I have fabricated a QLED device FTO/NiO/CdSeZnS QD/ZnO nanoparticle/Al. When biased the emission is bright the instance I turn on the supply and die out immediately. Attached is the video of it.
Thank you. If the device is short, wouldn't that be permanent? Also there is no sudden change in current when the emission reduces. It remains constant at ~100 mA.
ah, OK, so the video wasn't playback but the device switsches emits intermittently? If the current stays constant then you want to check whether you may get surface currents flow or whether you just get current sinks at internal defects as you need to check where the charges disappear.
Dr. Walther
Yes, when the supply is turned ON, the device emits for a second and reduces to zero. Is there a way to understand these effects using IV characteristics? This is the only device characteristic that I have.
Ramesh,
Is this effect repeatable? i mean if you wait for sufficient time and repeat the experiment again you observe the same previous behavior or is it one shot behavior?
What is the voltage on the device and its area?
please display the i-v curve during and after the emission.
I could no down load your attached file.
Best wishes
Abdelhalim,
Thank you for the response.
Yes it is repeatable. After three days I tried again today and got the same behaviour. The voltage is 10 V and the area is 0.09 cm2. The device emits momentarily when I turn ON the supply and reduces to zero. Again when I turn OFF and turn it ON, it emits for a fraction of a second.
Thanks
Ramesh
The power dissipated in a very small volume of the active device may be to large such that it causes self heating of the device. It may be worse than that. I expect that the current is not homogeneously distributed across the device area. What is the area of the quantum dots compared to the overall area? The power dissipated in the device= 40mAX10V= 0.4 w which can affect very high power density in the very thin material.
-It is required that one increases the voltage on the device slowly and observe its radiation activity. At which current density it begins to emit and at which current density it begins to cease emission and the radiation intensity variation with current
- One has to observe the radiation distribution of the surface area.
- Infrared cameras can be used to find the temperature distribution
The most probable cause may be the self heating the active areas in the device.
Best wishes
Quantum dots are all over the 1.5 cm2 sample. The active ares where the anode and cathode overlap is 0.09 cm2.
I tried to driving the device with a low frequency (10 Hz) square pulse and emission pulses as well. But when I increased the frequency, the emission pulse becomes narrower and eventually stops emitting or at least cannot be perceived with naked eye. When the frequency is decreased the emission pulse is longer and more perceivable.
Ok , one thing may be do not let the QLED to drop below the cutoff (say 5V) .
input with an varies 5-10 pp (like a dc offset @ 5V) you do get this by a clamping circuit (one capacitor ) let the frequency be as is...
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