficient for a photovoltaic cell.

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