I fabricated some solar cell devices and I discovered that about 30% of the devices gave strange J-V curves as attached here.
I think you have pinholes which partially short circuit your cells and cause low shunting resistance. the Isc and the the Voc for cell b and c are close to typical values. I think you have to make some post annealing step to stabilize you cells.
In addition you have to reduce the pinholes. Moreover you have to elaborate the processing of the solar cells.
Best wishes
It seems poor interface between electrode and photoactive layer.
This might be caused by the onset of degradation in the active layer of those devices. High relative humidity during the fabrication process might be a culprit.
it is good if you can describe your cell's architecture and some detail of your processing method. There are so many factors affecting the JV curve for example, pinholes, degradation, layer thicknesses, shunting, poor HTM (the list goes on) or even the electrical connection. But it looks to me as your cells have poor contacts (between photoactive layers and electrodes, poor connection might also contributed to this).
@ Mokhtar: actually, the architecture of the cells is planar n-i-p and I used one-step spin-coating method.
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