Excessive charge carrier densities in the emission layer of organic light-emitting diodes (OLEDs) can lead to significant
quenching by triplet-polaron-annihilation  or field-induced quenching . Thus, to increase the efficiency of OLEDs
further, a technique for the reliable determination of charge carrier densities in OLEDs is most desirable.
Time-resolved spectroscopy is a powerful tool to investigate electronic and excitonic transfer processes . By
application of a voltage pulse to a phosphorescent state-of-the-art OLED we find a transient overshoot after voltage turn-off.
This has primarily been found in phosphorescent OLEDs and has typically been attributed to delayed recombination
of trapped charge carriers [4-7].
In this contribution we investigate charge carrier accumulation within the emission layer (EML) and provide a method to
quantify the density of stored electrons.