I noticed that there is a sudden rise in the current at certain voltage (please see attachment). Initially I thought it could be the problem of wire connection. However, it still presents after several runs. Also the similiar pattern presents in many of my samples. What could be the cause of it? I remember I have seen the discussion of it from a paper, mentioning it could be due to energy band mismatch, but I cannot recall where I see it. Anyone has any clue the potential cause of it?
Dear Chinjin,
One would like to see the dark i-v curve before commenting on the strange shape of the illuminated i-v curve. The second required data is the layer structure of the solar cell.It is required also to avoid any signal pick up apparatus. switched power supplies near the measuring setup can cause false indication in the display values.Also the scanning rate of i-v curve must be small enough to avoid any capacitive currents.
Dear Chenjin
I think energy band mismatch can be cause this problem, and why the dark current not found in the figure because shunt resistance relate for dark current for device (this mean structure of device).
With my best wishes
Hi Chenjin! I am very interested in this effect. One sometimes sees it when measuring the behaviour of things very different from solar cells. First however, make sure that other possibilities and issues as mentioned by Dr Taher and Prof Zekry have been fully addressed. Consider my suggestion ONLY if all other attempts to stop this behaviour fail.
This behaviour in semiconductor devices is usually caused by high frequency oscillation, far too fast for the measuring equipment to cope with. There are two quick ways to check this is. FIrst and easiest, just scan the cell but touch the electrodes, this will definitely affect the oscillation and may stop it altogether. Second, connect a really good oscilloscope (1 GHz bandwidth minimum) to the cell and scan it. Set the scope to AC, 10 mV/cm (or the most sensitive range if 10 isn't available) The trace should remain completely clean. Any 'fuzzy' appearance on the trace will indicate oscillation.
Now - if you find any oscillation, you have two more questions to ask. First, why is it there at all. Solar cells do not and should not have, negative AC output impedances. If the effect is just a nuisance, you can usually stop it by putting a capacitor across it. However, that might not work if the effect is caused by internal tunneling. What sort of cell is it?
Now this raises a very interesting issue. If your cells are oscillating, you have devices that can convert sunlight directly into AC, which is, shall we say, rather interesting and, as far as I know, TOTALLY NOVEL. It is definitely worth exploring and if found to be true, it may be possible to considerably enhance the effect so that the conversion efficiency is significant. I would be very interested to know what you find!
Good luck with your research!
Hi Chenjin,
is this the curve of one module or of an array of multiple modules? If it is multiple modules it could be caused by partial shading see http://www.solarchoice.net.au/blog/partial-shading-is-bad-for-solar-panels-power-systems/ for more information.
Best Regards,
Joshua Gray
Does this happen always at the same voltage or is it a random surge in current? Check the light source as well.
All the best
Paulson
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