# Does Voltage of solar cell depends on Intensity of light?

On measuring voltage across the two terminal of solar panel (made of semiconductor material) ,the Voltage (V) increases with increase in intensity (I) of sunlight in open circuit. But it should be proportional to frequency, according to photo-electric effect. Why it seems like contrary?

(How PN junction solar cell differ from classical photoelectric cell)

This does not answer your question, but FYI, The situation may be a bit more complicated than you realize. A real, PN junction solar cell behaves somewhat like this circuit:

The value of the current source, $$I_{ph}$$, depends on the intensity of the light. The terminal voltage, $$V_{pv}$$, is related to $$I_{ph}$$ by the behavior of the other components, especially, by the PN junction itself which is represented by $$D$$. The $$R_{sh}$$ resistance cab be ignored if all you want is a first-order approximation.

The $$R_{s}$$ resistor only matters when the cell is connected to a load, in which case the behavior of the load plays as much of a role in determining the terminal voltage as the PV cell itself plays.

• (Looks)Its complicated. But where can I get source about this? Commented Aug 5 at 12:13

The classical photoelectric cell is not independent of the intensity of light. There is a minimum frequency required for the cell to generate a current, but if the incident light is above that frequency threshold, then the photoelectric cell output current is proportional to the intensity.

The Wikipedia article on the photoelectric effect says "An increase in the intensity of the same monochromatic light ..., which is proportional to the number of photons impinging on the surface in a given time, increases the rate at which electrons are ejected—the photoelectric current

Solar cells are essentially photoelectric cells. They are insensitive to incoming light below a certain frequency just like a photoelectric cell. See this webpage, for more information.

For both solar cells and photovoltaic cells if the incoming light is below a certain frequency, then it does not matter how intense the light is, it will not work.

In fact solar cells are mode out of photovoltaic cells. They are basically the same thing.

But in junction type, Voltage varies with Intensity. – Rajesh R

The important point is that power increases when the incident light intensity increases, whether it is due to an increase in current or an increase in voltage, since P=IV. I am finding it difficult to find a reference or a graph for a PN junction type solar cell that clearly demonstrates only the voltage increases with intensity. It might occur for the open circuit voltage where the electrons accumulate and have nowhere to go, but if a load resistance is present, the an increase in voltage would result in an increase in current since I=V/R. If R is constant, then V increases, then I must also increase. Can you find a reference for the relationship between output voltage of a PN junction type solar cell and intensity?

• if the incident light is above that frequency threshold, the output current (since P=VI) is increased. Right? Not the Voltage. But in solar cell, the voltage increase.. that's where it differ from classical P.E cell. That's why question arises Commented Aug 5 at 14:57
• My bad. I should of said the solar cell current increases instead of voltage. I have edited my answer to try and clear things up, but the essential point is that a solar cell IS a photovoltaic cell. with some voltage and current regulating components added on.
– KDP
Commented Aug 5 at 15:33
• Your definition is correct for Current (I) increase, with intensity particularly in normal cell. But in junction type, Voltage varies with Intensity. Commented Aug 5 at 15:39
• @RajeshR I have extended my answer in response to your comment.
– KDP
Commented Aug 5 at 16:22
• Thanks.. The increase in Power with intensity gives some clarity about it. I refer it from experiment (DIY). Give any reference if possible Commented Aug 5 at 16:40