For traditional solar cells, higher illumination intensity should result in slightly higher efficiency. The current increases proportional to illumination, if this were the only effect the efficiency would stay the same. However, the open circuit voltage also increases (with the natural logarithm of illumination), and consequently the fill factor increases a little bit, too. In summary the efficiency is higher. There are two things which can counteract: if there is significant series resistance the fill factor may decrease at higher illumination. Also, if the cell temperature rises the open circuit voltage goes down. I don't know whether there are additional effects in quantum dot cells.

does you change the operating voltage than 1 V

The efficiency and the photocurrent and voltage that you can extract from the solar cell are different things indeed. Efficiency is the measure of how many photons are converted into recoverable electrons by the combined effect of the cell voltage and the photocurrent and the resistances etc measured into the fill factor. The efficiency measure should not change that much with irradiance (irradiance meaning the amount of photons you send), except in the case of heating the cell too much. However, the photocurrent will change as much as less or more photons strike the cell and the voltage will change if the cell is heated for example.

There are lots of web tutorials that explain in detail what the I-V curve of a solar cell measures and how a solar cell works as well as the individual factors that influence FF, Voc, Isc and the whole efficiency.

For traditional solar cells, higher illumination intensity should result in slightly higher efficiency. The current increases proportional to illumination, if this were the only effect the efficiency would stay the same. However, the open circuit voltage also increases (with the natural logarithm of illumination), and consequently the fill factor increases a little bit, too. In summary the efficiency is higher. There are two things which can counteract: if there is significant series resistance the fill factor may decrease at higher illumination. Also, if the cell temperature rises the open circuit voltage goes down. I don't know whether there are additional effects in quantum dot cells.

yes. Efficiency of a solar cell depends on the intensity of light illumination.

If the minority carrier lifetime is injection-level dependent, the measured efficiency will be different at different illumination levels. Additionally the series resistance will have different influence on the cell performance with increasing current density within the cell. This will be significant in "large" solar cells as industrial standards made from silicon. So I think it depends on the kind of cells and the present recombination path. Sorry but I don't know much about your material system.

Comments already made give you a good idea of the possible effects of changes in the ilumination level on the efficiency of a solar cell. To give a more accurate answer, it is important to know all the electrical parameters of the solar cell against the ilumination level.

As other responses have said, the efficiency of a cell may increase or decrease with increasing irradiance.

However, you should also challenge the accuracy of your experiment. The reference device that is used to measure the irradiance of your light source is probably calibrated at 1 Sun only. The effects mentioned in other answers (especially the temperature coefficient) that affect your cell eficiency will also affect your reference device. Therefore it is hard to distinguish an increase in the efficiency of your specimen cell from a decrease in the quantum efficiency of the reference device. The difference between 11.3% and 11.6% is small compared to typical accuracy in measuring solar cell efficiency..

For all PV devices the efficiency goes up with increasing light level until series resistance losses forces it to go down. In the region where it is going up the current versus voltage characteristics are dominated by the diode properties. At very low light levels the dark current or the current from the parallel shunt resistance dominates the fill factor. The flat region in the efficiency versus concentration is where the fill factor is decreasing with increasing light because it is limited by series resistance and the voltage is still increasing logarithmically with light. For concentrator cells this peak is near the design point such as 500 suns concentration for 1-sun devices this point is near 1-sun. The only difference between 1-sun cells and concentrator cells for some technologies is the series resistance losses in the metallization.

As pointed out previously when you change the light level you must be careful not to change the spectrum or spatial nonuniformity or you will have an additional error as a function of light level. If the temperature is not well controlled changing the light level may also change temperature gradient between the temperature controlled plate and the cell junction.

We have done some testing, and published it here:

Paper

Thanks for your valuable answers.

The efficiency should not change much with the illumination. However there are several factor for slight change as stated earlier such as temperature, resistance, e.t.c

Only at very low illumination the efficiency is low but at higher illumination it saturates to a stable value unless there is a temperature rise. In concentrated silicon solar cells, up to 50 suns, the series resistance of the cell is reduced during fabrication to accomodate the high currents but the efficiency still remains same provided the tempterature is not allowed to increase.

The solar cells are thermodynamical engines connected to the sun on one side and to the room temperature on the other side. Of course this is not Carnot boundary conditions since the boundary condition to the sun is not an impose temperature but an imposed flux (photons from stephan law). The cold side is at room temeprature if correctly linked to, but if the temperature of your cell change, then does also the real efficiency. In other words, increasing the flux may lead to an increase of the temperature...which reduce the efficiency...which may give you a constant output power whatever is your flux.

I would say all comments provided above are succinct for understanding and correct..!! If you are interested in increasing illumination and yet maintain same temperature, i would recommend you to use LED based solar simulator or LED light source. LED solar simulators when compared to traditional ones do not generate much heat as a consequence your measurements would be more accurate ..!!!

In the real world, a decrease of DNI from 1 sun to 0.5 sun means substantial change in the direct spectrum, with a pronounced red shift. What you obtain with a simulator (fixed spectrum) may not reproduce actual conditions, so you need to be careful about your conclusions, depending on the spectral response of your cell.

Theoretically, the conversion efficiency should increase with the light intensities. However, due to series resistance or other chip properties, the efficiency could change not much and even drop while the illumination ratio rises.

Dear Ramesh,

I know that i came very late and you have been ended you project.

In my answer i will not repeat what has been said. But i would like the advise the researcher in a similar situation to build capabilities to analyse their results. The the solar conversion efficiency is defined by:

Eta= Voc Isc FILL FACTOR/ INSOLATION, input solar radiation in watt. You just want to see how the ISC, Voc and the fill factor vary with the input solar radiation. You must also be aware that the INSOLATION can heat uo the cell. Then it comes in play also the temperature T indirectly.

Since you measured the ETA, then you measured all its parameters. You need just to plot them versus the INSOLATION as you did for Eta. On this way you can can interpret your results.

So, you will find that Isc is proportional to the INSOLATION,

Voc= nVt ln Isc/Is where Is is the saturation current. Then the Voc changes logarithmic with Isc,

Since the range of the variation of your insulation is limited from one sun to 4 sun then Isc will increase by 4 times.

The ratio of the two inefficiencies eta at 4sun/ eta at one sun= ISC4 . VOC4 INSOLATION1/ Isc1 VOC1 INSOLATION4,

The FF and and T is considered more or less constant in this limited range of varaitions and that the used material are less sensitive to temperature variations.

Reducing the above equation one gets eta at 4sun/ eta at one sun= Voc4/VOC1= (Voc1+ delta Voc)/ Voc1 = 1+ dVoc/Voc1, dVoc/ Voc1= (nVt ln Isc4/Isc1)/ nVt ln ( Isc1/Is) which is a very small value.

Even you can calculate the this very slight increase in the Eta.

Best wishes