Greetings!
It is common to have efficiency roll-off in LEDs (be it quantum dot based, perovskite or OLEDs) at high injection current densities. Does anyone have an opinion on an opposite trend in LEDs at low injection currents?
I came across a surprising trend in my devices - perovskite LEDs where upon charge balancing via doping of transport/injection layers, we improve EQE roll-off at high current densities. However, the devices also show a very small turn on current and consequently, the EQE stay extremely flat over a wide current range. In both cases (in the attached Figure) the perovskite composition remain exactly the same and I do not expect such a trend.
Dear Azhar,
This is a good question. In order to explain the fall of external quantum efficiency at low diode currents you need to measure the I-V characteristics of the diode in the whole range of the operating current. If we could get out the current conduction mechanism in the diode we can explian the fall of EQE at low and high currents. Please also display the I-V curve of the diode.
Best wishes
Azhar,
The low current side typically caused by point defects through the so-called SRH recombination. Point defects can be saturated with increasing injection level, so the efficiency increases initially. The efficiency droop after the maximum point is more complicated.
See this paper for discussions: Article Interplay of point defects, extended defects, and carrier lo...
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