The performance of colloidal QD solar cells or LEDs degrade with successive IV measurements. Specifically, the resistance of the device drops to few kOhms.
Do you monitor the temperature of the samples during IV measurements? In general, solar cells have negative power temperature coefficient and such a drop is expected.
Is this change permanent? Are you making the measurement in air? Are your CQDs known to be sensitive to atmospheric conditions? I am dealing with PbS CQDs solar cells, performances normally decrease a little during measurement, but recover after keeping the device at rest for a while. I am thinking of thermally or radiatively activated conformation of the organic ligand or reversible redox.
You can monitor the change in the optical response of your CQDs after measurements by comparing the absorption/photoluminescence spectra (before vs after I-V).
Good luck
I'm using QDs to fabricate QDLED.
It is permanent. The device does recover but not fully. There is degradation. i do measure in ambient air. I guess the QDs (CdSe/Zns) that i use is stable under ambient air. I will try to measure the PL before and after measurement and see.
Thank you
Hi Ramesh,
For the QDLED, I assume you use an Al electrode? From OLEDs and OPV it is known that both organic transport layers and the Al electrode are very O2/H2O sensitive (In particular under operation). If you watch it on a microscope this should show as "black spots".
For the QD solar cells (PbS ) I currently work on, I observe a significantly improved stability of the IV curve when measuring in vacuum.
Best of luck,
Deniz
@Deniz : Thanks for the response.
I do use Al electrode. But the charge transport layers are not organic, they are inorganic. Other problem I notices when I measure the IV was the temperature of the device, which was way higher than room temperature.
I believe Al is better than Ag as a contact for these devices. And when you mention vacuum, what is the pressure?
@Ramesh:
I also see the temperature increase (by ~5-10K) under forward bias, which I guess is not avoidable with 2V*1A/cm^2 = 20kW/m^2.
The vacuum we use is between 1e-4 to 1e-6mbar, depending on the experiment. 1e-4 is usually fine for our experiments.
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