Dear Rajiv Daxini ,

I wonder whether you repeated the measurements. If the repeated measurements also give this behavior, then it may be more difficult to explain.

EDIT: I have noticed now that I missed the part that you mentioned that "the curve persists". I am keeping my answer below anyway. I hope you can figure out the cause.

On the other hand, if this is a "single-shot" measurement of data, I have a guess about what might have caused this behavior: If the light intensity or the angle of the device changed significantly right before the kink, after that instant the curve will suddenly jump to another trajectory.

Mine is just a guess. If you repeat the measurements and see the same thing, you should check for a different cause.

Best regards...

Ali Zeki, Thank you very much for your response. Yes, as you noted afterwards, I did repeat the measurements. Therefore, the cause you have suggested in your original answer is unlikely. Your insight is helpful nonetheless, as this is useful for my overall understanding of the effects of different factors on IV curves more generally. Thanks again for your time.

Hello Rajiv,

also for the 2nd IV curve a small kink is present at the same voltage (ca. 0.42V).

Maybe this effect can be attributed to thermal run-away (PV efficiency is general quite temperature sensistive) or to additional resistance within the loop (check if you have direct access to the module most internal voltage level).

Best regards.

Dear Rajiv Daxini ,

I am glad for the comments you wrote. Actually I had decided to delete my comment in the first position, but then I thought it would be rude.

I need to add that, normally, I read the complete question + explanations before writing an answer, but apparently the images covered some parts of your explanations (which is due to Researchgate's brief presentation style for long question explanations) which I noticed right after my first answer.

Best regards...

Thomas Rotter Thank you for your suggestions. Yes that's right, the kink occurs at a similar voltage for all cells. Unfortunately we cannot access the cells of the module tested since those cells are sealed within a window (for BIPV research). However, the temperature might have something to do with it, as you have suggested. Following spectral characterisation of the light source, it was found that the lamp emits light shifted significantly towards longer wavelengths, i.e. there is a lot of infrared light and hence a lot of heating. Further tests showed that at lower irradiances, using the same lamp, the kink was less pronounced if not entirely non-existent.

I plan to test the cells using another light source indoors (once we have one) and the sun outdoors (once the weather improves) to see if the problem is a result of the present lamp's spectral characteristics.

Thanks again for your input.

I wonder would you observe hysteresis if changing the direction of IV scan. Then, it might be something similar to

Liu, Pengyun et al. “Fundamental Understanding of Photocurrent Hysteresis in Perovskite Solar Cells.” Advanced Energy Materials 9 (2019): 1803017-1-1803017-33.

I like Pavlov's suggestion

It should be very informative to see the results of changing the speed of the scan

Hello, Rajiv!

Have you already measured the dark I--V characteristic? If not, can you do it? If yes, what does it show?

Dear Rajiv Daxini ,

Such anomalous behavior of the solar cell attracts me very much. It is always really challenging to solve such strange behavior.

I think the most probable cause is the nonuniform distribution of your collected current among the collecting busbars. It seems me that the current distribution changes with operating point of the solar cell. The busbars do not seen uniform.

You can check this theory by reducing the illumination the kink will be smaller with smaller shortcircuit current.

Best wishes

Dear Prof. Zekry,

I'm glad to see that you are still involved.

It is getting more complicated now, with the computer between the experiment and the data It would be nice to see the details of the measurement.

Regards,

Alan

Good morning professor Alan L. Fahrenbruch

The seen behavior can be thought to be caused by changing the series resistance of t he solar cell during the scanning process. This may be due to the change of the current distribution in the solar cell during the course of measuring the I-V characteristics. When the researcher makes good connections to the solar cells, this odd behavior will disappear.

The use of the coracoidal may not be the best electrical accessing method for the solar cell because it is a high current device. The best way is to solder the wires and or to make firm pressure contact.

I wish success for all!

Thank you again for your encouraging comment

Abdelhalim,

What is a coracoidal?

Alan

see

Conference Paper Heterointerfaces in MJ SC: IV curves and their peculiarities

Dear Alan,

Hope your are well!

Thank you for the word crocodile connector. The word crocodile is misspelled. I corrected it the text. Crocodile is a type of pressure contact similar to crocodile mouth. If you look at the pictures brought by Rajiv Daxini you can see such crocodile connectors.

Best wishes

Dear Abdelhalim,

Thank you for clearing up that mystery.

By the way, here is a interesting comment by my favorite philosopher, Stephen Fry:

"...physics is the theology that makes machines work..."

Regards, Alan